Model Engine Maker

Engines => Your Own Design => Topic started by: strictlybusiness1 on July 18, 2014, 12:12:05 PM

Title: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on July 18, 2014, 12:12:05 PM
These are some photos of my custom built .90 cu in engine that I used to set straight away records with. All parts in the engine are custom made including, machined from solid crankcase, hardened steel front end, ceramic hybrid bearings, chromed plated cylinder, machined piston, hardened steel roller rod with rollers & retainer, automatic fuel metering carburetor, machined tuned pipe, etc., etc., etc.

There is so much detailed information & photos, it is hard to decide where to start. Many carefully designed fixtures & tooling were built on manual machines to enable the building of these engines. I will answer any question asked about the technical information used to build & test these extremely reliable high performance two cycle engines.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: ths on July 18, 2014, 03:03:23 PM
Looking at this, the word 'golly' comes to mind, used as a metaphor of course. Nice gear, looks well made. How do you factor in the chroming of the cylinder when making the piston? I take it that it is lapped until the fit is to spec? Hugh.
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Niels Abildgaard on July 18, 2014, 03:59:03 PM
Hello Jim
More music please.
What kind of beer can I bring You?
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on July 18, 2014, 04:23:51 PM
No lapping compounds of any kind, including non-embedding types, should ever be used to fit a piston in ABC or AAC engines. Cylinders are machined with their taper amount & then chrome plated with approximately .0015" thick chrome/ side. The cylinders are then ID ground & each high silicon piston is machined to fit with a particular amount of crunch. The pistons also have a taper cut on their ID down from the top for a distance of .100".  If done correctly there will be a distinct wear band where the piston rubs against the bore. This wear band remains there throughout the life of the piston, liner combination & it indicates that this is the area where the sealing takes place. Pistons are machined from RSA-444 T6 (30% silicon aluminum) bar stock with crystalline coated diamond tooling. Cylinders are made from C360 free machining brass, C544 Phosphor Bronze & 4032 silicon aluminum.

The photos show a typical chroming fixture, the piston's wear band, the fixture used to machine & ID grind tapered cylinders.

Jim Allen


 
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: JMcRae on July 18, 2014, 04:52:31 PM
Beautful work! may I ask what the connecting rod is made of?
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on July 18, 2014, 05:28:33 PM
The connecting rods are made of AISI S-7 shock resisting tool steel. The "I" beam is .156" thick X .282" wide & in the valley of the "I" beam it is .032" thick. The rods are finish machined except for the upper & lower holes, hardened with a fixture in standard hardening oil, double tempered & then align ground with both holes square to each other in two axes within .0002" over a distance of 6.000". The ID grinding of both holes is done to size within + or - .0001". There is no bushing used in the upper end of the connecting rod. The finished piece has a tested Rockwell of 58, a 315,000 psi tensile, a 210,000 psi yield & a Charpy value over 224 ft lbs. The connecting rod has survived test runs at more than 32,000 RPM.

A key part of this assembly is the machined retainer made of C-350 Maraging steel, 350,000 psi tensile at 60 Rc hardness. The retainer is a unique design that has two rollers in each window. Look carefully at the photo of the back end of the engine & you can see the two roller, one of a kind, retainer.  Metallurgy is very important when building very high performance two cycle engines.

The photos show the heat treating fixtures which are wrapped in sealed stainless steel bags to prevent decarburizing of the steel, the grinding fixture used & some typical retainers.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Roger B on July 18, 2014, 05:31:50 PM
Gosh  :o  Interesting stuff  :ThumbsUp:  :ThumbsUp:
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: JMcRae on July 18, 2014, 06:19:11 PM
Thanks for the info Jim, I am planning to build a twin four stroke with the same type of rod with roller bearings in the big end like yours.
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on July 18, 2014, 07:08:02 PM
When you make the connecting rod's roller assembly, DO NOT use a large amount of radial play in the assembly. In my .90 engine there is .0002" to .0003" total radial play in the assembly. Large amounts of radial play will cause the rollers to skid more than they already do as the engine rotates & it will cause the rollers to skew, or turn side ways, in relation to the axis of the crank pin. The results are high friction & heat. Double staggered slots in the bottom end insures adequate lubrication. A single slot is used in the top end with no bushing. Eliminating the roller assembly or bushing in the upper end allows the connecting rod's center distance to be lengthened to the maximum. Two things happen when the connecting rod is made this way; the reciprocating weight is lowered & the angularity of the connecting rod is reduced to the minimum. Both things are very important for any high performance engine. The hardened S-7 material (Rc 58) of the connecting rod runs directly on the full hard M-2 steel (Rc 65) wrist pin without any problem because the rotational speed in the top end is very low.

Several different materials have been tested for the crank pin which is pressed into the S-7 crankshaft. The press fit amount is .0013"+. The hole for the crank pin is ground. Crank pins have been made of full hard M-2, M-50 & AISI 52100 steels. All work equally well. The crankshafts temper temperature (600* F) gives it a 285,00 psi tensile, a 220,000 psi yield at 55 Rc. Nothing will happen with the very heavy press fit, however it will require an alignment fixture & approximately 18,000 psi to get the pin in.

The fixture shown is sometimes used to grind crank pin holes with a Themac tool post grinder.

Jim Allen

Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Marinus on July 18, 2014, 07:20:28 PM
Wow!! This is amazing! Great work on those engines. I am quessing that these engines can be used in a world record speed boat?
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: JMcRae on July 18, 2014, 07:31:07 PM
How fast is the record you set Jim?
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on July 18, 2014, 08:19:41 PM
I held the straight away record in X hydro from 1990 to 1996. The first record speed was 82.72 MPH with my 14 lb rigger. I kept improving the engine & in 1996  the same boat recorded a record speed of 87.89 mph. At this time when the boat exited the surveyed speed trap, readings with a Stalker radar gun read 95 mph. This told me the boat was much to heavy for its purpose. A new boat has been constructed which will weigh approximately 8 lbs when finished & I will compete again in 2015. Present day straight away speeds for a nitro powered engine in this class are at 128.21 MPH in the NAMBA organization & 120.58 in the IMPBA organization.

I also have done a great deal of research work with gas engines & recently brought the Toroidal head design to the model boat world. I plan to continue doing the research & development of very high performance miniature two cycle engines until I'm dead!

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on July 18, 2014, 08:34:20 PM
These are photos of work benches in my shop. Engine crankcases made from solid bar both steel & aluminum, mount made for a geared twin setup, carburetors, form for a carbon fiber tuned pipe, various types of induction valves & much stuff. This is not a job for me, but the most brain stimulating, fascinating thing that is never ending. Mechanical engineering developments continue to make higher levels of performance possible.

Cut & try!

Jim Allen

Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: JMcRae on July 18, 2014, 08:47:27 PM
Wow Jim that is a serious set of engines, I have a hydro that I run once and a while, nothing serious but by far the most fun to run out of all my r/c vehicles. May I ask where you are from?
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: rockknocker on July 18, 2014, 08:59:26 PM
Your research and development work is extremely impressive! I'm definitely looking forward to seeing everything that you share with us!

Your engine test stand looks like a useful fixture. Do you use it to run engines in or to get power measurements? Is propeller speed your primary method of determining an engine's performance or do you have a different method?

Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Ramon on July 18, 2014, 10:11:31 PM
Awesome - simply awesome - that truly is some extremely impressive work there Jim  :praise2: - not only in those superb parts and the finished engines but in the fixturing too - beautiful workmanship from an enviable knowledge base indeed.

I'm quite (but only just a little you understand ;)) envious of your heat treatment and cylindrical grinding facilities too - oh I wish ::)

Hoping to hear more about these fabulous creations

Regards - Ramon




Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on July 18, 2014, 11:37:39 PM
Wow Jim that is a serious set of engines, I have a hydro that I run once and a while, nothing serious but by far the most fun to run out of all my r/c vehicles. May I ask where you are from?

Lexington. North Carolina
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on July 19, 2014, 12:13:57 AM
Your research and development work is extremely impressive! I'm definitely looking forward to seeing everything that you share with us!

Your engine test stand looks like a useful fixture. Do you use it to run engines in or to get power measurements? Is propeller speed your primary method of determining an engine's performance or do you have a different method?

The engine test stand in my avatar is a custom made hydraulic dynamometer. It has an infinitely variable load capability, an electric tachometer that reads 0 to 50,000 RPM (every rotation) & a calibrated load cell with a digital readout to read the torque. I built this dyno in 1978 & rebuilt it in 2000. I use this to determine the brake HP of my engines. I also built two other HP measuring devices, one that would be described as a torque cradle which uses Dynamax fans as the load & another that uses various carbon fiber airplane propellers as the load.

The building of any engine would be very difficult, maybe impossible, without these instruments.  The photos show some of the key parts of the hydraulic dynamometer. It can absorb a maximum of 8 HP at RPM's exceeding 32,000. 1 HP is approximately 740 watts of heat. At 7 HP the rotor in the dynamometer housing absorbs 5200 watts of heat. The cold water comming in is heated instantly to 200 * F before it comes out. Dynamometer pulls usually last for 4 minutes at WOT.

Th hydraulic dynamometer shown has every piece doweled pinned in place. It can be disassembled & reassembled precisely without any type of alignment fixtures or jigs.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on July 19, 2014, 12:16:59 AM
The first three photos are of the hydraulic dynamometer rotor housing. The piece is precisely machined & does not require any type of sealing. The adjustable valve at the bottom changes the amount of load.The remaining photos are of the torque craddle. It's RPM limit is 30,000 because of the Dynamax fan units used as a loading device. Different size rings mounted to the front of the 3/8 thick  protection shroud vary the load.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: dieselpilot on July 19, 2014, 02:30:09 AM
1 HP is approximately 4700 watts of heat.

1HP is 746W. Still, 7HP (5.2kW) is roughly 20% more heat than a typical gas stove top burner on max heat. Have you run any of the Nelson engines on the dyno?

Jim, great stuff as usual. I've been reading about your work since 2008 or before.

Greg
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Niels Abildgaard on July 19, 2014, 05:30:18 AM
Please let us see a picture of crankshaft ,bearing and Coupling.What is mass of piston plus pin?.
The reason that You do not need needles in the upper conrod eye is that at 30000plus rpm piston is lifting against combustion pressure so that oil can come under pin.
For normal speed two stroke this is not the case .
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on July 19, 2014, 08:43:21 AM
1 HP is approximately 4700 watts of heat.

1HP is 746W. Still, 7HP (5.2kW) is roughly 20% more heat than a typical gas stove top burner on max heat. Have you run any of the Nelson engines on the dyno?

Jim, great stuff as usual. I've been reading about your work since 2008 or before.

Greg

Thanks for correcting the misprint Greg. 740 watts is plenty & 4700 would not be possible.

JA
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on July 19, 2014, 10:23:02 AM
Please let us see a picture of crankshaft ,bearing and Coupling.What is mass of piston plus pin?.
The reason that You do not need needles in the upper conrod eye is that at 30000plus rpm piston is lifting against combustion pressure so that oil can come under pin.
For normal speed two stroke this is not the case .

I had to search through my notes to find the mass numbers for entire rod assembly;
two rollers/ window retainer- .8 gms
16/ 0.627" OD rollers- 1.4 gms
steel "I" beam connecting rod- 12.5 gms
wrist pin (solid in the middle) .250" OD- 5 gms
piston- 15.6 gms

I believe that totals 35.3 gms & I use 33% of that total for the crankshaft counterbalance. The crankshaft weigh 132.4 gms.

I do not know if your thoughts about why no needles, rollers or bushing are not required on the top end is correct. The upper end assembly has .0001" total radial clearance & the bottom end has .0002" total radial clearance. The engine runs with .001" deck clearance without the piston hitting & the upper end of the rod is slotted for lubrication. I believe the metallurgy used prevents any galling or wear of the upper end parts. Notice that the upper end of the connecting rod is guided between the piston bosses without the use of any type of hardened thrust washers. The total axial clearance is .005". As to possibility of this working in a 125 or 250 cc two stroke racing engine, that question is unanswered.

I use the same type of connecting rod setup in my 22,000+ RPM, 26 cc gas engines. There have been no problems thus far. I believe that the squareness & rigidity of the engine's crankcase plays a major role in what is happening after the engine comes to temperature.

The next to last photo shows the entire roller assembly in place as it is used. Look carefully & the two rollers in each window of the retainer can be seen. The partial print shows the numbers involved with the bottom end roller assembly used in the 26 cc gas engines. The machining of the retainer proved to be essential in the building a very high RPM roller assembly. Since the rollers are guided along their center lines, from end to end, there is no skewing possible. The friction & heat that some thought would develop from two rollers touching dose not occur. The retainers are always guided in ID of whatever bore is used, with .001" total radial clearance. Notice that the retainers width at the center line of the rollers is .025" wide. The very low mass of the retainer & the tight radial clearance helps to decrease roller skidding to a minimum.

The second photo from the top shows how the crankshaft is mechanically fastened to the inner races of both front bearings by placing a hardened steel sleeve over the crankshaft between the two inner races. Since all the parts are made of steel, including the full hard AISI O-1, ground ID & OD front end, the axial play can be set when the engine is cold. It remains the same amount when the engine comes to temperature. The third photo shows the steel shim washers used with the hardened steel sleeve to set the crankshafts axial play at .004".

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on July 19, 2014, 10:48:39 AM
1 HP is approximately 4700 watts of heat.

1HP is 746W. Still, 7HP (5.2kW) is roughly 20% more heat than a typical gas stove top burner on max heat. Have you run any of the Nelson engines on the dyno?

Jim, great stuff as usual. I've been reading about your work since 2008 or before.

Greg

We have run many of the Q-40 & FAi engines with our standard test props. Dyno tests show that the FAI engine can produce approximately 4.5+ HP at 30,000 RPM on 15% fuel. We have used a data logger to determine the RPM's of the Q-40 engine in the air on a three pylon course. The engine reaches approximately 29,000 on the straights & loses approximately 500 RPM when turned. Speeds on the straight measured with a Stalker gun are approximately 200+ MPH. We have been able to raise the quality & consistency from engine to engine with our very detailed engine building program. At Aero Precision Machine, high precision machines such as Makino, Mori Seki & Bridgeport are available to produce very high precision parts. Each & every engine is assembled by the numbers, by me.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Admiral_dk on July 19, 2014, 12:56:50 PM
Whoa - you are working with stuff I used to dream of as a kid and young man and I'm impressed with the numbers too. They stopped racing 125 cc road racing motorcycles a few years back and they had reached some 430 HP/litre and you where at 482 HP/litre years ago  :NotWorthy:

I got plenty of questions, but right now I just want to ask three :

Your engines are the first where I can see very little clearance between the inside of the piston and the top end of the rod - why - is it to avoid problems at the bottom end of the rod ?

How do you ensure that you only plate the inside of the cylinder when all of it is in the electrolyte or have I misunderstood your pictures ?

I'm really interested in the plating process - it can be used on many other cylinders than those intended for the power part of a two stroke - is this a "standard chroming process" or is it hard chrome and what is the difference - electrolyte etc. in case it's not (the short version) ?

Thank you very much for sharing  :praise2:  :pinkelephant:  :praise2:
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on July 19, 2014, 03:28:11 PM
"Your engines are the first where I can see very little clearance between the inside of the piston and the top end of the rod - why - is it to avoid problems at the bottom end of the rod ?"

Yes. Notice that the upper end of my connecting rod is wider than the bottom end. In fact it is .375" wide in the top compared to .3125" wide in the bottom. Guiding the connecting rod in the bottom end can lead to frictional heat problems because the rotational speed in the bottom is high. Upper end guidance allows the bottom end to have a liberal amount of axial clearance (in my engines .015") , but keeps the connecting rod centered. There is no tilting of the cylinders axis to keep the connecting rod from moving off the cantilevered crankshaft when it is bending under load. Also the crankshaft of my engine has a  large diameter for an engine this size, .5906"  (15 mm). This helps to reduce the bending. Consider the crankshaft size used in all manufactured 23 to 30 cc engine is .4724" (12 mm). Even though these crankshafts are the three piece split type, with bearings on both side,  the bending still takes place. This would be true even in engines with four bearings, two on each side.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on July 19, 2014, 03:42:22 PM
"How do you ensure that you only plate the inside of the cylinder when all of it is in the electrolyte or have I misunderstood your pictures ?"

More photos should answer this question. The cylinder sits inside a brass sleeve which sits inside a PVC fixture. The PVC fixture enables the cathode connection to the cylinder & locates accurately the lead antimony anode in the center. The sleeve the cylinder sits in has purposely been made longer at the top & bottom of the sleeve to prevent a buildup of chrome at the top & bottom edge of the cylinder.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: dieselpilot on July 19, 2014, 03:52:18 PM
Thanks for that. I was curious how much power Q40 engines were making. I saw mention of 4+HP and didn't realize they were making that much these days.

Greg
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on July 19, 2014, 04:07:00 PM
"I'm really interested in the plating process - it can be used on many other cylinders than those intended for the power part of a two stroke - is this a "standard chroming process" or is it hard chrome and what is the difference - electrolyte etc. in case it's not (the short version) ?"

There are two basic types of chrome platting, decorative chrome plating (shiny stuff) & hard industrial chrome (not shinny). I use the standard Chromic Acid/Sulfate Bath mixed at a ratio of 100 to I. For example 33.3 ozs of CrO3 & 0.33 ozs of H2SO4 are mixed  in 1 gal of distilled H2O.  The bath is run at a current density of 3 amps/ sq in, including the brass fixture,  at 125* F. For a .90 size cylinder & fixture it takes 21 amps at 4.6 volts to plate .001" of chrome/ hour on the cylinder's ID. The bath's temperature & the current density will determine how hard the chrome plating will be. If done correctly the hard industrial chrome plating applied will exceed 1100 vickers. Carbide tools will have not effect on scratching this.

I also chrome plate 4032 aluminum cylinders, but the cleaning & etching process is much more involved. The cleaning of brass pieces is done with a strong alkaline solution. Steel pieces are reversed etched before the chroming process is started.

Jim allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on July 19, 2014, 04:18:36 PM
Thanks for that. I was curious how much power Q40 engines were making. I saw mention of 4+HP and didn't realize they were making that much these days.

Greg

We began to do some testing with the torque craddle at RPM's beyond 32,000. In fact the loading device we attempted to use was made of aluminum & was designed to withstand 40,000+ RPM. However, the device's mass prevented it from working at the higher RPM's. Sometimes careful calculations & design do not work out when cut & try time comes. The loading device certainly looked good on paper.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Stuart on July 19, 2014, 04:33:00 PM
Well I am in awe of the quality of your work ,which is of course backed up with a great depth of technical knowledge

Sir I take my hat off to you

I thought we were doing ok when we sorted out the veco 19 for car racing but after reading your thread we were only scratching the surface but we had to go to 95% nitro

Now I know we were only on the title page not Evan the first paragraph

Stuart

Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: JMcRae on July 19, 2014, 06:38:48 PM
Jim if I read this correctly you said you ran your engine on the dyno for 4 min at 30000rpm. That in its self is impressive. I have no doubt you will be on top of the competition in 2015.
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Niels Abildgaard on July 19, 2014, 08:20:51 PM
Please let us see a picture of crankshaft ,bearing and Coupling.What is mass of piston plus pin?.
The reason that You do not need needles in the upper conrod eye is that at 30000plus rpm piston is lifting against combustion pressure so that oil can come under pin.
For normal speed two stroke this is not the case .

wrist pin (solid in the middle) .250" OD- 5 gms
piston- 15.6 gms
Jim Allen

Let me explain.
If someone is familiar with locomotive engines then we can surely have a picture of a GM645(two stroke) piston/wristpin/conrod top end and a picture of the very much simpler fourstroke arrangment from GE.
In a four stroke engine piston will pull conrod longer when going through top dead center after exhaust before intake.This is Very nice because some oil go into the clearance between underside of wrist pin/conrod and is ready to lubricate next time we go top dead center where real serious pressure in cylinder certainely pushes piston downward.
Normal two strokes do not have this lifting of pin in eye at half the top center pasages and lubrication is really a pest.
It was therefore a  gift from heaven to two stroke designers when SKF started to design needle bearings for this purpose.
When east german motorbikes were equiped with needle bearing in upper conrod eye oil could be reduced from 6% to 3 or even lower.Talk of a measurable improvement of air quality.
What Jim is doing is running his engines so fast that piston actually pull or elongate conrod in top dead center and thus get a little oil dow this sore spot.
A little calculation in sensible units indicates that pressure in cylinder at top dead center shall be MORE than 50 bar to avoid this lifting and it is not 50 bar.No way.aint no turboed diesel.
If same engine was run at say 15000 rpm and had a pipe that really pushed mixture in it would destroy itself no time.
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Admiral_dk on July 19, 2014, 08:26:06 PM
Hi Jim

Thank you very much for your explanations - they do clarify some of my questions  :)  :praise2:

So if I see correctly - the way you put the cylinder inside the brass + PVC combo, prevents the electrolyte from coming in contact with anything you do not want plated - kind of what I expected, but didn't see on the first pictures, the additional helped quite a bit.

So you're telling me that the major difference between "normal" chrome and "hard chrome" is down to temperature and current density in surface of the object - nice to know, again thank you.

I can't help another question about this subject - is it always necessary to grind the cylinder afterwards or is that purely down to the extreme small tolerances you need in this engine size ?

Again thank you very much for enlightening us - it's really appreciated  :pinkelephant:

Best wishes

Per
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on July 19, 2014, 09:08:04 PM
Jim if I read this correctly you said you ran your engine on the dyno for 4 min at 30000rpm. That in its self is impressive. I have no doubt you will be on top of the competition in 2015.

The first hydraulic dyno was used primarily to develop a connecting rod that could survive at 30,000+ RPM. Many different alloys, high strength aluminums (7075, 7079, etc.), 6AL4V titanium, heat treatable high strength Beryllium copper alloys (C172, C173),  as well as many different types of roller assemblies all failed. The first clue came in the form of a machined O-1 steel rod that was not hardened. The rod had a hard steel race pressed in the bottom with two oil holes, a b-2 brass bushing pressed in the upper end & a hardened Beryllium copper retainer with 10 individual rollers. This rod survived 6 dyno pulls at more than 32,000 RPM. The only damage was the rotation of the bottom end hardened race which cut off the oil supply & blued the rollers. Selection of a shock resisting steel & making the connecting rod was the easy part. I removed the bushing in the upper end & no roller assembly was ever considered because I wanted two things that are necessary in high RPM engines. A rod to stroke ratio as close as possible of 2 to 1; the engines stroke is .902" & the center distance of the connecting rod's holes is 1.741". Close enough I think. I also wanted the reciprocating weight (upper half of the rod, the piston, wrist pin & circle clips) to be as low as possible. The wrist pin which is solid only in the middle is drilled from both ends.

Theories are always good, but cut & try always gives the answer. The very high cost in time & money can be seen in the posted photos!

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on July 19, 2014, 09:54:05 PM
Hi Jim

Thank you very much for your explanations - they do clarify some of my questions  :)  :praise2:

So if I see correctly - the way you put the cylinder inside the brass + PVC combo, prevents the electrolyte from coming in contact with anything you do not want plated - kind of what I expected, but didn't see on the first pictures, the additional helped quite a bit.

So you're telling me that the major difference between "normal" chrome and "hard chrome" is down to temperature and current density in surface of the object - nice to know, again thank you.

I can't help another question about this subject - is it always necessary to grind the cylinder afterwards or is that purely down to the extreme small tolerances you need in this engine size ?

Again thank you very much for enlightening us - it's really appreciated  :pinkelephant:

Best wishes

Per

Any cylinder that is hard chromed plated will need to be ground or honed.  Maybe I should explain further. Cylinders in nitro engines such as the Nelson are honed on a Sunnen honing machine to give a fine finish in a short amount of time. Cylinders in my .90 cu in engine are ground & will have an even better finish than honing. Cylinders for ringed gas engines are honed with a pattern which will help to seat the piston ring. However, there is on exception. Sometimes a hard chrome plating is applied to the crank pin of an engine that has a bushed rod in the bottom end. This will always be a smaller size engine & the bushing material (#510 phosphor bronze) will finish the chrome plating from normal running.

Jim Allen

JA
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on July 19, 2014, 10:21:51 PM
To clear up any misunderstanding about this engine, it is a tuned pipe engine. The tuned pipes are developed on the dyno & are machined from steel bar stock. The pipes used will increase the engines HP by approximately 45 to 50 %. This is another very interesting subject for another time.

The photos show the typical construction of a tuned pipe made from basic formulas & computer analysis. Again, nothing is proven to be true until that cut & try moment. Many tuned pipes end up in the garbage can.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on July 20, 2014, 12:19:27 PM
Well I am in awe of the quality of your work ,which is of course backed up with a great depth of technical knowledge

Sir I take my hat off to you

I thought we were doing ok when we sorted out the veco 19 for car racing but after reading your thread we were only scratching the surface but we had to go to 95% nitro

Now I know we were only on the title page not Evan the first paragraph

Stuart

Many fuels were tested on the dyno. One formula in particular gave the most HP & was not greatly affected by air temperature & humidity. The fuel was also user friendly on the glow plugs used. The formula is; 80% nitro methane, 12% ethylene oxide & 8% lubricant. The lubricant is 2/3 Klotz Super Techniplate & 1/3 Blendzalls Racing Castor. The design of the steel roller rod allowed me to run much less lubricant than my competitors (18 to 20%) for the same size engine & to use an induction system never used before in a model boat engine. The induction system is called a bell valve. It was invented by an Australian speed flyer named Paul Bugl. From my dynamometer testing it proved to be the best induction system that could be used on a cantilevered crankshaft single cylinder engine. It increased the HP by .5 over other types of induction systems, including rotary valves, Zimmermen disks, inverted & standard drums. The valve is fully balanced, runs on a ball bearing & does not rub on any part of the back plate, which means it runs without friction. It also has the best time area numbers possible because the valves window is on the circumference of the back plate.

Jim Allen

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Niels Abildgaard on July 20, 2014, 04:01:38 PM
A picture of a Bugl drum inlet



http://modelenginenews.org/cardfile/gp2.html

kind regards

niels
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on July 20, 2014, 04:31:35 PM
Here are some photos of the Bugal valve. I also have in my possession one of the original HP 61 engines #456 manufactured by Hirtenberg. The engine was a gift from Don Jelhik. The engine is brand new, never run, in it's original box.

Notice that Bugal's valve is fastened to the crank pin & is made of aluminum in this version for the .15 cu in engine. Look carefully at what happens after the valve opens & remains open for a long period of time without any obstruction to the incoming flow. The hardened steel valve in my engine does the same thing. In fact it remains wide open without obstruction for 45* of rotation, without an early opening or late closing. What this does for the engines performance can not be understated. Bugal valves used in larger size engines were made of steel.

I am also very familar with Bugals hanger piston. His hanger piston design was used in Ed Kalfus' record setting .90 cu in tether boat engine. The hanger piston design makes it possible to balance a single cylinder reciprocating engine according to Ricardo's formula; 1/2 the repciprocating weight & all of the rotating weight should be used on the crankshaft's counter balance.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Admiral_dk on July 20, 2014, 08:02:19 PM
Hi Jim

Again thank you very much.

My Moto Cross bikes in my youth had honed hard chrome - I just forgot to think about it in my question. On the other side - if we ignore the lubrication part in my question, I wondered about the perfection of the surface. No worries - you answered that with your example of the crankpin.

I was under no illusion about your power figures and tuned pipe - there is no way you could reach those figures without. I'm guessing that the reason you create your pipes from turned steel are strength. Modern pipes for motorcycles has been hydro formed for years now - it's the easiest way to get the modern shapes without straight sides - this has given the last few HP's + a broader rev. range.
The last part of getting over revs (more revs than the pipe will allow) has come from ignition mapping - this allows a two stroke Moto GP bike that stops pulling a 12,000 RPM to continue to 14,000 RPM, It will not gain any more power up there, but it comes in handy in corners where you are leaned to hard over to change gear  ;)

That is a huge inlet "tract" for the size engine.

Best wishes

Per
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: dieselpilot on July 20, 2014, 08:45:52 PM
Chromed cylinders must be finished afterwards because the chrome builds up thicker near the corners of the ports. http://www.electro-coatings.com/effects-of-electroplating.php If you look closely at production liners you can see this.

Greg
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on July 20, 2014, 09:15:11 PM
Many things have changed over the years & are changing while we are talking. Most high performance pipes for two stroke racing motor cycles are welded up in prerolled sections. The material of choice is stainless steel because of its low heat thermal conductivity, followed by titanium, plain steel & then aluminum. Transfer geometry which was highly developed by Gordon Blairs work at Belfast University has also been changed by the work done by the engineers at Aprillia. Combustion chamber design for two strokes no longer revolves around only hemispherical type chambers. I presently use a toroidal chamber on my 26 cc tuned pipe gas engines. The engine, which has a cylinder bore of 1.339" (34 mm) & a stroke of 1.102" (28 mm), use a toroidal head where the ground strap of the spark plug is .015" away from the piston, when the piston is at TDC. THERE IS NO DETONATION problem when using the toroidal head button, yet it can double the compression that could be used with any hemi type head button!

Even chrome plated cylinders have changed to the better stuff developed by Mahle, which is Nikasil. Hard industrial chrome is certainly hard enough but it is not oleofilic. Many things have been tried to give chrome the ability to "WET" the surface with the lubricant present in the cylinder. Of course Nikasil is much more expensive but in high performance engines there appears to be a 2 to 4 % HP gain, because of the increased lubricity of the coating. Heat transfer is also greatly improved, by as much as 5 times.

My engines have a very good amount of over-rev power. The tuned pipes used, good time area numbers in the induction, transfer & exhaust tracks, plus my own carburetor design make this possible. Of course,  if the engine is not mechanically reliable tuning in this area will be impossible.

The photos show a typical toroidal head & the custom made spark plug (Lohring Millers idea) which has two ground straps coming from the sides. I have also included some typical welded tuned pipe sections. Since the area for ionization of the spark is exposed to the incoming charge by the advancing piston, a very powerful coil is needed to fire the spark. I have done extensive testing of the electronic Power Spark system which has ignition mapping, but still prefer the simplicity & reliability of a CDI magneto system.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on July 20, 2014, 09:25:14 PM
Chromed cylinders must be finished afterwards because the chrome builds up thicker near the corners of the ports. http://www.electro-coatings.com/effects-of-electroplating.php If you look closely at production liners you can see this.

Greg

Greg you are correct about the build up in these areas as well as the top & bottom of the cylinder. However, there will be much less of a build up if the fixture holding the cylinder is made of brass. This applies to the top & bottom of the cylinder also. You trick the chrome into thinking the cylinder ends someplace else. When using a brass sleeve, it should be relieved in the areas behind the ports. Failure to do this will make removal of the cylinder impossible.

Jim
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: JMcRae on July 21, 2014, 03:01:30 AM
Jim I was wondering what type of balancing you use with your engines, static or dynamic. I am sure at 30000+ rpm balance is a major factor and some what of a black art.
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on July 21, 2014, 12:51:03 PM
Jim I was wondering what type of balancing you use with your engines, static or dynamic. I am sure at 30000+ rpm balance is a major factor and some what of a black art.

In the beginning I attempted to use Ricardo's formula for balancing single cylinder two strokes. This work well for lower RPM engines (15,000 to 20,000) & engines that use a  hanger type piston. It doesn't work with piston boss type pistons & engine RPM's of 30,000+. I found that 33% of the total reciprocating weight plus the total rotating on the crank counterbalance allows the engine to run smoothly in the 20,000 to 30,000+ RPM range. The full disk crankshaft I used required the addition of two 5/16" OD Mallory metal slugs to get the balance where the engine ran the smoothest at WOT. Another cut & try experience.

JA
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: steamer on July 21, 2014, 01:28:16 PM
Welcome to the Forum Jim!   That's some mighty impressive work you have there!   

Following along....

Dave
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on July 22, 2014, 03:28:40 AM
If anyone is interested, I would take the time to explain in detail, with photos, about the automatic fuel metering carburetors used on these engines. The carburetors are 100% maintenance free & have been thoroughly tested & used for more than 23 years.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: v22 on July 22, 2014, 04:21:20 AM
Jim thanks for your contribution. This thread is absolutely amazing. I really like the photo of the connecting rods. Sure tells a story.

Is there any chance that you could start a thread on your dyno? I know there are a lot of people building their own IC engines that would love to know the power output. Information is a bit thin on the ground in this space.
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: PStechPaul on July 22, 2014, 04:59:17 AM
I am fascinated by the level of precision and effort put into these engines. It is far from anything I could hope to achieve, or even come close to, without perhaps a true passion for such pursuit of excellence. But on a more practical level, I might be interested in learning how to improve existing small two-cycle engines as found in chain saws and weed whackers. Maybe just some ideas on how to make a more reliable carburetor (which seems to be what usually goes bad) would be helpful.

It seems you have an immense amount of knowledge, and it is rather overwhelming to follow everything you have introduced in this thread. Perhaps breaking it down to some simpler concepts and components, such as the carburetor and the dynamometer, as has been suggested, in separate threads, would be easier to grasp and use (or at least attempt).

As for the dyno, I think a fairly simple and accurate instrument could be constructed using a set of reduction or speed increasing belts and pulleys, connected to a generator (such as a 2 HP treadmill motor) and a variable resistance load. The RPM can be read by a simple tachometer and the power can be determined by the actual DC current and voltage along with the previously measured (or estimated) efficiency of the generator.

I'll enjoy following along as best I can, but it would be more fascinating to see some videos, if you could post them.

Frankly I am much more interested in electric motors, controllers, and energy storage devices (mostly batteries), as I believe these will be the prime movers of choice (and economic necessity) in the near future. But there will probably always be some applications that cannot be achieved in any other way than some form of heat engine using internal or external combustion. And along with that, it would be interesting to know the efficiency of high performance engines such as those you design.

Thanks for your valuable contributions.
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: ozzie46 on July 22, 2014, 12:57:15 PM
If anyone is interested, I would take the time to explain in detail, with photos, about the automatic fuel metering carburetors used on these engines. The carburetors are 100% maintenance free & have been thoroughly tested & used for more than 23 years.

Jim Allen

By all means lets hear more on the carbs. Carbs come up often. And welcome to the forum.
 Fantastic work there.

 Ron
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: rockknocker on July 22, 2014, 03:30:05 PM
Thanks for sharing the details on your dyno setup! I look forward to your next post!
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: dieselpilot on July 22, 2014, 03:49:32 PM
As for the dyno, I think a fairly simple and accurate instrument could be constructed using a set of reduction or speed increasing belts and pulleys, connected to a generator (such as a 2 HP treadmill motor) and a variable resistance load. The RPM can be read by a simple tachometer and the power can be determined by the actual DC current and voltage along with the previously measured (or estimated) efficiency of the generator.

This all depends on how accurate you want to be. The generator load is the normal way to do it, but dealing with losses in the reduction and the generator itself is too much trouble. It's much easier to measure torque directly.

Greg
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: ttrikalin on July 22, 2014, 04:00:53 PM
If anyone is interested, I would take the time to explain in detail, with photos, about the automatic fuel metering carburetors used on these engines. The carburetors are 100% maintenance free & have been thoroughly tested & used for more than 23 years.

Jim Allen

Jim
more information for the info hungry newbies like me would be much appreciated!
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: tvoght on July 22, 2014, 04:10:41 PM
It's my understanding that even the dynos that use generators will have the generator mounted in gimbals with an arm connected to the generator casing for direct measurement of torque. The generator is just a braking device and the measured output power is of no concern as far as engine data collection  is concerned.

Manufacturers testing a lot of large engines will sell some of the testing power into the grid to mitigate fuel expenses.

--Tim
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Roger B on July 22, 2014, 05:44:22 PM
If anyone is interested, I would take the time to explain in detail, with photos, about the automatic fuel metering carburetors used on these engines. The carburetors are 100% maintenance free & have been thoroughly tested & used for more than 23 years.

Jim Allen

Jim
more information for the info hungry newbies like me would be much appreciated!

I agree  :ThumbsUp:  :ThumbsUp: Carburation is one of my current problems  ::)
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on July 23, 2014, 03:34:52 AM
Right now I'm loaded up with work again, nothing new. Please be patient.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on August 10, 2014, 02:21:29 PM
The carburetors I build & use do not have any type of venturi & therefore no vacuum signal to deliver the necessary amount of fuel. There are no diaphragms to be replaced, filters to clean, fulcrum arms, pop-off springs to adjust or butterfly plates. Fuel metering is done automatically after setting the single high speed needle. Since there is no vacuum signal, due to the straight through, large ID, carburetor bore, the fuel system must be pressurized. More than adequate pressure comes from the engines tuned pipe in the amount of 120 inches of water (4.36 psi) at WOT. The amount of pressure varies directly with the engines RPM's.

The automatic fuel metering is accomplished with two internal parts, one which is stationary & has a "V" shaped slot. It is located on the left hand side of the first photo along with the needle valve. The second part, which is a tube, fits over the "V" shaped slot. As the barrel is rotated, the "round hole" in the tube closes of the "V" shaped slot & meters the fuel automatically. The rotating barrel's end points, full open & full closed positions, are controlled with a pin mounted in the side of the barrel. The pin engages the plate seen in the bottom right hand of the first photo.

All the internal parts of the carburetor are made of 303 stainless steel. The needle valves have precision ground tapers & are made of 52100 full hard steel gauge pins. The photos show the fixture used to bore the carburetor's bore (.625") & drill the hole for a .0625" dowel pin which holds the rotating tube in place. The rotating metering hole engages the "V" slot exactly & this same piece has a threaded end to mount the throttle arm. Also shown is the fixture used to make & bend the needle valve's retaining spring. The retainers are made of #172 beryllium copper which is fully hardened. The last fixture is used to cut the "V" slot in the stationary piece. The "V" shaped slot is cut very deep in this piece & it could not be done without the fixture.

These carburetors have proved themselves to be 100% maintenance free & highly wear resistant. They can be used with gasoline as well as nitro methane based fuels.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: gbritnell on August 10, 2014, 05:00:35 PM
Jim,
I've been following your thread and your work is first rate. I appreciate your photos and explanations. Having built miniature I.C. engines for a good number of years I have played with many types of carbs. I do have a very sophisticated O.S. carb that has a similar setup of which you describe. It has a small tapered slot around which the barrel rotates to control fuel flow through the idle and mid range. It also has needles to help assist in low, medium and high fine tuning.
For my type of work the biggest problem I see is trying to calculate the required slot taper and the amount that the barrel has to rotate to uncover a given area of fuel flow.
It's a very simple setup for your purposes using the 2 stroke pulses to pressurize the fuel system which is common to RC engines but I'm afraid trying to adapt this to my small 4 cycle engines would actually involve more complexity than what I currently use.
It does give me more insight into other systems being used, thanks.
gbritnell
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on August 10, 2014, 06:21:34 PM
Jim,
I've been following your thread and your work is first rate. I appreciate your photos and explanations. Having built miniature I.C. engines for a good number of years I have played with many types of carbs. I do have a very sophisticated O.S. carb that has a similar setup of which you describe. It has a small tapered slot around which the barrel rotates to control fuel flow through the idle and mid range. It also has needles to help assist in low, medium and high fine tuning.
For my type of work the biggest problem I see is trying to calculate the required slot taper and the amount that the barrel has to rotate to uncover a given area of fuel flow.
It's a very simple setup for your purposes using the 2 stroke pulses to pressurize the fuel system which is common to RC engines but I'm afraid trying to adapt this to my small 4 cycle engines would actually involve more complexity than what I currently use.
It does give me more insight into other systems being used, thanks.
gbritnell

You are totally correct about what method, system or device can be used to effectively meter the fuel from low throttle to WOT. The "V" shaped slot (60 * included angle) with its matting hole increase & decrease the fuel at an exponential rate. This feature allows the engine to throttle up & down without any hesitation, lagging or stumbling. I purposely have not talked about what can happen when the fuel system is exposed to high "G" forces as the boat is turned at speed & when there is no consideration of the placement of the fuel tank in relation to the carburetor.

JA
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on August 20, 2014, 03:28:28 PM
For several years I have been testing carburetors without fuel metering, no diaphragms, no butterflies, no choke plates, no metering circuits, no pop-off springs, no filtering screens & only one needle to adjust, but with a needle valved controlled air bleed system which prevents the carburetor from loading up at low throttle settings. Opening the air bleed circuit at the correct time is critical as well as controlling the amount of addition air that is necessary to prevent the engine from going to a rich setting & eventually flooding out. Since there is no obstruction of any kind (butterflies, choke plates, metering tubes or fuel delivery tubes) in the incoming air stream, maximum air flow through the carburetor's .625" bore is easily possible. The same features of the the .625" bore automatic fuel metering (100% maintenance free, extremely reliability & wear resistance) are found in the .625" bore air bleed type carburetor. Throttle response from 3,000 to 22,000 RPM is instantaneous. The necessary amount of fuel to be delivered to the carburetor is a function of the pressure developed in the custom designed tuned pipe. The entire fuel system is pressured & that pressure follows exactly the engines RPM's.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Admiral_dk on August 20, 2014, 08:46:08 PM
Another amount of great information and pictures - thank you very much  :praise2:

Best wishes

Per
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on August 21, 2014, 02:34:00 PM
Construction of the tuned pipes used on both the gas & nitro methane powered engines are machined from solid bar #1018 cold rolled steel. A typical wall thickness of .020", with .010" at the joining points of the overlapping  sections, which are silver soldered, gives a chamber that is precise & very smooth inside. Silver soldering is done while the tuned pipe is slowly rotating between centers in the lathe. Tuned pipes are painted with, baked on, high temperature exhaust paint. There will be no discussion of the technical aspects of the tuned pipes or how they work. I will say that just about any tuned pipe will work to increase the engine's HP. However,  there will be only one tuned pipe capable of increasing the engine's HP 45 to 50% at a particular RPM range. Finding that tuned pipe is not easy!

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on August 22, 2014, 01:39:28 AM
I have no idea where to begin when discussing the hydraulic dynamometer. Maybe if some engine builders out there posted questions we could begin this discussion. As a start this water brake is modeled after the Kahn, single perforated disk, hydraulic dynamometers. It uses a sealed housing mounted in a Rulon lined trunnion type mount. Rulon is used because it has the lowest stick slip rating of any known material. Using sleeves for the trunnion bearings in place of ball or roller bearings helps dampen vibrations & also gives a very high load carrying capability to the trunnion mount. Align boring of the trunnion sleeve bearings was done after both ends of the mount were fastened & doweled pinned.

More to come.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on August 23, 2014, 12:15:28 PM
The dynamometer's housing, which can rotate freely in it's Trunnion mounts, is very precisely machined & requires no type of sealing ("O" rings, gaskets or sealing compounds). Sealing is accomplished with an interference fit of the two housing pieces & 16, 6-32 SHCS. Machined holes or pockets in the rotor & the housing inside faces create an annulus as the rotor rotates, which is rotating at approximately half of the angular rotor's speed. The resulting drag created by the annulus formed applies a resisting force to the rotors rotation & an equal force to turn the dynamometer's housing.

The very high centrifugal force which results from this process forces the hot water out of the housing through the metering valve shown in the photo. The precisely machined, double sealed, outlet valve controls the amount of water (size or depth of the rotating water annulus) & therefore the amount of power that can be absorbed. This feature allows the dynamometer to apply infinitely variable loads the the engine. A water reservoir, which maintains a constant pressure, supplies incoming cold water to the dynamometer's housing from both sides of the rotor.

The rotors in my dynamometer are machine from 7075 T-651 aluminum. Rotors used in larger size hydraulic type dynamometers would be made of hardened stainless steel. They would be Blanchard ground & the entire rotor assembly would be dynamically balanced. A hardened stainless steel rotor provides superior resistance to corrosion & cavitation erosion.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on August 23, 2014, 12:23:24 PM
Additional photos..................
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: smfr on August 23, 2014, 05:04:16 PM
Fascinating stuff, Jim. Keep it coming  :ThumbsUp:

Simon
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Roger B on August 26, 2014, 07:13:09 PM
Interesting stuff, thank you.  :ThumbsUp:  :ThumbsUp:  To my understanding you are really using fuel injection rather than carburation. The fuel flow is set by the engine RPM (exhaust pressure).  :headscratch:
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on August 29, 2014, 01:41:04 PM
Roger,

I don't think the "very simple system" I'm using would qualify as a fuel injection system.  I am aware that a fast enough, fuel injection system with small injectors, that could keep up with engine RPM's from 22,000 to 30,000, does not exist. I guess my system could be described as a continuous indirect injection system with some measure of fuel metering. Injectors, operating under high pressures, deliver very small fuel droplets that can be easily atomized. My system is dumping fuel into the incoming air stream under the maximum pressure of 120 inches of water (4.336 psi). A fuel injector could inject the fuel at 2.5 BAR (36.259 psi).  One advantage of injecting in the intake tract is the big end connecting rod bearing is lubricated & cooled by the fuel spray.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: lohring on August 29, 2014, 06:00:31 PM
Tuned pipe pressure to the tank has been the standard in glow ignition engines for a long time.  Crankcase pressure has also been used, most successfully with a pressure regulator.  The use in a gasoline fueled engine is a lot less common due to the readily available carbs like the Walbro.  However, at high rpm the pumper carbs can't keep up.  We have had consistent problems in our straight line record engines that turn over 20,000 rpm.  Jim's "simple" system avoids this issue and feeds fuel proportionally with the pipe pressure.  Pipe pressure is related to power, so in the system can be adjusted to work well.  However, it's not as fool proof as the pumper carbs for low performance, industrial engine use.

Lohring Miller
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Roger B on August 29, 2014, 08:21:26 PM
My thought was that the fuel flow is controlled by the exhaust pressure (load) rather than the manifold depression. Some simple single point automotive fuel injection systems had a continuous flow into the entrance to the manifold rather that pulsed injection by each valve.
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: karolh on August 29, 2014, 08:26:37 PM
Absolutely amazing and impressive work and all I can say is wow. So very glad that I found this thread. Please continue to share your outstanding work with us.
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Jo on August 29, 2014, 08:52:23 PM
Hi Karol,

Any chance of posting an introduction to yourself and your modelling interests in the introduction section?

It will let the other members get to know you and they may be able to help you in the future  ;).

Jo
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: karolh on August 30, 2014, 02:06:03 AM
Hi Karol,

Any chance of posting an introduction to yourself and your modelling interests in the introduction section?

It will let the other members get to know you and they may be able to help you in the future  ;).

Jo

Will do.
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on August 30, 2014, 02:00:13 PM
Tuned pipe pressure to the tank has been the standard in glow ignition engines for a long time.  Crankcase pressure has also been used, most successfully with a pressure regulator.  The use in a gasoline fueled engine is a lot less common due to the readily available carbs like the Walbro.  However, at high rpm the pumper carbs can't keep up.  We have had consistent problems in our straight line record engines that turn over 20,000 rpm.  Jim's "simple" system avoids this issue and feeds fuel proportionally with the pipe pressure.  Pipe pressure is related to power, so in the system can be adjusted to work well.  However, it's not as fool proof as the pumper carbs for low performance, industrial engine use.

Lohring Miller

Recent test have shown that a tuned pipe pressurized system, without any fuel metering, can operate at low performance levels as well as very high RPM levels. A key factor in this system is the needle valved controlled air bleed circuit similar to the type that GBritnell used on his barrel type carburetor. Control of the amount of air added as the barrel is closing & control of the exact time when the air is added is required for proper operation. When both are done correctly the engine can idle indefinitely at 3,000 RPM & accelerate instantly, without hesitation or stumbling, to 22,000+ RPM. Even though the engine can sustain a continued low idle of 3,000 RPM, the lowest operating RPM needed when operating under load is 9,000 RPM. An additional important feature of this system is the high performance sparking coil used which can fire a spark across a .040" gap. Most engines of a 26 cc to 35 cc size will run spark plug gaps of .015" to .020".  I run a .025" to .030" gap which gives a longer duration spark. Also the spark plug wire used is a low resistance, stranded copper conductor 8 mm in size with high performance connectors at both ends. I make the ignition wire used & crimp the connectors with a special tool. A special digital multi-meter tells me the resistance of the spark plug wire is much less than .1 ohm.

Jim Allen

Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: lohring on August 30, 2014, 03:32:11 PM
I see the air bleed needle under the barrel.  I have your detailed pictures and sketches, but I bet others would like more information on exactly how this all fits together and works. 

Lohring Miller
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on August 30, 2014, 04:58:49 PM
I'll try to take more photos of the air bleed track itself. It is a separate part that attaches to the carburetor body with 4 of  the existing 8,  2-56 screws. The part's outlet opens into the 1/8" diameter hole in the carburetor's body. The position & size of the air bleed hole was found through trial & error. For this engine, with this pipe & this .625" bore carburetor, the air bleed begins to open just past 1/2 throttle closing. 7 degrees beyond this point the air bleed hole is 1/2 open.  The amount of air being admitted is very sensitive in controlling the engine at lower throttle settings. If there is to much additional air being admitted, then engine will begin to rev up as the carburetor barrel is closed below 1/2 throttle. If there is not enough air, then the engine will load up & stop running.

I am guilty of not making detailed prints because they are not needed when machining most parts. I make partial sketches with important numbers & usually begin cutting using thoughts in my mind. The posted photo shows the exact position & size (.1250") of the air bleed hole on the carburetor presently being used. In the first photo, if you look carefully, the black dot at the bottom of the carburetor's bore adjacent to the rotating barrels edge, is the air bleed hole. Its size & position are very similar to a .725" bore carburetor being tested which uses the same type of air bleed system. Many people say the air bleed system can not work over a wide range. In my opinion, from many hours of in depth testing, they are completely misinformed.

Jim Allen 
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on September 07, 2014, 06:45:05 PM
The engine's power is absorbed & converted into heat by the water vortices created between the rotor & the housing holes. The resulting drag applies a resistance to rotation & with an equal effort turns the dynamometer housing mounted in the trunnion bearings. The distance from the center of the dynamometer housing to the center of the load cell is exactly 6.000". Since the torque arm's movement is only .005", there is no tangent error to consider when reading torque amounts. Notice the lightening slots machined in the torque arm. This small amount of out of balance causes the dynamometer housing to rotate in the very low stick slip, Rulon bearings, which were aligned bored after the cradle was assembled. The calibrated Omega model LCF load cell with a + or - 5 lbs. range & a safe overload of 150% is not fastened to the torque arm. The special designed ball adaptor sits on the load cell's stud to prevent errors which could be caused by any misalignment. The ball adaptor also has a screw thread on its top end, which allows weights to be attached for accuracy checks, after zero setting the load cell at the digital meter. Notice the very rigid mounting of the load cell's solid one piece machined base which ensures rigidity & squareness to the dynamometer housing. The load cell base can be adjusted up & down to allow the torque arm to be adjusted perpendicular to the load cell axis. The cost of the calibrated load cell was approximately $550.00 dollars. The digital panel connected to the load cell reads the applied force in lbs. to two decimal points & it is shock mounted. Its cost was approximately $650.00 dollars.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on September 14, 2014, 11:04:48 PM
One of the most important mechanical parts of any engine test stand is the type of universal used to transmit the engine's HP. Constant velocity, mechanically reliable universals will become necessary because it will be impossible to perfectly align the various rotating parts. I machine the precision ball & pin type universals seen in the photos. All the male ball ends & the slotted female ends are machined from heat treated AISI 0-1 tool steel. The drive pins are made of hardened M-2 steel reamer blanks.

A detailed explanation of  how to make these pieces will follow. They have been tested on various engine test stands as well as on actual models at speeds above 32,000+ RPM & 7.5+ HP.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on September 28, 2014, 03:09:33 PM
I have received several e-mails with questions about how to hard chrome plate engine cylinders for use in high performance two stroke engines. There are two basic material types presently being used, aluminum & brass.  Both can be efficiently & easily plated with properly designed fixtures in the basic chromic acid/sulfate bath. Finishing of chrome plated cylinder bores needs to be done by honing or grinding. Precise measuring of the bore's taper & the bore's roundness is also necessary. Honing & measuring can be done with standard types of Sunnen equipment.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: WingRacer on September 28, 2014, 03:20:32 PM
Thx you Jim for your post!

Roy
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on September 28, 2014, 04:17:42 PM
One important part of the chroming tank is the lead antimony anode. It needs to be placed in the center of the cylinder's bore to ensure that an equal amount of chrome is plated on the cylinder's ID. Chrome tanks have very poor throwing ability which means a very high current density & closeness of the anode to the part being plated are necessary. The photos show the casting mold & the finished machined lead antimony anode positioned on center by the PVC fixture. At a current density of 3 amps/ sq in (total of 24 amps), the tank will give .0012" of chrome/ side/ hour in 2 hours. Also, the bath must be maintained at 125* to 135* F.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on September 28, 2014, 06:51:56 PM
The outside brass sleeve, which the cylinder sits in, makes positive contact between the two stripped cathode wires & the cylinder. The large clamping nut & the top brass ring clamp all the pieces together securely. The outside brass sleeve is also relieved in it's ID in the areas where the cylinder's windows are. This is necessary because there will be a small build up of chrome in these areas making removal of the cylinder impossible. All pieces are machined as a slip fit.

Another reason that the outside brass sleeve & the top ring are necessary is that they prevent the chrome from building up at the top & bottom edges of the cylinder's bore. Any chrome plated on the bottom & ID of the outside brass sleeve as well as the ID of the top ring can be removed with a 50% solution of hydrochloric acid.


Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Admiral_dk on September 28, 2014, 07:07:23 PM
Even though you showed (most of) these pictures before, I would like to thank you for sharing your knowledge with the rest of the world (or at least those of us following this thread  :praise2:
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Roger B on September 28, 2014, 07:18:17 PM
I think that there are a lot of people following this thread, but in my case it is so far advanced I struggle with some of it  ::) There is still at lot to learn though  :) Please keep posting  :cheers:
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on September 28, 2014, 11:18:39 PM
If anyone is interested, the hard industrial chroming of aluminum cylinders will be explained in detail. This is presently being done on the 4032 aluminum sleeves used in all the Nelson Q-40 pylon racing engines. The process involves several different chemicals with the same type brass fixture, PVC holding fixture & CrO3, H2SO4 bath. The chrome plated on aluminum is as hard ( approximately 1100 Vickers) as any plated on a steel or a brass piece. The only real difference is in the cleaning & etching processes involved.  Many engine manufacturers have given up on chroming aluminum cylinders because of this.

Jim Allen

Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Admiral_dk on September 29, 2014, 07:56:05 PM
Oh yes please !!!!

Will it make any difference with different aluminium types / any to be avoided ?
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on September 30, 2014, 02:47:19 AM
I have not chromed different aluminum types, but I think there will not be any problem if the procedure is done properly. This is also true for different types of brass or bronze alloys. I will "CAREFULLY" write up the procedure & post it sometime this weekend. There are several chemical solutions that must be used with specific time amounts for each solution before placing the cylinder in the chroming fixture. Washing is done with Dawn dish washing detergent & hot water.  If done properly the chroming can be done without any blistering or pitting. Aluminum sleeves that are not chromed properly can only be saved by grinding all the chrome off.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on October 17, 2014, 04:48:22 PM
I have successfully hard chrome plated 4032 aluminum cylinders, 360 free machining brass, 544 phosphorous bronze & steel parts in the standard, basic 100 to 1 chromic acid/sulfate bath. The following chemicals & procedures have been used for more than 25 years to hard chrome plate 4032 aluminum cylinders. Chemicals & solutions for chroming aluminum must be stored in polypropylene jars with polypropylene covers. A well ventilated room, a removable filter type oxygen mask & rubber gloves should also be used when chroming. The chrome tank itself, which will contain heaters, a liquid measuring thermometer & a exit hole for the cathode wires will be sealed during the chroming process.

The mixing of all chemicals should be done with a protective rubber apron, rubber gloves & a face splash shield. All chemicals are mixed by volumes in their particular ratios.

1. Mix hydrofluoric acid & nitric acid in a 1 to 3 ratio by volume.
2. Mix nitric acid & water in a 1 to 1 ratio by volume
3. Mix zincate & water in a 2 to 1 ratio by volume.

The procedures are as follows;

1.With rubber gloves on, clean the cylinder's ID twice with Dawn dish washing soap & hot water. Use a round nylon brush to scrub the cylinder's ID. While holding the cylinder, only on its "OUTSIDE", with a formed aluminum wire, place the cylinder & aluminum wire holder in the hydrofluoric & nitric acid solution for 30 seconds. Agitate the piece & solution together. Remove & rinse in hot water.
2. Place the cylinder with formed wire in the zincate & water solution for 60 seconds. Agitate the piece & solution together. Remove & rinse in hot water.
3. Place the cylinder with formed wire in the nitric acid & water solution for 5 seconds. Remove & rinse in hot water.
4. Place the cylinder with formed wire in the zincate & water solution for 90 seconds. Agitate the piece & the solution together. Remove & rinse in hot water.
5. Place the cylinder, with it's brass holding fixture, in the preheated chrome tank after attaching the anode (positive) & the cathode (negative) contacts. All connections "MUST" be positive, solid connections. With the power turned on, place the entire fixture in the chrome tank. The current should immediately begin to read!! Use the half current amount for approximately 8 to 10 minutes & then the full current amount for 90 minutes. The full current amount is calculated from the total area of the cylinder & it's brass holding fixture, divided by the current to give 3 amps/ sq in.

With a lead antimony anode of 1/4" diameter, the tank should be able to put on .001" to .0015" of chrome/ side. Improper cleaning, etching or bad contacts will result in blistering, pitting or poor deposit thickness. If done properly, with a bath temperature of 125* to 130* F, a current density of 3 amps/ sq in, the plating should be approximately 950 to 1,025 Vickers. This means the plating can not be cut with any type of carbide tooling!

More detailed pictures to follow & possible a video, if time allows this.

Jim Allen


Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Roger B on October 18, 2014, 08:23:07 PM
That's some serious effort  :praise2: Still following and learning  :ThumbsUp:
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Admiral_dk on October 18, 2014, 10:51:35 PM
I'm with Roger - serious stuff and serious precautions.

Quote
With a lead antimony anode of 1/4" diameter, the tank should be able to put on .001" to .0015" of chrome/ side.

Ohh - I got that wrong previously - I thought that the anode touched the cylinder walls.

Again thank you very much.
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on October 19, 2014, 12:15:00 AM
I'm with Roger - serious stuff and serious precautions.

Quote
With a lead antimony anode of 1/4" diameter, the tank should be able to put on .001" to .0015" of chrome/ side.

Ohh - I got that wrong previously - I thought that the anode touched the cylinder walls.

Again thank you very much.

One of the characteristics of any hard chrome plating tank is the inability of the system to plate when the distance between the lead antimony anode (positive) & the desired surface to be plated, the cylinder's ID (cathode), is large. For example, the ID of the cylinder bore which uses the 1/4" OD anode is approximately .805".  When plating a 1.125" ID cylinder bore, a 5/8" OD anode is used. One reason for this is because the standard, chromic acid/ sulfate bath, is not very current efficient. This means approximately 14% of the electrical energy is used to plate the chromium & 86% is wasted. It also means that the plating process is slow but reliable. The solution is relatively easy to make, analyze, & control with economical, of the shelf chemicals.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Admiral_dk on October 19, 2014, 11:35:11 PM
Hi Jim

Thank you for your answer.

Let me see if I got this info right. In the first example, you got 805-250 = 555 mill clearance and in the second, you got 1125-625 = 500 mill clearance between the anode and the cylinder wall. Does that mean the I should aim for some 500 mill (") of clearance if (and when) I try to do some hard chroming ?

Does that clearance apply to all sizes ? - I'm asking because I might be tempted to do a bigger engine if I got success with the small size (though admittedly not in the near future - I need to start on the small engines first, but one can dream) ....

Best wishes

Per
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Allen Smithee on October 20, 2014, 12:09:58 AM
Your "clearance" figures should be half that because the bore and anode dimensions are diameters, where the clearance is a radius.

AS
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on October 20, 2014, 12:31:51 AM
Hi Jim

Thank you for your answer.

Let me see if I got this info right. In the first example, you got 805-250 = 555 mill clearance and in the second, you got 1125-625 = 500 mill clearance between the anode and the cylinder wall. Does that mean the I should aim for some 500 mill (") of clearance if (and when) I try to do some hard chroming ?

Does that clearance apply to all sizes ? - I'm asking because I might be tempted to do a bigger engine if I got success with the small size (though admittedly not in the near future - I need to start on the small engines first, but one can dream) ....

Best wishes

Per

The distance between the anode's OD & the cylinders ID is 1/2 the total diameter distances or approximately .250" of clearance. You will want to make this distance as small as possible & still allow for an adequate space for the chromic acid/ sulfate solution. For larger diameter bores it will be necessary to have several anodes or a machined cast anode. The anode could also be made in the form of a hollow cylinder closed at both ends. The anode I use for the 1.125" bore is cast in a mold & then machined to size.

The length of the anode with respect to the length of the cylinder to be chromed should not be longer or shorter in length. In this case, the anode must be longer to facilitate its mounting in the PVC sleeve. The addition of the outside brass sleeve, which extends below the bottom of the cylinder & the brass top piece, which extends above the top of the cylinder,  prevents the common dogbone effect (build up of chrome) that could takes place at the top & bottom edges of the cylinder without the brass pieces in place, since the anode is longer than length of the cylinder being chromed.

The PVC outer shell electrically insulates the anode from the cathode (cylinder) & positions it dead on center. The large lip on the top of the brass sleeve (cathode) sits directly on the two cathode wires. It is clamped into position with the top brass ring & the square PVC nut using a large amount of force.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Admiral_dk on October 20, 2014, 06:32:08 PM
Thank you very much for clarifying that.

As for my wrong use of the word clearance - sorry, but being dyslexic and not having English as first language is bound to get some errors in my writing from time to time.  ::)
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on October 20, 2014, 08:44:24 PM
I am planning a detailed explanation of how to make a very rigid, high mechanically reliable, wear resistant, three piece split or cantilevered type crank shaft for use in 7.5 to 30 cc size engines, operating at very high HP (7.5+) & RPM (30,000+) numbers. Metallurgy, fixtures, heat treating & machining techniques make it possible to produce very high quality crankshafts on manual machines with manual tools. The top two photos show two piece & three piece, pressed together crankshafts & one of the fixtures used to grind crank pin holes in the lathe, using a Themac tool post grinder. The ground crank pin holes ID's, are square to the crankshaft's journal, in two axes, with in .0002" total indicator run out, over 6.000" distance. Press fit amounts of the crank pins in their ground holes for both types are .0013"+. No crankshaft failures (cracking or twisting) thus far. Also, pressed in pins allow for the replacement of any worn crank pin, giving the assembled piece an infinite life.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on November 15, 2014, 05:53:29 PM
Crankshafts that are to be used in high HP, high RPM,  miniature two cycle engines (2.5 cc to 30 cc) are usually made of 8620 or 9310 steel which is case hardened. However, there may be other types of steels that are used by Eastern manufacturers. These crankshafts can be one piece cantilevered types, two piece cantilevered types or three piece split types. From left to right in the photo; the first two one piece cantilevered crankshafts made of 8620, case hardened tool steel, had their .2812" diameter crank pins sheared off. The next three cantilevered crankshafts (two piece types) made of 9310 tool steel also failed when their .3125" diameter, pressed in crank pins, sheared off. Both types were .3750" X .5000". All two piece crankshafts use crank pins made of M-2 full hard tool steel. The press fit amount used is .0013" to .0015" & all crank pin holes have their ID's ground.

The last two crankshafts are made of AISI S-7 through hardened tool steel, with .3281" diameter (M-2 steel) crank pins. They have never failed. The AISI S-7 tool steel is through hardened in standard hardening oil & tempered at 600* F followed by air cooling at room temperature. The crank pin hole is carefully ground, after tempering, to give a .0013"+ interference fit. The hole is ground square within .0002" in two axes for a distance of 6.000".  The shock resisting S-7 tool steel at this temper has a tensile strength of 285,000 psi; a yield strength of 220,00 psi; a hardness of Rc 54 & a Charpy impact value of 219 ft lbs.

More to come.

Jim Allen



Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Roger B on November 15, 2014, 06:27:52 PM
I'm still following with a lot of interest and some amazement  ::)

Some of the crank discs are left round with balance slots cut with something like a woodruff cutter. Does this offer advantages over the more conventional 'scalloped' designs?
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on November 15, 2014, 08:28:20 PM
Roger,

In depth constant load type dynamometer testing told me that dog bone type crankshafts make less HP than full disc crankshafts in the engines I build, especially in the over rev range. This may not be true in all engines. However, full disc type crankshafts, with slots cut with a woodruff cutter, are more rigid than dog bone types, but they require the addition of Mallory metal slugs to get the counterbalance amount correct. I balance at 33% of the total weight of the piston, wrist pin & connecting rod assembly. This overbalance condition has very small second harmonic vibration issues & it does increase the crankshaft's inertia, which has several advantages to be explained latter.

Many of the problems with high HP, high RPM engines originates with aluminum crankcase flexing. I use full a hard AISI O-1 tool steel front end with my custom made ceramic hybrid bearings fitted. The crankshaft is designed so that it is mechanically fastened to the inner race of both front bearings. A sleeve which fits over the crankshaft fastens both inner races of the front bearings together once the flywheel is bolted in place. The front end's seal is machined onto that same sleeve. Crankshaft end play is set at .003" to .004" axial play with machined spring steel washers of various thicknesses. Even at elevated temperatures, the end play remains the same because all the parts; the crankshaft; the sleeve; the shims; the front end & the bearing races, ARE ALL MADE OF STEEL!  This type front end runs faster & longer than any aluminum setup.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Roger B on November 16, 2014, 07:25:42 AM
Thank you for the explanation. Is 'Mallory metal' some type of heavy tungsten alloy?
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on November 16, 2014, 01:30:27 PM
Mallory metal is machinable carbide. It is commonly used by engine builders to balance crankshafts. It can be purchased in different diameters & lengths ready to be used or machined to size as needed. The pieces in the photos are 11.18 mm (.440") diameter X 20 mm (.784") long & weigh 33.2 gms (1.171 ozs). They are machined shorter in length & peened in place on both sides of the crankshaft to prevent movement. Mallory metal is expensive! The 9 pieces shown in the photo cost approximately $70.00.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Roger B on November 16, 2014, 07:07:45 PM
In a previous job we used a tungsten alloy just called 'heavy alloy' for collimators for industrial X Ray sets (up to 15 Million volts). It certainly was heavy and also expensive. I wondered if this was something similar.
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on November 16, 2014, 07:42:47 PM
Mallory metal is primarily a Tungsten (W) alloy with a little copper (Cu) & nickel (Ni). Tungsten by itself is very difficult to machine. This is the reason for creating an alloy which is very dense but machinable. In fact it is denser than lead. The high cost is due to the tungsten content. I believe there are two metals that would be more dense than Mallory metal; depleted uranium & gold. Wonder how much it would cost for a few slugs of these?

Jim

Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Roger B on November 16, 2014, 07:50:45 PM
DU may not be so expensive as it is effectively a waste product from the current nuclear industry. It is used for shielding isotope X Ray cameras and also as ballast weights in some aircraft.
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Allen Smithee on November 17, 2014, 02:42:36 PM
DU may not be so expensive as it is effectively a waste product from the current nuclear industry. It is used for shielding isotope X Ray cameras and also as ballast weights in some aircraft.

Many years ago DU was used for ballast weights in aviation (mainly for mass-balances and inertial dampers in control systems where the balance arm had to fit into the smallest possible space) but civil aviation went through a programme of eliminating DU after scares about contamination after a couple of crashes, most notably El Al Flight 1862 at Amsterdam in 1992. The concern isn't over radiation - DU (like plutonium and many other heavy metals) is extremely chemically toxic (swallow or inhale a few grammes of powdered plutonium and the poisonous effects will kill you long before the radioactivity can do any damage).

Military aviation had been eliminating DU from aircraft for many years prior to this due to concerns over the toxic hazard to maintenance crews working on battle-damaged aircraft, and these days it's extremely rare to find any in use as ballast in a military aeroplane. You still find it in some kinds of cannon rounds, of course.

AS
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on November 17, 2014, 03:01:30 PM
Very good information to be aware of Allen. Even though it is not written in Latin, the information could be profound in some situations!

JA
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Allen Smithee on November 17, 2014, 04:13:17 PM
"I have been led to understand" (if you catch my drift) that there are two F-16s and an A-10 which suffered AAA damage to DU components during GW1 which were buried in the desert rather than repaired for this very reason.

AS
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on December 09, 2014, 03:37:09 PM
The dedicated fixture in the first two photos is used to grind crank pin holes in through hardened crankshafts. A Themac tool post grinder is used in the lathe to do this. The fixture is accurate to .0002" squareness in two axes for 6.000".  I have already stated the mechanical properties of the AISI S-7 tool steel to make these parts. The fixture could also be used to grind a one piece crankshaft's crank pin & it assures that every crankshaft is the same. The second fixture uses the hole on the left side to hold & machine the crankshaft's counter balance area when used in the milling machine. The hole in the right side has the finished ground crankshaft's OD as it's ID. It holds the crankshaft to allow the crank pin hole's ID to be ground, after mounting the fixture to the lathe face plate with dowel pins. Sometimes a Yuasa air turbine gig grinder is used for this operation.

The making of a machined retainer, with rollers, that can survive in very high HP, high RPM engines WITHOUT FAILING!

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: petertha on December 23, 2014, 02:43:13 AM
Hi Jim. Sorry for the dumb question. I read through the entire post a few times & still at a loss to visualize your method to finish the chromed liner. You mentioned a few points that caught my eye & attached (what I think) to be a fixture related to the operation. But how exactly is it used? 'Grinding' (to me) conjures an image of a powered rotating abrasive tool brought against the part. Is there a motorized aspect to this? What does the business end of the grinding tool look like? How do you preserve the pre-chromed taper angle during finishing? Thanks in advance! -Peter

(reply 3)
- No lapping compounds of any kind, including non-embedding types, should ever be used to fit a piston in ABC or AAC engines
- Cylinders are machined with their taper amount & then chrome plated with approximately .0015" thick chrome/ side
- The cylinders are then ID ground
(reply 35)
- Cylinders in nitro engines such as the Nelson are honed on a Sunnen honing machine to give a fine finish in a short amount of time.
- Cylinders in my .90 cu in engine are ground & will have an even better finish than honing


Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on December 24, 2014, 02:33:04 PM
Definitely NOT a dumb question! I'll review the incomplete explanations given & explain in detail how this can be easily done in the lathe with a tool post grinder. The accurate setting of the compound's angle can be done without the use of a sine bar & gauge blocks.The photos show the grinding of a tapered split collet's seat after setting the compound with a "taper master". A similar procedure is done for grinding the chrome plated tapered cylinder ID.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: dieselpilot on December 28, 2014, 04:15:43 AM
Jim, how much balance do you shoot for? It seems like most production model engines are pretty light on counter balance, but don't seem to suffer much.

Greg
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on December 28, 2014, 02:29:21 PM
Greg,

It is impossible to balance a single cylinder reciprocating engine's forces. However, a partial balance can help greatly in reducing second order forces in a single cylinder engine. Some miniature engine builders have been able to use Ricardo's formula for balancing single cylinder engines. 1/2 the total reciprocating weight, which is the piston, wrist pin, "C" clips, upper end roller assembly if used & the upper half of the connecting rod, plus the total rotating weight, which is the bottom half of the connecting rod & any lower end roller assembly, should be on the crankshaft's counter balance. This works on engines that have a "hanger type piston", similar to that shown in the photo, because there are no piston bosses & a very short wrist pin. Some engines with hanger type pistons also had windows in the piston's circumference which further reduced the reciprocating weight. Many of these engines used a single ring or a Dykes type ring with chromed bores & steel roller type connecting rods.

In my engines, the piston bosses, long wrist pin length, steel "I" beam connecting rod, & the bottom end roller assembly make the use of Ricardo's formula impossible. The counter balance weight becomes much to heavy for very high engine RPM's (26,000 to 35,000) & will cause severe vibration. Through trial & error, I found that 33 to 35% of the total reciprocating weight, plus the total rotating weight, will make the engine run smoothly in it's operating range, 12,000 to 32,000 RPM.

It should be noted that a heavier crankshaft counterbalance does increase the crankshafts overall inertia & this will make the engine run smoother in the high rev range because there will be a decrease in the engine's cyclic speed variation. The cyclic speed variation which is reduced by the greater inertia, gives more effective time area numbers at high RPM's. This is clearly demonstrated in several SAE papers on the subject & dynamometer tests.

This explains in part why production model engines are using light weight counter balances. They also have a problem with their short connecting rod center distances. The connecting rods in my engines contain no bushings & no roller assemblies in the upper ends, which allows the connecting rod to be lengthened to it's maximum length. A 2 to 1 ratio; the connecting rod's center distance compared to the engine's stroke is considered optimum. My connecting rod itself may be heavier, but the reciprocating weight is much lower ( smaller piston bosses) & the piston slapping is reduced to a minimum.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Roger B on December 28, 2014, 05:47:46 PM
As always thank you for posting all this knowledge and experience on here. Much is outside my current experience but there is a lot here to learn  :ThumbsUp:  :ThumbsUp:
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: dieselpilot on December 28, 2014, 11:16:56 PM
Thank you for your reply. I understand the fundamentals of balance, I was just looking for some empirical data so that certainly helps. Based on some CAD models of RC engines, I found a few to be about 20-25%. Balance comes in different flavors for single cylinders and some of the resulting feel depends on engine mounting orientation and rigidity, and also the ratio of the imbalance forces vs the mass of the entire engine. As you say, less reciprocating mass always wins.

Greg
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on December 29, 2014, 01:28:57 AM
Greg,

Rigidity is very important, especially for engines with cantilevered type crankshafts. If you were to put a strobe on the front end of an engine turning 30,000 RPM, you would be surprised at the large amount of movement, in a circular path, that is taking place, even with the engine bolted down to a very solid metal mount. Some engines, such as the Nelson FAI speed engine,  have an additional set of mounts on the front end to prevent this movement. I use a hardened steel front end & a machined crankcase on my engines to eliminate this unwanted movement. The photos shows the 6 mounting bolts used on the Nelson FAI engine. The engine also uses a balanced flywheel to counter balance the very large induction window in the crankshaft.

JA
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Niels Abildgaard on December 29, 2014, 06:37:43 AM
Hello Jim Allen

Thank You for a most fantastic thread with explanations and pictures.
I am a little obsessed with replacing all vibrating single cylinder two strokes with 90 degree ,common crankcase twins.
Is there anything in the racing rules, You obey ,that makes this illegal?
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on December 29, 2014, 01:58:38 PM
Niels,

Engine classes are determined by displacement,  not by the number of cylinders, either common crankcase or geared. A 90 degree, common crankcase twin could be made to run with very little vibration. I think another consideration would be the wide width of such an engine.

JA
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Niels Abildgaard on December 29, 2014, 03:18:19 PM
Jim

The interesting thing here is mass.The flywheel and crank can be half mass  of a single.Port areas are up,piston speed less for same rpm if geometry ,ie bore/stroke ratio is the same and the charge air pumping is done by two resonant exhausts instead of one.To See if this kind of reason is valid it could be fun to scheme one as competitor to the configuration You have now,being State of art I would say.
Have You ever considered releasing drawings to us two stroke lovers?
The real stumbling block is to make a non overhung crankshaft that stands rpm on the far side of 500 rpm and still allowing this enormous flow of air and fuel.I will try to reread the whole thread and see how much dimensions You have given already.
It has been a wonderfull mental journey until now.
A happy new Year to You and all Your admireres.
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on December 29, 2014, 03:45:59 PM
Hi Jim. Sorry for the dumb question. I read through the entire post a few times & still at a loss to visualize your method to finish the chromed liner. You mentioned a few points that caught my eye & attached (what I think) to be a fixture related to the operation. But how exactly is it used? 'Grinding' (to me) conjures an image of a powered rotating abrasive tool brought against the part. Is there a motorized aspect to this? What does the business end of the grinding tool look like? How do you preserve the pre-chromed taper angle during finishing? Thanks in advance! -Peter

(reply 3)
- No lapping compounds of any kind, including non-embedding types, should ever be used to fit a piston in ABC or AAC engines
- Cylinders are machined with their taper amount & then chrome plated with approximately .0015" thick chrome/ side
- The cylinders are then ID ground
(reply 35)
- Cylinders in nitro engines such as the Nelson are honed on a Sunnen honing machine to give a fine finish in a short amount of time.
- Cylinders in my .90 cu in engine are ground & will have an even better finish than honing

Peter,

To begin, I will describe a method used to set the compound accurately & quickly without the use of gauge blocks & a sine bar. The "taper masters" shown in the photos are machined with a length that is at least 2X the actual length required, but sometimes 20X the actual length required. Each, marked for location, "taper master" can be reset while being held in a precision grade collet & indicated at both ends for concentricity. A .00005" indicator is used for this operation & the setting of the compound's angle. A Themac tool post grinder, turning at 26,000 RPM, is mounted to the compound to grind the cylinder's ID taper. The grinders stone is diamond dressed after mounting.  The fixture, mounted in a collet,  allows for precise centering of the cylinder by indicating the cylinder's OD.

The photos show the same procedure which in this case is done for precision split collets used to clamp a cable drive to the engine's flywheel. The compound is set with a "taper master" as described in the procedure above. Again the stone is dressed after mounting the tool post grinder. Since the ID of the collet is much smaller then the ID of the cylinder, the grinding stone's RPM is raised to 40,000. I prefer to use a Themac tool post grinder because it is the only tool post grinder that allows precise centering of the grinding stone's center, with its unique rotating mounting of the spindle.

Grinding gives a superior finish to the chrome that cannot be achieved with honing, even if the cylinder is finished honed with 95 grit stones.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on December 29, 2014, 04:02:45 PM
Jim

The interesting thing here is mass.The flywheel and crank can be half mass  of a single.Port areas are up,piston speed less for same rpm if geometry ,ie bore/stroke ratio is the same and the charge air pumping is done by two resonant exhausts instead of one.To See if this kind of reason is valid it could be fun to scheme one as competitor to the configuration You have now,being State of art I would say.
Have You ever considered releasing drawings to us two stroke lovers?
The real stumbling block is to make a non overhung crankshaft that stands rpm on the far side of 500 rpm and still allowing this enormous flow of air and fuel.I will try to reread the whole thread and see how much dimensions You have given already.
It has been a wonderfull mental journey until now.
A happy new Year to You and all Your admireres.

Thank you Niels, but you would be appalled at the quality of the prints, sketches or drawings used to make this stuff. I have always been able to machine parts with a visual idea, some key dimensions, & drawings made on .100" grid graph paper. Many times I draw things at a ratio of 1 to 20 & take measurements directly from from the drawing with a machinist scale. No Solid Works, Auto Cad or Pro-E used or CNC equipment ever used. Most of the tools & machines I use would not be familiar to present day machinist.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on December 29, 2014, 04:26:40 PM
Here are more examples of "taper masters". The pieces at the bottom are used to cut taper amounts that vary by .001" over a distance of .100" on pistons. The piston's circumference at it's top is tapered for use in tapered cylinders. The pieces are machined 20X longer in length to make setting of the compound accurate. For a .001" taper per side, the diameter at both ends vary by .020" over a distance of 2.000". The top pieces in the photo are used to cut or grind tapers in cylinders. They are 2X the actual length of the 1.635" length needed. The diameters at both ends vary by .001" but over a distance of 3.270".

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: petertha on December 29, 2014, 07:31:59 PM
- A Themac tool post grinder, turning at 20,000 RPM, is mounted to the compound to grind the cylinder's ID taper.
- Since the ID of the collet is much smaller then the ID of the cylinder, the grinding stone's RPM is raised to 40,000. I prefer to use a Themac tool post grinder because it is the only tool post grinder that allows precise centering of the grinding stone's center, with its unique rotating mounting of the spindle.
Jim Allen

Fascinating. Thanks again. You just answered my next question about tool post grinder. I guess its safe to say a jerry rigged die grinder would have insufficient accuracy, bearing/runout etc. attempting this level work? Would you mind telling me your model number or recommendation for ~14" swing lathe. I'm guessing they are $$, but always had a dream to maybe dual purpose the unit in a self made 'tool grinder' type machine.

Re the rotary stone, what sort of abrasive type & grit progression do you recommend on chrome?

Can you re-dress the stone mid-way a surfacing operation & somehow maintain the reference ID datum? Or you mean once set up, its put to work until completion of the grinding job?

Do you prescribe a typical criss-cross hatching pattern after the grinding with separate tooling/procedure or is there some trick to replicating with the Thermac & lathe compound motion?
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: dieselpilot on December 29, 2014, 08:30:48 PM
Jim, don't you grind on a "real" cylindrical grinder? On the lathe, I'm going to assume you're using a taper attachment, and not feeding with the compound? Setting the compound at oh 5.74 to get .0002" on diameter with .001" feed on the compound? I can't ever imagine feeding my old Clausing with the compound for grinding, or that Super 11 is a very nice lathe.

Greg
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on December 29, 2014, 10:21:54 PM
- A Themac tool post grinder, turning at 20,000 RPM, is mounted to the compound to grind the cylinder's ID taper.
- Since the ID of the collet is much smaller then the ID of the cylinder, the grinding stone's RPM is raised to 40,000. I prefer to use a Themac tool post grinder because it is the only tool post grinder that allows precise centering of the grinding stone's center, with its unique rotating mounting of the spindle.
Jim Allen

Fascinating. Thanks again. You just answered my next question about tool post grinder. I guess its safe to say a jerry rigged die grinder would have insufficient accuracy, bearing/runout etc. attempting this level work? Would you mind telling me your model number or recommendation for ~14" swing lathe. I'm guessing they are $$, but always had a dream to maybe dual purpose the unit in a self made 'tool grinder' type machine.

Re the rotary stone, what sort of abrasive type & grit progression do you recommend on chrome?

Can you re-dress the stone mid-way a surfacing operation & somehow maintain the reference ID datum? Or you mean once set up, its put to work until completion of the grinding job?

Do you prescribe a typical criss-cross hatching pattern after the grinding with separate tooling/procedure or is there some trick to replicating with the Thermac & lathe compound motion?

My tool post grinder is a Model J-45 with a 2025 spindle. It is intended for 12" to 14" swing lathes. All the tools in my shop have been modified to give better performance. The grinder has a custom, hardened & ground base, that allows it to face grind or circumference grind pieces. The diamond dresser can be mounted to the lathes bed or in the lathes spindle. The 2025 spindle bearings have been replaced with Barden ABEC 7 bearings which are preloaded. I use a special permanent grease to prevent the spindle bearings from overheating. The grease is the same type that would be used in any quality surface grinder which has a permantely lubricated Pope type spindle..  I make the stones, which are mounted on tapered mandrels of different lengths, from scrape surface grinding wheels. For example, the ID of the engine's cylinder is 1.125". I drill a 1/4" hole & cut with a band saw, 1/2" or 3/4" wide, 100 grit aluminum oxide wheels which are dressed round after mounting. The size of the dressed wheels are approximately 1.000" to 1.100". I use a sulfur based grinding oil, Sunnen #MB 30-5, which has been used to previously grind chrome. In the photo notice that the lathes bed is completely covered. The oil is caught in a basin below the lathe's bed to be used again & again & again. Never use new grinding oil to finish grind hard industrial chrome. No dressing of the stone will be necessary to finish many pieces. The typical amount of chrome to be removed will be less than .0005" per side. To make all the cylinders being ground a particular size, a tapered hardened steel gauge is used to measure the ID. It's depth in the cylinder determines what size is being ground. Notice the .00005" waterproof, jeweled movement, indicators that tell exactly where the carriage, cross slide or compound are & how far they are being moved.

No cross hatch pattern is used in an ABC or an AAC type engine because there is no piston ring to be seated. ABC means an aluminum crankcase with a brass cylinder that is chrome plated. AAC means an
aluminum crankcase with an aluminum cylinder that is chrome plated. In ringed engines the cross hatch pattern is important not only for helping to seat the piston ring, it also determines how the piston ring is going to react as the piston moves up & down. If the pattern is to flat, it can cause the piston ring to flutter as the piston moves up & down. If the pattern is to steep, it can cause the ring to want to rotate as the piston moves up & down.

Note: I use the Themac tool post grinder with a custom mount on my Super Tech OD, ID grinder. The reason is, the grinding of small ID holes must be done at very high spindle speeds. Is there an ID grinding attachment for an OD, ID grinder which can rotate at 42,000 RPM?

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on December 29, 2014, 10:40:46 PM
Jim, don't you grind on a "real" cylindrical grinder? On the lathe, I'm going to assume you're using a taper attachment, and not feeding with the compound? Setting the compound at oh 5.74 to get .0002" on diameter with .001" feed on the compound? I can't ever imagine feeding my old Clausing with the compound for grinding, or that Super 11 is a very nice lathe.

Greg

Greg,

No taper attachment that I know of would be able to grind a precise taper in the cylinders ID if you're using a lathe for this job. All of the cylinders shown in the posted photos were ground using the Super 11 lathes compound. However the compound & the cross slides ways were ground to give a very smooth movement. Setting of the compounds angle is done with the "taper masters" as previously explained. The .00005" indicators mounted on the carriage, cross slide & the compound tell me where these thing are & if they have moved from where they were set. I learned a long time ago that INDICATORS DO NOT LIE.

As a matter of fact I have done OD, ID grinding on a 13" Clausing Glochester tool room lathe & a 14" G4002, Chinese iron, Grizzly lathe with the same Themac tool post grinder shown.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: dieselpilot on December 30, 2014, 01:26:48 AM
OK. I didn't think such precision grinding was possible with the compound. I don't know if my lathe would be capable, but I'll give it a try as soon as I get my Dumore reassembled. Fortunately, most of my grinding needs will be straight.
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on December 30, 2014, 02:09:14 AM
Here's another photo of a cylinder that just came off the lathe. Before you begin, use an indicator to see how much play there is in the gibs as you move the cross slide & the compound. Apply some force with your hand as you move each part. Any looseness will allow the vibrations from the grinder to be transmitted to the compound, to the cross slide & then to the carriage. Bad bearings in the spindle or motor cannot be tolerated. The flat belts used on the pulleys & the pulleys themselves must be in good shape. When the grinder is mounted & running, a .00005" indicator's needle will be stationary if there are no vibration problems. If the indicator needle in dancing, it will be impossible to grind to a specific dimension.

Hope this works for you. Making sure that everything is absolutely rigid is one key as well as the mechanical correctness of the grinder.

JA
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on December 31, 2014, 01:09:50 PM
Jim, don't you grind on a "real" cylindrical grinder? On the lathe, I'm going to assume you're using a taper attachment, and not feeding with the compound? Setting the compound at oh 5.74 to get .0002" on diameter with .001" feed on the compound? I can't ever imagine feeding my old Clausing with the compound for grinding, or that Super 11 is a very nice lathe.

Greg

Greg,

I do have a "real" cylindrical OD, ID grinder. I find it is easier & quicker to set up the lathe's compound for small ID, short length pieces where small quantities are needed . I have a highly modified taper attachment which remains permanently mounted that is primarily used for machining tapered tuned pipe sections. The lathes custom cooling system is made of fully adjustable stainless steel pipes & uses only Mobilmet Omicron cutting oil; never any type of water soluble coolant. The four way hardened & ground tool holder is also custom made & it can be easily moved to the taper attachment. A special custom designed high pressure lubricating gun uses way lube to lubricate the carriage, cross feed & compound ways. Notice the additional custom made felt way wipes added to the carriage, the cross feed & the taper attachment ways to keep dirt out.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Roger B on January 06, 2015, 08:23:47 PM
Thank you once again for the incredible amount of information you are posting  :praise2: One of my next projects will require some fine grinding and you have given me a good number of hints and tips  :ThumbsUp:
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: petertha on January 08, 2015, 02:21:33 AM
OK. I didn't think such precision grinding was possible with the compound. I don't know if my lathe would be capable, but I'll give it a try as soon as I get my Dumore reassembled. Fortunately, most of my grinding needs will be straight.
I was going to ask a similar question but will pose in a different way. I always assumed the compound would be set to some nominal, shallow angle so a small incremental feed would translate into a teeny-er amount of stock removal at the grinder wheel. For example, if compound angle = 15 deg, Sin(15)=0.259, so a 0.001" compound dial feed = 0.000259"on the work piece? Is that the concept?

But maybe we are talking about another issue in terms of the whole carriage movement against the lathe bed, or in this case, an angle/taper following type attachment?


> I drill a 1/4" hole & cut with a band saw, 1/2" or 3/4" wide, 100 grit aluminum oxide wheels which are dressed round after mounting

What kinds of tools are required to make holes in AO wheels like this? Do you then bond in a steel axle/mandrel before the final shaping & dressing? I had no idea this was custom wheel making even possible.
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on January 08, 2015, 02:58:30 PM
OK. I didn't think such precision grinding was possible with the compound. I don't know if my lathe would be capable, but I'll give it a try as soon as I get my Dumore reassembled. Fortunately, most of my grinding needs will be straight.
I was going to ask a similar question but will pose in a different way. I always assumed the compound would be set to some nominal, shallow angle so a small incremental feed would translate into a teeny-er amount of stock removal at the grinder wheel. For example, if compound angle = 15 deg, Sin(15)=0.259, so a 0.001" compound dial feed = 0.000259"on the work piece? Is that the concept?

But maybe we are talking about another issue in terms of the whole carriage movement against the lathe bed, or in this case, an angle/taper following type attachment?


> I drill a 1/4" hole & cut with a band saw, 1/2" or 3/4" wide, 100 grit aluminum oxide wheels which are dressed round after mounting

What kinds of tools are required to make holes in AO wheels like this? Do you then bond in a steel axle/mandrel before the final shaping & dressing? I had no idea this was custom wheel making even possible.

I think we are confusing each other with two different processes. If you are going to grind a straight shaft of any length, it should be mounted between two dead centers. Using two dead centers can only be done in the OD,ID, cylindrical grinder. However, when using the lathe, it can have one dead center which would be mounted in the lathe's tail stock. Before grinding any shaft in the lathe, that needs to have the same diameter on both ends, will require the tail stock's axis to be centered on the spindle's axis. This also applies to machining long straight shafts, which are not tapered. In fact, once I have centered the tail stock's axis to the spindle's axis, I NEVER MOVE THE TAIL STOCK TO CUT ANYTHING TAPERED! I use the taper attachment or the compound. The reason I do this is because sometimes I want to use 00 center drills mounted in the tail stock's drill chuck. Any tail stock misalignment will immediately break very small center drills & drills, especially when they are made of carbide.

A sample shaft, mounted between centers, makes it possible, once the dimension is the same on both ends, to center the tail stock's center to the lathe spindle's center. Once the tail stock is adjusted it should not be moved, even if the lathe's tail stock is ridding on a "V" way. The same process is done in the OD,ID grinder by adjusting the table's angle to give an equal dimension on both ends of the sample shaft. Carbide tipped centers cost more but last much longer than high speed steel centers. A quality high pressure lubricant such as CMD extreme pressure lube #3 should always be used with the dead centers.

No special tools are required to make small size grinding wheels. Any high speed steel drill will make many holes in any type of aluminum oxide wheel. Regrind the cutting flutes when they become to dull. Of course the drill will eventually become garbage. The wheels are rough cut using a course tooth band saw blade. Again, many pieces can be cut & the band saw blade will become garbage. You can make or purchase heavy paper pieces to glue, with rubber cement, on to both sides of the wheels. Clamp the stones to the mandrels shaft with machined steel washers, but never directly on the stone's surface!

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on January 10, 2015, 02:25:29 PM
I would like to share continuing developments concerning the building of very high speed bottom end roller assemblies that would be used in miniature very high performance two cycle engines. Retainers of this design type have been successfully used in engine's operating in the 30,000+ RPM range.

The precision machined retainers shown in the photos are the result of in depth designing & testing. The unique mechanical design (two rollers in each window instead of one) gives a retainer which has a very high load carrying ability, with no loss of limiting RPM, compared to a stock retainer. This happens because the two roller window design increases the standard roller count of 10 rollers, for the retainer's size pictured, to 16 rollers. There is no problem with rubbing friction even though two rollers in each window are in direct line contact with each other. Heat that is normally associated with roller assemblies is a result of the friction caused by roller skewing & roller skidding. The precision machined roller cages shown in the photos totally eliminate roller skewing because the rollers are guided along their center lines from end to end. This type of roller guidance is not possible with any type of snap in type roller cage design! Roller skidding is also greatly reduced because the retainer has very low mass & therefore very low inertia. The metallurgy used is a martensitic, precipitation aging, cobalt strengthened, 18% nickel maraging steel. With a simple heat treatment of 900* F for 6 hours, the C-350 maraging steel reaches an ultimate tensile of 350,000 psi at Rc 60. Some of the special characteristics of this steel would be it's high toughness, ductility, impact, compressive (388,000 psi) & fatigue strengths. The steel is resistance to crack propagation, is easily machined, has minimal distortion, predictable shrinkage & is free of decarburization during heat treatment.

Typical applications for maraging steels which began to appear in the 1960's are guided missile & rocket motor cases, wind tunnel models, recoil springs, landing gear components, high performance shafting, gears & fasteners. Prototype retainers are machined with the modified Brown & Sharpe #1 dividing head shown in the last photos. Fixtures, similar to the type shown, are directly mounted to the Brown & Sharpe's #5 taper dead center. The tapered dead center has been modified with a draw bar & is concentric within .0002".

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Niels Abildgaard on January 10, 2015, 04:42:14 PM
Hello Jim
It is a pleasure to be on Your guided tour
Do You use some kind of protective atmosphere during heating the maraging steel?
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on January 10, 2015, 04:57:52 PM
Hello Jim
It is a pleasure to be on Your guided tour
Do You use some kind of protective atmosphere during heating the maraging steel?

No Niels. Any heat treating furnace that can hold the temperature, 900* F, + or - 5* F  for 6 hours will work. If the alloy was heat treated at this temperature for 20 hours it's tensile strength would approach 360,000 psi. The 6 hour treatment gives 320,000 psi at 400* F. & 300,000 psi at 700* F. After heat treating cool in air to room temperature.

The pie shaped material left in between each double roller window, at the center line of the rollers, is only .027" thick. Notice on the partial print that the pie shaped piece must become thinner as it moves towards the center & wider as it moves towards the retainer's OD.  It remains straight without distortion during heat treating. The retainers are always guided in the connecting rod's ID, never on the crank pins OD.

JA
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on January 11, 2015, 01:40:59 AM
This photo gives a better idea of what the double roller assembly looks like before placing the connecting rod in position. There is approximately .001" to .002" total clearance in each window between the rollers & the cage.

JA
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on February 13, 2015, 02:25:19 PM
Initial testing of the machined double roller retainer design has been successful thus far. The photos show the actual assembly still in the engine after several test runs at very high RPM's (19,000+).

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: /// on February 14, 2015, 02:34:28 AM
Have just read the thread from beginning to end, absolutely amazing work Jim, and thanks for openly sharing such a wealth of knowledge!
I hope to be able to use your chrome plating guidance in future, assuming I can find a source for the various acids required. They are not so easy to obtain in the 'Nanny states' of Australia.
Many thanks.
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Niels Abildgaard on February 14, 2015, 06:07:15 AM
Hello Jim

I thougth You were using Cantilevered cranks only but the last three pictures is a normal pressed up construction?
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on February 14, 2015, 02:24:14 PM
Hello Niels,

I have used both types of crankshafts in engines with different type induction systems. I have also used crankshafts with the induction passage machined in the crankshaft itself. There is an indication in smaller size engines that a cantilevered type crankshaft can produce more HP than an induction system (rotary valve, inverted & standard drum valves, bell valve) which would be driven by the crankshaft. The previous photos show an engine which uses piston porting for the induction process. This is the simplest induction system that can be used but it does not allow independent control of the induction's opening & closing events. The induction timing, which is controlled by the bottom of the pistons skirt, is symmetrical, with the opening & closing the same.

JA
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Niels Abildgaard on February 14, 2015, 03:01:25 PM
Hello Jim.

This corresponds quite well with one of the brains behind the last 125 ccm engine (Frits is his firtst name)

http://www.pit-lane.biz/t5121p680-gp125-all-that-you-wanted-to-know-on-aprilia-rsa-125-and-more-by-mr-jan-thiel-and-mr-frits-overmars-part-4

Somewhere in the very long thread he says that the ideal engine has a funny arrangement  for inlet control like bell,disc,piston port etc for starting and low load ,but when the going gets rough, a permanent open hole is best.You will have to register to see the pictures but the very friendly administrator speaks english and the two Aprilia gentlemen only write in english.
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on February 14, 2015, 03:05:35 PM
I should apologize for skipping over many of the details of exactly how some of these pieces were made. In many instances there are no photos or prints, only the completed pieces & the fixtures used. Three piece crankshafts are machined .005" over size for OD's & .005" undersized for ID's. Grinding of OD's & ID' is done with fixtures such as shown in the photos. Assembly of the three piece crankshafts is done in a die set type fixture & then trued within .0002" in two axes from end to end, with each axis 180 degrees apart. The final truing is done with a four jaw independent chuck & .00005" indication. The crankshaft is zeroed in the chuck at is short end first before twisting & bending the end sticking out. A large, very rigid lathe spindle & a quality independent four jaw chuck make this possible.  I use this level of precision for three piece crankshafts because the engines where they are used have four main bearings, two on each side.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on February 14, 2015, 03:15:57 PM
Hello Jim.

This corresponds quite well with one of the brains behind the last 125 ccm engine (Frits is his firtst name)

http://www.pit-lane.biz/t5121p680-gp125-all-that-you-wanted-to-know-on-aprilia-rsa-125-and-more-by-mr-jan-thiel-and-mr-frits-overmars-part-4

Somewhere in the very long thread he says that the ideal engine has a funny arrangement  for inlet control like bell,disc,piston port etc for starting and low load ,but when the going gets rough, a permanent open hole is best.You will have to register to see the pictures but the very friendly administrator speaks english and the two Aprilia gentlemen only write in english.


I believe you are referring to Frits Overmars & Jan Thiel who are members of The Two Stroke Tech site. Both of these individuals, as well as individuals such as Darcy Rosenthaler, Lohring Miller & others have been invaluable in providing factual, in depth knowledge concerning every aspect of a high performance two cycle engine. There is an in depth discussion about the 24-7 engine theory on this site. I consider the site to be number one in the field of high performance engine building & tuning.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: lohring on February 14, 2015, 04:44:03 PM
Jim, I think it's more that I've learned from you than you from me.  I mostly have off the wall ideas.  You put them into practice.  I'm glad you are finally addressing the connecting rod big end bearing problem in racing gas engines.  That's been a weak link since we were pushing Quickdraws to their rpm limit.  Even modified Zenoahs are seeing rod bearing failures as they run more and more over 20,000 rpm.  My only gas engine rod failure was a bearing cage failure.  This allowed the rollers to skew and the result is below.  Fortunately, the cylinder, an M&D cast unit, wasn't destroyed.

Lohring Miller
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on February 14, 2015, 04:59:59 PM
Lohring,

The person who manufactures the OD engine has purchased some of the latest design retainers to test in his R/C gas cars & on his dyno. He wants to build OD top end assemblies (32 or maybe 34 cc) that could be used on Zenoah bottom ends. Of course the present Zenoah 32 cc bottom ends are failing with 20 ounces of oil/ gallon & engine RPM's of 16,000. This person is not aware of the necessary metallurgy or radial tolerances necessary to give a reliable bottom end assembly that can withstand 24,000+ RPM.

Jim Allen

note: I haven't forgotten about the mold, just cannot find enough time because of what is taking place at Aero Precision Machine concerning the greatly increased Nelson Q-40 production.
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: lohring on February 15, 2015, 06:48:45 PM
We ran into two big end bearing/crankshaft problems in our testing.  Since we were going for straight line speed with existing propellers, top speed was directly related to rpm.  We could run Quickdraws to at least 25,000 rpm for a short time without failure.  They probably developed around 3 to 4 hp at this rpm.  They had a 28 mm stroke and 34 mm bore.  After they noticed big end bluing on their dyno, Quickdraw modified the rod bearing with oil slots and increased clearance.  We didn't experience any problems after that.  My engine, pictured in my last post, had several racing seasons of high rpm operation before failure.  The crankshaft and connecting rod was the stock Zenoah one, the same as Quickdraw used.

On the CMB, a 35 mm bore and stroke engine, we had issues with the crankshaft flexing as shown by flywheel strikes.  The solution was to add another bearing on the front of the crankshaft.  Other problems limited the rpm to around 23,000.   We never had a rod bearing issue so we didn't make any modifications or measurements.  I think crankshaft rigidity is as much of an issue as bearing design, though.

Lohring Miller
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on February 15, 2015, 07:13:17 PM
I totally agree Lohring. There is only one way to prevent crankshaft flexing. Make the crankshaft larger in diameter, mine are 15 mm compared to the stock 12 mm size & make the dog bone a full disk type. Total elimination of roller skewing & limiting roller sliding to a minimum are the other things that would allow the engine's RPM to easily exceed 23,000 & very possibly go as high as 28,000. Increasing radial clearance amounts in roller type assemblies always encourages an increase in roller sliding. Roller sliding is also effected by roller OD finish & the crank pin's OD finish.

JA

note: Lohring, I have been informed that there should be some very encouraging information posted on JRCBD this evening after more wide open throttle testing. More than four 500 ml bags of fuel & no signs of any failures. This is just with a change of the retainers design & all other parts remaining stock including the radial clearance numbers.



Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on March 09, 2015, 10:47:14 PM
For the last month I have continued to investigate the possibilities of bottom end roller assemblies that would be used in 15 to 30 cc two cycle engines. These assemblies must be able to operate in the 22,000 to 28,000 RPM range, at 7.5 to 9.5 HP, with absolute mechanical reliability.

The tools shown in the first photo, as well as the holding fixture mounted onto the Brown & Sharp's solid tapered center, are required to machine the 14 slots in the retainers .5470" OD. The slots are 25.714* apart. A calculation is made of the width of the retainer's pie shaped piece between each .0787" wide slot, measured at the roller's center line. This dimension is approximately .027". The following calculation is made to determine which dividing plate is needed to give 14 divisions of 360*. Since the dividing head is geared 40 to 1, 40 is divided by 14 which equals 2 12/14 = 2 6/7 = 2 42/49. This means that for the indexing of 14 slots, each 25.714* apart, the dividing head is rotated 2 turns (18*) plus 42 holes (7.714*) on a 49 hole plate. The dividing head is rotated an additional 2 holes to give .001"+ clearance (.0797") for each roller in it's slot. Again the 40 to 1 gear ratio means that one complete rotation must equal 9*. Using a 49 hole plate means that each hole equals 9* divided by 49 or .1836* (11 minutes). Therefore, two holes on the 49 hole plate equals .3672* (22 minutes). This is sufficient to give the necessary .001"+ clearance in each slot.

The dividing head repeats accurately because there is no vernier scale to read. The spring loaded tapered pin must drop in it's hole for indexing amounts. The two photos before the last two show how easy it is to index & open the slot for the .001"+ clearance.

The last two photos show how the machined sleeve is mounted & located precisely for machining. By using a solid aluminum mandrel inside, which is located in the holding fixture, there are no burrs to be removed on the ID of the retainer after machining. Tumbling removes any burrs on the retainer's OD. The sample roller & the gauge pin act as go-no go gauges for slot measurements.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: 90LX_Notch on March 10, 2015, 12:11:10 AM
Jim-

I've been following this thread from the beginning.  The "full on" effort is beyond words.  High end competition is always about the details and your attention to details is amazing.  Thank you for the education and your willingness to share with us.

-Bob
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on April 05, 2015, 06:12:46 PM
It should be noted that the building of very high RPM, high HP, connecting rods "CANNOT" be made to operate mechanically reliable without consideration of wrist pin, crank pin & crankshaft axis squareness. Keeping these axes square to each other can become difficult if not impossible without proper machining fixtures & jigs. Squareness of + or - .0002"/ 6" allows connecting rods to be built with .0001" radial clearance in the top end & .0003" radial clearance in the bottom end over a connecting rod center distance of 1.741".

The crankcases in the first photo are machined from aluminum alloys 2024 T-351 & 7075 T-651. Several crankcases were machined from 12 L 14 Leadloy steel & these were used for dyno testing only. Transfers are broached machined from the inside of the cylinder bores using a proprietary process. Different transfer shapes: number of transfers; entry angles, both axial & radial; as well as different depths were dyno tested. After many hours of testing, I can only say, without any doubt, that bigger area transfers DO NOT necessarily mean more HP. However, a steel crankcase runs faster than aluminum because of the greater rigidity of steel.

The bottom & rear of the fixture shown is square within .0001" over 6". When mounted to the machined face plate of the lathe, the cylinder bore & the front end bores can be machined square to one another. The face plate is mounted to the lathe's spindle with a D-4 camlock nose. Two .3752" dowel pin locations in the bottom & the rear of the fixture make precise re-location easy. The fixture is held securely to the lathe face plate with a custom made draw bar extension. Cylinder liner bores & crankshaft bores THAT ARE NOT SQUARE TO ONE ANOTHER produce all types of unsolvable mechanical problems, such as, connecting rod walking on the crank pin; cocking of the piston in it's bores; poor wear characteristics in bushed & roller type rods; high wear in piston boss holes; high friction & heat in associated parts; etc.

The four small diameter locating pins located on the top of the fixture, beneath the clamping devices, engage the four crankcase mounting holes with a tight fit. The engine begins as a block of metal with the mounting lugs already machined. It is clamped for all machining operations while in the fixture including the cylinder bore & face; the front end bores & face; the back end bore & face; 8-32 threaded holes for the front & back ends; 8-32 threaded holes for the head bolts; the exhaust outlet & the 8-32 threaded holes for the exhaust header; profiling of the crankcase outside & the internal broach cutting of the transfers.

More to come........................

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Admiral_dk on April 05, 2015, 09:32:33 PM
I'm still very impressed and grateful for your explanations - it's nice to see that I'm still able to learn something about two-strokes and more about how to make them  :cartwheel:

Best wishes

Per
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on April 05, 2015, 10:38:26 PM
90LX_Notch & Admiral_dk,

Building mechanically reliable, very high RPM, very high HP, two cycle engines has very little to do with what most people are trying to do to these things. The ability to machine designed tolerances to exacting numbers always tells the designing engineer which number is working & which number is not working. NUMBERS, NUMBERS & more NUMBERS applied to such things as axial, radial, roundness, squareness, tensile, yield, ductility, metallurgy, etc., etc., allow the design engineer who is capable of making the "number", to find solutions to problems. I am quite sure you both understand exactly what is being said here.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on May 10, 2015, 07:40:45 PM
I'm in the process of relocating. I haven't had time for the engine building stuff except for the latest connecting rod project. The new rods are a replacement for the failing Zenoah 320 connecting rods. The other  photos are what should not be done & the results of a very poor design.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on May 11, 2015, 08:00:43 PM
The machined connecting rods shown in the photo are a direct replacement for stock connecting rods that fail at sustained RPM's of 16,000. Incorrect design, tolerances, metallurgy & heat treatment can prevent the building of any high performance connecting rod.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: 90LX_Notch on May 12, 2015, 01:24:28 AM
Thanks for the update Jim.  I'm still following along with great interest.

-Bob
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on June 29, 2015, 12:16:50 AM
Heavy heat treating fixtures will be used, with the rods clamped in between, to prevent any bending or twisting of the machined connecting rods during hardening. The rods & their fixtures will be sealed in air tight .002" thick stainless steel bags to prevent any decarburization during the through hardening process. The Sen/Pak System of heat treating utilizes a metal foil container to provide a protective sheath and to automatically neutralize the entrapped atmosphere. The lightweight Sen/Pak container heats more rapidly than the work piece. As a result, the undesirable elements in the entrapped atmosphere react with the Sen/Pak container long before the work piece is hot enough to be damaged by them. In addition, the Sen/Pak container acts as a protective barrier throughout the hardening and quenching operation.

After double tempering the rods will have a 315,000 psi tensile strength & a 210,000 psi yield strength at 58 Rockwell C. They will also have a Charpy impact value of over 224 ft-lbs. These rods will have no bushing or roller assembly in their top ends. They will run with the connecting rod's material directly in contact with the hardened wrist pins used. The upper & lower holes of the connecting rod will be aligned ground to each other in both axes within .0002"/6.000" by using a special designed holding fixture.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Admiral_dk on June 29, 2015, 07:29:04 PM
Again thank you very much for your contribution to the collective knowledge.

It's amazing how much extra work is included in order to reach the last bit of performance combined with reliability. But seeing that you reach 480 HP/L and I just got to 240 HP/L on my 50cc motoX bike in my youth (12 HP and I started with 2.5 HP) makes me realize that I would have been in trouble if I had any competition that had much more power than me. I could probably had reached 14-15 HP before my crankshafts and conrods wouldn't survive the extra power and then I would not be sure I could trust the gearbox either ....
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Roger B on July 02, 2015, 09:36:56 AM
I'm still quietly following and learning  :headscratch: Thank you again for keeping posting  :ThumbsUp:  :ThumbsUp:
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on July 02, 2015, 02:55:18 PM
Thanks much Guys.

Admiral_dk, considering that Denmark is connected to Sweden by a bridge-tunnel, do you by any chance know Swedish tether car racers Nils Bjork, Jan-Erik Falk, Rune Granberg, or Mats Bohlin. Sweden They visited my machine shop in 2005 while competing at the US Tether Car Nationals held on Long Island. Information about the visit, with photos,  was posted on the Swedish Internet, September 7, 2005. These very advanced tether car modelers, some who held world records at that time & some who still hold world records, understand the value of  metallurgy, design mechanical engineering & in depth testing. Another person in the United States, who has done the same type of in depth tether car model engine development, as well as mechanical development of the car itself, would be John Ellis of New Jersey.

I presently work at Aero Precision Machine Inc located in Liberty, North Carolina, USA. The owner, Mike Langlois & I, build at this site, the world famous Nelson Q-40 pylon racing engines sold world wide. The engine's parts are manufactured on the best CNC lathes & mills available, to very tight tolerances (typically .00005"). All assembly & repair of these engines is done on site by myself. We intend to build now & in the future, the finest engine of this type any where in the world. The quality of every aspect of these engines, including Swedish custom bearings made by WIB, crankshafts, crankcases, cylinder machining, cylinder chroming & honing as well as hand fitting is done on site, under very tight controls.

There are no short cuts to be taken when attempting to build very high performance two cycle racing engines!!

Jim Allen



Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on July 02, 2015, 08:58:19 PM
Sen/Pak heat treating bags are shown in the two photos. Oil hardening steels that are sealed in these stainless steel bags will not be decarburized or have their surfaces dulled during heat treatment. It should be noted that oil hardened tool steels will not be hardened properly without the pieces coming in direct contact with the hardening oil. Therefore, holes will be punched in the bags after they are immersed completely in the hardening oil! The hardening oil is also heated 90* F to prevent thermal shock. A minimum of 5 gallons of standard hardening oil will be needed for connecting rods, crankshafts, front ends & induction valves.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on July 09, 2015, 11:02:49 PM
The two connecting rods on the left have been heat treated & double tempered. Notice they have no scale from decarburization, but they do have a darkened color from being double tempered. The bottoms of the hardened & tempered rods were lapped on their outer surfaces to ensure a flat surface for the Rockwell test that was preformed. At the very bottom of each piece you can see the indentation mark from the diamond penetrater used in the hardness test. The rods are 56+ Rc hardness. The next step is to align grind, in two axes, the two holes to each other & have both holes to their finish dimensions.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: petertha on July 11, 2015, 05:52:17 AM
Sen/Pak heat treating bags are shown in the two photos.....Therefore, holes will be punched in the bags after they are immersed completely in the hardening oil!. Jim Allen

Very interesting, Jim
- are the foil bags themselves filled with an inert gas or something consumable to mitigate oxygen inside while being sealed up?
- is the general idea of punching the bag while submerged that oil floods in & contacts the steel (ie not atmosphere/oxygen)
- what does double tempering accomplish & what's the methodology? (ie a repeat of temper #1 or different temp/time recipe?)
- maybe I missed, but interested to know what heat treating oven you use

thx/Peter
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on July 11, 2015, 04:29:24 PM
Sen/Pak heat treating bags are shown in the two photos.....Therefore, holes will be punched in the bags after they are immersed completely in the hardening oil!. Jim Allen

Very interesting, Jim
- are the foil bags themselves filled with an inert gas or something consumable to mitigate oxygen inside while being sealed up?
- is the general idea of punching the bag while submerged that oil floods in & contacts the steel (ie not atmosphere/oxygen)
- what does double tempering accomplish & what's the methodology? (ie a repeat of temper #1 or different temp/time recipe?)
- maybe I missed, but interested to know what heat treating oven you use

thx/Peter

A lot of intelligent questions asked here Peter, which I will try to answer.

There is no inert gas of any kind used inside the sealed, high chromium stainless steel, bags. "The lightweight Sen/Pak container heats more rapidly than the work piece. As a result, the undesirable elements in the entrapped atmosphere react with the Sen/Pak container long before the work piece is hot enough to be damaged by them. In addition, the Sen/Pak container acts as a protective barrier throughout the hardening & quenching operation." A preheating soak of the piece in it's bag at 1350*F to 1375*F is done first. Then the piece is raised to the  hardening austenitizing temperature of 1770*F to 1780*F & allowed to soak again. The entire bag is submerged in heated (90*F) standard hardening oil & holes are immediately punched in, which prevents the heated piece from ever being exposed to the atmosphere. After the piece has cooled to approximately  150*F, I use a double tempering operation at 400*F to bring the piece to it's final temper. At this point the piece is not clamped between the heavy steel pieces. The double tempering operation is only necessary for sections greater than 1.000" thickness. However, I have always, after cooling the piece to room temperature, tempered a second time at the 400*F temperature.

I use a Lucifer heat treating oven, with a digital temperature control, capable of holding the temperature at + or - 5 *F up to 2300*F. I use a Paragon High Fire Kiln with a Staco Energy Variable Auto-Transformer & an Omega HH-99A-K thermo-couple digital thermometer for tempering operations. I can hold  the tempering temper at + or - 2* F with the variable transformer controlling the voltage to the ovens heating elements.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on July 31, 2015, 02:38:41 PM
The photos show some of the processes involved in making a fixture capable of grinding both the upper end & bottom end connecting rod holes parallel to each other in two axes at the same time. During the align grinding process the holes are also made to the correct size within + or - .0001". The connecting rods are through hardened & double tempered to give an ultimate tensile strength of 315,000 psi at 58 Rockwell C. With the custom double roller machined retainers shown they will be tested at 23,000 RPM.

In the upper part of the last photo can be seen the latest machined retainers & rollers to be used with stock Bi-Zeta connecting rods. They have 14 rollers, of the same size, compared to the stock retainer with 9 rollers. They are being tested at RPM's beyond 23,000 on my test stand. The small toe clamps at the bottom of this photo will hold the connecting rods in place after to locating pins are removed to allow through hole grinding.  Notice the use of two clamping screws, a jack screw in the middle & the slotted end of the fixture. After the hardened & ground .750" X .625" locating pin is zeroed (big pin at the bottom of the last photo), it remains in place while only the fixture is moved to automatically locate either hole for grinding. Since all holes are bored without moving the fixture, all holes in the clamped connecting rods ground with the fixture must be square & parallel in two axes at the same time. After final grinding they are square to each other within .0002" over 3.000".

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on August 11, 2015, 01:41:49 AM
I have now completed the holding fixture; it's locating pins for the upper & lower holes; the clamps for the upper & lower connecting rod ends; the hardened & ground mounting arbor, which when zeroed, will accurately  locate the fixture in the same location each time. This means each connecting rod will have the exact same center distance. In addition, each connecting rod ground on the fixture, will have both holes square & parallel to each other in two axes at the same time. I will set up the Themac tool post grinder & use gauge pins to grind the holes to the correct size.

The connecting rod is first located on the, clamped into position, locating pins. Then the rod itself is clamped to the top of the fixture with 4, 6-32 SHCS using the machined circular clamps. Unscrewing the top 10-32 SHCS's at both ends of the fixture & applying a slight amount of pressure with the two 10-32 jack screws in the middle at both ends, releases the locating pins, which now can pass out through the bottom of the fixture. Now the through hole grinding of the connecting rod's holes can be done & the mounting arbor, coming from the bottom of the fixture, can be securely clamped into position with the bottom two 10-32 SHCS's at both ends.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Roger B on August 11, 2015, 07:34:36 AM
Fascinating work  :ThumbsUp:  :ThumbsUp: Still following along with interest  :wine1:
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: KB on August 11, 2015, 04:44:28 PM

"Strictly Business" - the name says it all!

Your dedication to precision craftsmanship and knowledge of metallurgy is amazing.

- A friend of mines business motto; "...where quality is non-negotiable"

Thank you for taking the time to share all that you do.
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on August 13, 2015, 02:46:16 AM
I'm showing something a little different that  I have been working on for some time. Two .8966 or .9467 cu in, custom built engines, are precisely located in the bored mount to give the correct gear mesh. This is made possible with the precision, concentrically ground, OD's & ID's of the full hard AISI O-1 steel front ends which are located in the precision, jig bored, 2024 T-351 aluminum engine mounting blocks. Notice that the engines are securely fastened with 12, 8-32 screws, 6 on each side, tightened to 50 in lbs of torque. The 4, 8-32, FHSS on the top of the engine mount also clamp the center gear housing securely in place.

The gear ratio used is 1 to 1, which means the torque & HP are doubled at the propeller while the engine's RPM remains the same, minus any gear loses. Properly designed spur gears have an efficiency greater than 98%. (Dudley's Gear Handbook; 2nd edition; chapter 12) With each engine developing 7+ HP at 30,000+ RPM & 290+ in ozs of torque, at the propeller, there will be 14 HP at 30,000 RPM & 580 in ozs of torque. The engines are alternate firing & with the wine of the open gears, the setup sounds like a turbine when running.

The gears are made of "certified" unleaded 4340 prehardened (Rc-38) steel. This is the same material used for the gears in John Bridge's highly successful twin engine hydro named the "Led Sled". The gears have been proven to be highly wear resistant & run dry without any lubrication. I machined the gear blanks & the single split tapered sleeves in the same setup. This insured that all the gear internal tapers & all the split sleeve external tapers will match. North Shore Precision Gear & Tool cut nine gears plus two additional sizing gears that are .0002" over & under the nominal size. Only my gear blanks & my tapered sleeves were used to machine these gears with carbide gear hobs. Both engine gears turn in a clockwise direction by using custom made inverted drum valves in the engines, while the propeller shaft rotates counter clockwise, allowing the use of available left hand propellers. There is a substantial weight saving by having one stuffing box, one drive shaft & one strut.

The total weight of the pictured gears with engines is 5 lbs 12 ounces. The main shaft uses a solid 1/4" drive shaft system with ball & pin universals. The universals are a simple form of a constant velocity type universal joint. All the male, female & thrust washer pieces are made from AISI O-1 tool steel. Some pieces are used full hard & other pieces are used as a spring temper. All the technology, metallurgy & engineering used on this set up has been proven to be sound.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Roger B on August 13, 2015, 07:35:14 AM
I see that these engines are watercooled. Do you use a pump for circulation or just scoops facing the direction of travel?
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on August 13, 2015, 12:25:13 PM
Roger,

I use a propeller blast type system with metering plugs at the outlets. Here's a photo of a typical system. Position of the intakes & intake line sizes are important. These things are not dragging in the water; they are approximately 9/16" above the water line a maximum speed.

JA
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Roger B on August 13, 2015, 07:40:14 PM
Thank you  :ThumbsUp:
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on August 16, 2015, 05:25:31 AM
This is how I set up my Themeac, J-45 tool post grinder to finish both holes of the connecting rod. The grinders motor has ABEC 8, permanently greased, sealed, ball bearings & it turns at a load speed of 10,000 RPM. The spindle has the same ball bearings except they are preloaded. The pulleys used will allow the spindle to turn 26,000 RPM. The unique characteristic of the Themac is in it's ability to enable the center of the grinder's spindle to be placed on the center of the lathe's spindle. Notice how the grinding spindle can rotate to any position with it's mounting to the motors OD.

A preliminary check of the hardened steel arbor mounted in the independent 4 jaw chuck shows a dead needle on the .00005" Brown & Sharpe best test indicator. After clamping the fixture with it's mounted connecting rod, another check is made.

The D 1-4 camlock nose on this lathe allows for tooling to be mounted, removed & remounted without the loss of the dead zero. Cleanliness is crucial when using mounts such as this.

The finished surface has an 8 to 12 micro inch finish. A finish which is to smooth of a surface & to much radial clearance will encourage the rollers to slide as they rotate.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Admiral_dk on August 16, 2015, 09:58:25 AM
Thank you again Jim for your explanations  :ThumbsUp:

I must admit that I never thought of grinding the conrod in the lathe like this, but it makes sense - big time  ;D

Best wishes

Per
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on August 16, 2015, 01:34:31 PM
Per,

This method ensures that every connecting rod has exactly the same center distance & both holes will be square to each other in two axes at the same time. Honing can give the correct size, round holes, but it will not correct any misalignment between the two holes. There is always some misalignment with slight distortion due to the machining & final heat treating processes. Very high RPM connecting rods need tight tolerances to prevent roller skewing, roller sliding & high wear. There is no bushing material used in the upper end of these connecting rods. They run with the connecting rod's material directly in contact with the crank pin's material. The radial clearance in the top end is .0001" to .0002". The radial clearance in the bottom end is .0003" to .0005".

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on August 26, 2015, 10:41:45 AM
I have completed the ID grinding of the upper connecting rod holes in our sample pieces. We hope that the time spent selecting a suitable through hardening alloy & the align grinding of both bores, will give us the necessary information to move forward on this project. These connecting rods will be tested with the double roller window retainers, which gives 16 rollers compared to the stock number of 9. The ID grinding operation of the upper end hole is done with a 1/4" diameter, Borazon wheel, which has a 1/8" solid carbide shaft. The grinders spindle is turning at 31,000 RPM. Notice how steady the .00005" indicator is during the grinding operation.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: petertha on September 03, 2015, 05:55:53 AM
Notice how steady the .00005" indicator is during the grinding operation.

Somewhere in this thread I asked a newbie question if you were somehow setting your compound at a very shallow angle in order to increment the grinder in small Y amounts rather than trying to split typical 0.001" dial increments going straight across the bed. This probably didn't make much sense to you & now I think I know why. Looks like you set up a DTI & just watch the needle advance so the compound can stay perpendicular, yes? Sheesh, that setup makes so much sense. And it serves double duty as a vibration meter :)

On an operation like this with hardened material, what is a typical amount of in-feed per grinding pass?
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on September 05, 2015, 02:21:10 PM
Sorry Petertha, but it looks as though I over looked this question. I normally use rigidly mounted, waterproof, shockproof, jeweled movement indicators to tell me exactly where things are positioned when using manual type machines that have vernier scales. I have learned that quality .00005" indicators, "DO NOT LIE" about the position or what is actually happening during a machining process.

The amount of out-feed for grinding an ID is never more than .001", which means an increase of .002" on the ID. Always grind so that the wheel can pass completely through & then traverse in the opposite direction at the same rate. Several spark out passes can be used to give a 6 to 8 micro inch finish on the ground surface when necessary. I use a sulfur based honing fluid for all my ID grinding. There should be very little heat generated during the process even though the wheel's RPM exceeds 26,000.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: RcTintin on October 08, 2015, 01:55:30 AM
Incredible work sir.

Please can you share more pics of your machine tools, jigs etc. Also, what lathe and mill do you use?

Fantastic thread, valuable information in here, thanks.

Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on October 15, 2015, 05:12:27 PM
My shop is being re-organized as a result of purchasing a new house for the third time.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on December 04, 2015, 08:39:22 PM
Incredible work sir.

Please can you share more pics of your machine tools, jigs etc. Also, what lathe and mill do you use?

Fantastic thread, valuable information in here, thanks.

The shop is coming along. All machines are in place & under power. Which particular jigs & fixtures are you interested in? There are hundreds of these things which are used to make the same part over & over again to the same tolerance.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: joncarruthers on December 05, 2015, 09:01:32 AM
Thank you Jim, this is a completely new area for me, fascinating.

Do you find any advantage tuning the carb bell mouth length?
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on December 05, 2015, 05:29:05 PM
Thank you Jim, this is a completely new area for me, fascinating.

Do you find any advantage tuning the carb bell mouth length?

Google, Best Bell-Prof. Blair & Associates. Click on related articles. This pdf. is what I used for the design of my carburetor bell mouths. Also found here; File:(Blair and Cahoon) Design of an intake bellmouth Sept , under file history click on date/time.

JA
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: petertha on December 21, 2015, 07:41:51 PM
Hi Jim, I wanted to inquire about one of your earlier replies. From the pics, I didn't really get the sense you were continuously flooding the part with oil (you mentioned 'basin') or maybe I misunderstood. Is it sufficient to pre-drip some oil in the bore to assist with grinding, or did I miss the detail here? What is significant about previously used oil vs. new oil?  Is there any consideration to the lathe rpm, or basically as long as its moving & correct counter-grinder direction? (ie. higher lathe rpm more/less prone to vibration?). What about X-travel rates, is slower better or just whatever cuts best with a particular grit? I'm amazed at the mirror finish of #100, is that about as fine as you go for chrome?

1/2" or 3/4" wide, 100 grit aluminum oxide wheels which are dressed round after mounting. The size of the dressed wheels are approximately 1.000" to 1.100". I use a sulfur based grinding oil, Sunnen #MB 30-5, which has been used to previously grind chrome. In the photo notice that the lathes bed is completely covered. The oil is caught in a basin below the lathe's bed to be used again & again & again. Never use new grinding oil to finish grind hard industrial chrome.
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on December 22, 2015, 10:27:25 PM
Petertha,

When grinding hard industrial chrome, I'm continuously flooding the part. I catch this sulfur based grinding oil (Sunnen # MB 30-5) in a basin beneath the lathes bed & DO NOT allow it to get into the oil based lathe coolant. I have not tested what will happen when only a small amount of oil is placed in the bore before grinding. Sunnen advised that the oil used to grind chrome should be used again & again. They said the finish would improve with continued reuse. I always rotate the part as slow as possible in a direction which is opposite to the grinder's spindle. Lathe RPM's of 50 to 70 & grinder spindle RPM's of 20,000 to 26,000 work the best on the 1.125" bore. Always use the largest diameter stone possible in a particular bore. Vibration problems can come from bad bearings in the grinder's or lathe's spindle, the grinders motor, a part that is not rigidly mounted or a tool post grinder that is not rigidly mounted. Always feed the X-travel at the slowest rate possible so that no heat will be generated in the part. Always feed completely through the bore before reversing directions. Sometimes after putting on to much chrome a 60 grit wheel is used for roughing. Finish is still done with the 100 grit stone.

This process is similar to what is done on the Sunnen honing machine except the cylinder is held by hand. It is stroked in & out as the single stone mandrel is rotating. Rotational speed is approximately 400 RPM & the stones used are from 280 to 400 grit. The stone in the mandrel is under pressure which is applied with a foot pedal as the mandrel is rotated. The same type honing oil is used & the finish is comparable to the 100 grit ground finish.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: petertha on January 31, 2016, 07:11:42 PM
Hi Jim. I'm looking at some of your lathe bed wheel dressing fixture pictures. Does your work routine go:
- initially dress the wheel with lathe bed fixture in place
- remove dressing fixture altogether, do the part grinding operation
- if grinding wheel requires touch up before part is done, remount the dressing tool & (somehow?) re-register the bore dimensions where you left off
Or maybe I have it wrong & this fixture stays in place during the entire operation? That way you can re-dress at any stage so re-establishes same datum but with a fresh wheel surface so to speak. (Hope my clumsy wording is making sense).

In another pic, you mounted a dressing tool in the chuck. Is this an example of a 'one-type' wheel tune up where maybe you don't have the room to mount the lathe bed dresser?
In this case, do you somehow brake the chuck to prevent the dressing point from rotating (=wheel diameter variation)

-Peter
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on February 01, 2016, 08:06:43 AM
Hi Peter,

The top photo is not a lathe bed. It is the bed of my OD-ID grinder. Look behind the tapered arbor & you can see the OD grinding wheel. I dress either the ID wheel or the OD wheel, remove the dresser & then grind. If the grinding wheel needs to be re-dressed in either case, I remount the dresser. I can easily return to the original position of either wheel because there is a .000050" indicator mounted on the cross feed. The same procedure is done on the lathe shown in the second photo after the spindle is locked.I may have some photos of both machines with their mounted indicators.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: petertha on February 02, 2016, 02:16:28 AM
The top photo is not a lathe bed. It is the bed of my OD-ID grinder. Look behind the tapered arbor & you can see the OD grinding wheel.

Aha, that explains it. I thought maybe it was the Themac installed on a different, prior lathe. And yes, now I see the big OD wheel.
Now I get the L-bracket & your dial indicator setup too. OK, the fog is slowly lifting.
In one of you prior pics you showed a DTI set against the compound & a comment to the effect of nil needle movement during grinding. But now I suspect that wasn't for feed measurement, that was validating 'stability' during running?
(I'll gladly try to absorb any other pics you have, meanwhile thanks for your patience in explaining).
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on February 02, 2016, 04:33:28 AM
Peter,

The Themac is used on both the lathe & the OD-ID grinder. I made a special drop down mount so that I can use it on the OD-ID grinder. The reason for doing this is because the ID grinding attachment that comes with the OD grinder has a low spindle speed. The Themac model J-45 with its flat belts & pulleys can operate from 4200 to 42,000 RPM. The small holes that I grind internally use a spindle speed of 26,000  RPM. I do use the .000050" indicator for precise feed measurement & to tell me exactly where the compound or in-feed position is at all time

Jim
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on February 03, 2016, 11:42:00 AM
Peter,

I will ad to my explanation. I will use several different sizes of no-go, go, gauge pins, when grinding ID holes. I have found this method of measuring to be easier & more accurate than using bore type gauges. For example, a .2500" ID hole is ground in steps starting at .2480". Each gauge pin used will be .0001" smaller than the desired size. Therefore, a .2499" pin will fit snugly into a .2500" hole; a .2479" pin will fit snugly into a .2480" hole. Once you have picked up a size, grinding in steps of the same amount gets the hole to size within + or - .0001". With some practice the process is easy to do.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: petertha on March 03, 2016, 03:43:24 AM
Hi Jim. More ID grinding questions. (I hope you are not sick of me yet  :D).

- when you dress your wheels that are in the smallish diameter range (say sub 1" OD), do you reduce rpm back on the tool post grinder to lowest pulley setup in this mode? ie. something less than what metal grinding mode itself would be? If so, is there an rpm rule of thumb for safety?

- prior to ID grinding, do you set the axis of the grinder spindle at some slight angle relative to axis of work so it cuts with kind of a leading edge effect? Or is the grinder spindle parallel with lathe rotation axis. It was suggested to me that a wider ID wheel and/or parallel running requires some HP on the part of grinder motor. But that Themac model looks pretty beefy.
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: petertha on March 03, 2016, 05:44:01 AM
Hmmm.. going back through the pics maybe I have insight into Q#2 looking at one of your setups if I interpret it correct. You have the tailstock set in the pulley end of the spindle. Assume its zero-zero alignment insurance & maybe helps with vibrations? A lot of details to this grinding business for sure.
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on March 05, 2016, 09:55:21 AM
Hi Peter,

Sorry to take so long to answer. I'm still working on completing the set up of the new shop. I dress the wheels at the speed they will be operated at when grinding. For example, 1/8" to 1/4" wheel diameters are run at 42,000 RPM; 3/8" to 5/8" at 31,000 RPM; 3/4" to 1" at 26,000 RPM; 11/8" to 2" at 9,300 RPM; 21/8" to 4 " at 6,300 RPM; 41/8" to 5" at 4,200 RPM.

I do not set the grinder spindle's axis at an angle to the carriage's axis, because the grinding wheel will be dressed using the carriage's axis. Truing is necessary so that the wheel will be concentric with the spindle's axis. A wheel which is out of round or not concentric will pound the work piece, wear fast & produce poor finishes.

JA
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: petertha on March 05, 2016, 06:58:38 PM
Thanks Jim. Good luck with ongoing shop completion.
I PM'd you when you have some time.
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on November 25, 2016, 08:34:29 PM
I have completed the setup of both shops used for engine building. The photos show some of the tooling used for finished chromed aluminum cylinders. The chroming process has been developed to give a very high quality cylinder wall with .00005" roundness. More to come on this process.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Admiral_dk on November 25, 2016, 09:54:15 PM
Glad to see you back Jim and will be looking forward to more education from you  :praise2:

Best wishes

Per
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: 90LX_Notch on November 25, 2016, 10:12:49 PM
Glad to see you back Jim and will be looking forward to more education from you  :praise2:

Best wishes

Per


X2, I really find this thread facinating.

-Bob
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on December 01, 2016, 12:46:29 AM
The first photo shows a complete chroming tank with heaters. The chrome tank is maintained at 130 deg. F & is run at a current density of 3 amps/sq. in. The total current required for the brass holding fixture & the liner is 24 amps. The brass holding fixture prevents the build up of chrome on the top & bottom of the liner. This build up takes place on the fixture & is removed afterwards with a warm 50% solution of HCL acid. At a current density of 3 amps/sq.in., .0012" of chrome/side/hr. will be deposited. In 2 to 2.5 hrs., a total of .0024"+ of chrome will be deposited on the liner's inner wall. If done properly, this simple bath will deposit smooth chrome with a hardness of 1,000 Vickers. Carbide tooling WILL NOT cut even 900 Vickers Chrome.

The second photo shows a Simpson DC amp meter & volt meter with hook up wires plus an on-off switch.

The third photo shows an Astec model LPS-252 switching power supply. The power supply has an output of 3 to 6 volts at 50 amps with +-2% regulation & a 50 mv ripple.

More explanations to follow.

JA
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on December 01, 2016, 12:53:37 AM
Here are some photos of the inside of the fixtures used to chrome brass or aluminum cylinders. The last photo are samples of aluminum cylinders that I chromed today.

JA
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Roger B on December 01, 2016, 09:25:43 AM
Fascinating work  :ThumbsUp:  :ThumbsUp: I'm still learning  :headscratch:
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on December 02, 2016, 03:18:08 AM
These photos show the chroming tank in operation. The entire tank is placed inside a foam cooler which helps to stabilize the tank's internal temperature. The positive voltage is connected to the anode & the ground is connected to the cathode (liner inside wall) where the chrome is deposited. This particular cylinder is for a .45 cu in engine. It requires 11.5 to 12 amps at 3.8 to 4.2 volts for 80 minutes to give enough chrome build up for the final honing process.

JA
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on December 09, 2016, 10:28:59 PM
This is how the fixture is supported in the chroming tank. Notice the two silicon coated wire leads (cathode) passing through the tanks cover that are connected to the cylinder sitting inside the brass holding fixture. Also notice the 1/4" lead antimony (anode) which supports the entire unit & is held in place with a split collar. Quality rubber gloves & a respirator type mask are used at all times when using the chrome tank. There will be some chrome that plates on the holding fixture's inside wall (through transfer & exhaust windows) & at the top & bottom of holding fixture. The build up at the top & bottom of the fixture prevents any unwanted buildup at the top or bottom of the cylinder. Any plating on brass pieces is removed by placing those pieces in a 50% solution of warm hydrochloric acid.

Next will come the necessary chemicals & the procedure needed for successful chrome plating of aluminum alloys. Most engine manufacturers prefer to chrome plate brass cylinders because the only required cleaning solution is an alkaline wash. THIS IS NOT THE CASE WITH ALUMINUM!

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on January 30, 2017, 07:17:05 PM
The necessary chemical solutions needed for the successful chroming of aluminum alloys must be kept in polypropylene containers with polypropylene covers. Quality rubber gloves, a respirator type oxygen mask, rubber apron & face splash shield are also used at all times when handling these chemicals. All chemicals are mixed according to volume only. The special holder shown in the upper right hand corner of photo #1 allows the cylinder to be placed in the solutions & rinsed without any contact.

1. Mix 1 part Hydroflouric acid with 3 parts of  Nitric acid.
2. Mix 2 parts of Zincate with 1 part of distilled water
3. Mix 1 part Nitric Acid with 1 part of distilled water.

Since the cleaning, etching  procedure is time sensitive, a clock & the necessary time lengths are posted in clear view.

1. Place the cylinder in solution number 1 for 30 seconds. Remove & rinse in hot tap water.
2. Place the cylinder in solution number 2 for 40 seconds. Remove & rinse in hot tap water.
3. Place the cylinder in solution number 3 for 5 seconds. Remove & rinse in hot tap water.
4. Place the cylinder in solution number 2 for 120 seconds. Remove & rinse in hot tap water.

Place the cylinder mounted in the fixture in the heated chrome tank with the power turned on. The tanks temperature is maintained at 125* to 130* F. The starting current is 1/2 the amount needed to give a total of 3 amps/ sq in. For the area of theses cylinders 6.5 amps is used for 5 minutes & then the current is raised to 13 amps for 75 more minutes. The full current amount is calculated from the total area of the cylinder & its brass holding fixture divided by the current to give 3 amps/ sq in. The 75 minute plating time gives approximately .001" to .0015" of chrome/ side.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on April 24, 2017, 02:45:48 PM
The hard chroming process is not complete without proper honing or grinding of the plated surface. At Aero Precision we use a Sunnen Honing machine & the simple holding fixture shown to quickly hone cylinders round within .00005" & also to the correct taper. Each cylinder is checked during the honing process with a Sunnen bore guage to tight tolerances.
 
Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Admiral_dk on April 24, 2017, 09:48:02 PM
Seeing all that it involves to fabricate one of these marvels makes one realize how fair the price actually is compared to the normal sport engine.

Again thank you for showing us  :NotWorthy:
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on April 24, 2017, 10:17:01 PM
I'm also deeply involved with the development of tuned pipes for nitro and gas engines. Some of the chambers being tested are rolled & others are machined from thick walled tubing. This is another story to be told, maybe some day.

JA
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Admiral_dk on April 25, 2017, 12:55:30 PM
Expansion chambers for two-stroke engines are another very interesting subject for some of us here, so I got a question :

I have seen several software programs that can calculate two-stroke engines from 50cc and up, but never any for smaller engines - so do you calculate your own or is there a program I haven't seen ?

By the way - very nice looking system you are building in the pictures above.
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on April 27, 2017, 08:17:28 PM
I use 2 Stroke Wizzard 5 only as a reference, but always keeping in mind what has been learned from many hours of dynamometer testing. For example, a calculated chamber for a single cylinder 26 cc engine operating in the 19,000 to 22, 000 RPM range would have a major diameter of 2.455" & a baffle cone angle of 27*. Actually the best tuned pipe for my application would have a major diameter of 2.5" to 2.7" & a baffle cone angle of  22*. Another important consideration is the volume of the chamber in comparison to the displacement of the engine. No single program that I know of gives an absolute answer as to what would work best.

The photo shows the next section of the diffuser before it is parted off. A .010" deep X .050" long undercut will be machined before the piece is parted off. One more section after this & the chamber will be ready for silver soldering. Notice the heavy, water soaked  brown rapping paper inserted "tightly" inside when machining the OD. It changes the chatter frequency & allows the piece to be machined down to a .022" thick wall without any chatter.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Admiral_dk on April 28, 2017, 11:37:12 AM
Thank you very much Jim

I just ordered the software at $35 until May 1st. it's a no brainer for software that includes model engines - admittedly not diesels (CI) but I can live with that. I expect that some of the problems / differences you encounter has to do with the fact that you can't tell the program what exhaust temperature you have, but "only" chose fuel type - still for a program this cheap, no problem  :)

Thanks for the trick with the paper - nice to know  :ThumbsUp:

Best wishes

Per
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on April 28, 2017, 01:26:17 PM
Sorry for getting off the main topic here. In order to make effective use of the necessary chemicals involved in hard chroming plating of aluminum alloys, the simple cylinder holding fixtures shown were made from 1/8" diameter soft aluminum rod. Only the cylinder & its holding fixture are inserted in the chemicals for the specified amount of time. The only other contact with the cylinder is when it is removed from this fixture before being placed in it's brass holding fixture. This is done with rubber gloves by touching only the cylinder's lip! This may sound complicated or difficult, but it is really very easy to do when the holding fixture is properly made. The holding fixture also makes it very easy to wash the cylinder & the 1/8" diameter holding fixture in hot tap water in between each insertion in the chemicals.
 
Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: lohring on April 28, 2017, 03:01:18 PM
Expansion chambers for two-stroke engines are another very interesting subject for some of us here, so I got a question :

I have seen several software programs that can calculate two-stroke engines from 50cc and up, but never any for smaller engines - so do you calculate your own or is there a program I haven't seen ?

By the way - very nice looking system you are building in the pictures above.

All tuned pipe formulas are at least partially empirical.  Gordon Blair published a program years ago that most of the newer formulas copied.  My current favorite is from Frits Overmars based on the drawing below.  Be sure you have some idea of the average exhaust gas temperature in the pipe.  The only way to check a design without building it is an engine simulation program.  Even so I believe there's no substitute for dyno testing.

Lohring Miller

http://www.underdogsracing.com/fospipe/
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Roger B on April 28, 2017, 06:54:28 PM
It's interesting that the Field Marshall tractor with a 6 litre 750rpm single cylinder two stoke diesel that is the basis for my model also has this exhaust pipe geometry.

I will have to look into this  :headscratch:
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Admiral_dk on April 28, 2017, 07:19:58 PM
Jim and Lohring - Thank you very much to you both. I'm not going racing as such (I did that in my youth), but I'm still very interested in at least getting a good starting point - and it will be a lot better than no exhaust system anyway  :)

Roger - nice beast - but I would be very surprised if a pipe of that the length / dimensions actually boost the power by any significant amount  ;)
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: lohring on April 29, 2017, 02:34:39 PM
I've made and tested quite a few pipes.  We actually made a pipe that delivered less peak power but more rpm for a record trials engine.  Two stroke's characteristics depend heavily on the tuned exhaust.  The above formula is for peak power at a given rpm. Guessing the mean temperature is based on experience.  I once designed a series of pipes with too high an assumed exhaust temperature.  They were all too short and it showed in dyno testing.  Alcohol fuels have a lot lower exhaust temperature than gasoline.

Lohring Miller
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Admiral_dk on April 29, 2017, 06:55:12 PM
Lohring - it is actually possible to measure the exhaust temperature at almost any position in the system so you can remove the guesswork if necessary.

You can use a "K Type Thermocouple Sensor" as they have a range of −200 C to +1350 C (−330 F to +2460 F).

I've meet a former Scandinavian Road Racer champion that told me he installed those in the exhaust port of the cylinder and in the combustion chamber to measure the temperature there to check the jets in the carburettor and these can be placed in the exhaust at different positions too. He cold see the temperature increasing as they went down the main strait and used that to program how much the ignition box opened the power jet to add extra fuel.

I'm sorry if I'm telling you what you already knows.
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: lohring on April 30, 2017, 04:07:39 PM
We did measure the temperature.  We took a value that was too close to the exhaust port.  Since the speed of sound varies with temperature, deciding on the temperature that will give the correct speed is the issue.  I suppose it would be possible to measure the temperature at several different points and average them, but we never did. 

However, actual running conditions will give varying amounts of pipe cooling which again makes a difference.  We deliberately injected water into the header to, in effect, lengthen the pipe for more low rpm power.  The system gives a two speed transmission effect that works so well in model boats that one club outlawed it. 

I finally came to use the temperature as a more abstract value that is related to the brake mean effective pressure.  The higher the output, the higher the temperature.  Moving the pipe along the header is used to compensate for small pipe temperature changes.  Pipe design is still an art to some degree. 

My favorite experimental pipe had a movable baffle cone section.  We could move the diffuser along the header and hold the baffle cone position constant.  It turns out that the diffuser position isn't particularly critical.  The baffle cone position is what determines the tuned length.   The pipe's volume changed with the length of the band section, though.  The diameter is the variable I use to set pipe volume.    I barely scratched the surface in pipe design, but there was no substitute for actual engine dyno testing.

Lohring Miller
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on April 30, 2017, 04:47:19 PM
All of Lohring's posts are correct & factual. Even after extensive dyno testing, it may be necessary to make changes to the initial design when it is placed into actual running conditions. It is virtually impossible to change one factor without effecting some other factor or factors. During dyno testing I have measured temperatures as high as 990*+ F at the header & 450*+ F at the mid point of the tuned pipe. What temperature should be used in any of the formulas used to calculate the tuned length? As Lohring stated when the pipe is in actual use the internal temperature is constantly changing. Tuned pipes made from computer programs never seem to work as designed without some modifications.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on April 30, 2017, 04:49:58 PM
Machining of the third section's ID is done with a 3/4" X 10" boring bar. This section has the same .010" deep X .050" wide relief inside to enable interlocking with its mating second section. The OD is machined by mounting the piece between centers because of it's long length (4.100").  After final machining all pieces are shown interlocked for easy silver soldering. Next comes the all steel header & its 5/16" thick steel mounting flange, which are also silver soldered together. No type of rubber "O" ring or gasket is used between the engine's crankcase & the steel mounting flange. There is no leakage at this point!
 
Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Admiral_dk on April 30, 2017, 06:02:44 PM
Quote
All of Lohring's posts are correct & factual.

Oh - I'm not questioning any of you - au contraire  :praise2: to me there's a big difference between experience + testing and theory. So much so that I might know quite a bit about the theory on many subjects in Science and elsewhere, but I only have deep knowledge / experience on a few subjects => You might not necessarily surprise me when I think about what you tell me, but I wouldn't have figured most off what you tell me by myself.

So again - thank you a lot both of you  :praise2:
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on May 01, 2017, 01:58:10 PM
The final header section, which is also tapered, is being test fitted before final silver soldering. A special aluminum cradle, with clamping device, will be mounted beneath the mid section of the pipe. It will have a soft neoprene rubber nest for the mid section of the pipe to rest in. Several different length center sections have been machined to allow tuning of the tuned length without shortening of the head pipe area.
 
JA
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: lohring on May 01, 2017, 02:52:26 PM
I just read a post by Frits Overmars that summarizes my approach to pipe design.  He was answering a request for an appropriate speed of sound for a particular engine.

"That's not a serious question, is it Daisy? Because if it was, I would need to know about a hundred things regarding your engine before I could give a more or less accurate estimation.
Just pick a value between 350 and 550 m/sec, build a pipe, see where the rpm of maximum power is, and if it is not where you want it to be, adapt your picked value accordingly. If your first pipe isn't already in the ball park, your second one should be. It's not that difficult."

We used this approach to get a pipe that took an 9 hp engine to 11 hp.  We shortened the header and center section on the stock pipe along with some intake timing changes.  That raised the peak power rpm from 17,000 to 20,000 rpm.  We wanted even more rpm so I designed an even shorter pipe for high rpm power.  We lost one hp off the peak but got a better power curve, especially when we added water injection.  The engine began to show signs of mechanical failure at 25,000 rpm so we limited it to 23,000 rpm.  There would have been more power available at higher rpm.

Lohring Miller
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Admiral_dk on May 01, 2017, 08:42:05 PM
I'm very impressed with the short Miller pipe with water  :ThumbsUp: but also a bit mystified with the big dip between two peaks on the rest of the curves ....
I know that power curves aren't flat although that is what you want on almost all racing vehicles with direct transmission to tarmac - any ideas about why they have such big a dip ?
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: lohring on May 02, 2017, 12:56:40 PM
The thought at the time was poor carb metering over the rpm range.  The engine, a CMB 35, ran a Tillotson carb, and we had a variety of problems with it.  The engine was used to set straight line records so high rpm and idle performance were the only issues.  The water injection smoothed everything out.  To get the engine to idle well under load in the boat we ended up blocking the non adjustable low speed circuit jet with super glue. 

Below is an rpm versus time graph taken during an acceleration run from the data logger.  Note the plateau at 20,000 rpm with the water on.  Turning it off allowed 23,000 rpm.  The graph represents a speed of around 50 mph in the beginning to over 90 mph.  We later got an onboard GPS for speed, but the peak speed during that series of tests was by a radar gun.

Lohring Miller
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Admiral_dk on May 02, 2017, 07:18:07 PM
93.1 mph. - woa - I'm very impressed as these speed on water where thought as almost totally impossible in my youth  :praise2:

That highest speed on water I knew of back then where the Danish Navy Torpedo-Boats - 3 gas-turbines @ 12000 HP and 55 Knots, one 75mm. canon, torpedo's, rockets and a few machine guns.
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: lohring on May 03, 2017, 11:28:38 AM
This is a model boat, and not our fastest.  We held the gasoline engine record from 2004 until last year at 110 mph with a 26 cc engine.  The lighter weight more than made up for the more powerful 35 cc engine.  Our only full size boat record is with an electric boat set in 2008.  See -yNu2_LlO9st=6s  So far it is still the world's fastest at 98+ mph though much better electric power plants are available today.

Lohring Miller
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on May 05, 2017, 03:24:58 AM
In the beginning of this topic I failed to explain in detail exactly how aluminum parts were to be physically cleaned before being placed in the three chemical baths used. After very light de-burring of all the cylinder window edges with a very sharp Exacto knife, a brush hone, hot water & full strength Dawn is used to wash the ID of the cylinder. Moving the brush hone up & down as it rotates removes anything that may be loose in the cylinder's ID or at the edges of any window. The cylinders are then thoroughly washed in hot water with the circular fine hair brush shown.
 
Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Roger B on May 05, 2017, 07:18:13 AM
By 'Brush Hone' do you mean a 'Flexi Hone'?
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on May 05, 2017, 02:19:54 PM
Yes, Roger. They come in many different sizes & they will not damage the machined finish. I normally do several passes while rotating from end to end, washing in hot water until the cylinder & flexi hone are both clean.

JA
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Kim on May 05, 2017, 09:09:46 PM
The items shown in your pictures don't look like a Flex-Hone.  They look more like what I'd call a 'bottle brush' or something.  Not for honing, just for cleaning.
Kim
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on May 06, 2017, 06:51:29 PM
When I return to work on Tuesday, May 9,2017, I'll get the exact name & part number.

JA
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on May 09, 2017, 11:50:01 PM
The honing device shown in post # 224 is a soft nylon deburring brush. The tool is impregnated with 500 grit aluminum oxide & is available from EngineHones.com.

JA
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on May 13, 2017, 01:49:45 PM
I'm beginning the machining of a rubber isolated, cradle type tuned pipe mount for this boat. Both the tuned pipe & it's mount will be rubber isolated. The engine's steel exhaust flange & header has also been completed. No type of "O" ring or gasket is necessary for positive sealing.
 
JA
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Admiral_dk on May 13, 2017, 07:36:46 PM
Two things immediately comes to my mind :

It looks like noise dampening isn't a problem where you race it - I know that the expansion chamber lowers the noise a good amount on certain frequencies and the rest can be lowered by quite an amount with a simple light absorption muffler at the end of the stinger ....

It looks like you use springs to hold the expansion chamber in place, if I "read" the last picture right - though they aren't there yet - or ?

And a bit of curiosity about the boat - is carbon fibre the normal material now ?

Is the hull a "catamaran" like a number of full size racing boats ?

Size and weight ?
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on May 13, 2017, 10:06:13 PM
Noise is not a problem on the 30 mile long by 2 mile wide lake we use. The actual noise generated at WOT is a measured 110 DB's at 50 feet. A Muffler can lower this to 85 DB's at the same distance. I use springs as well as a machined teflon piece with hose clamps to hold & seal the pipe, header joint. The photo shows a similar set up as to what will be done for this tuned pipe, header connection point. Carbon fibre is not the normal material used because of it's high cost. This hull, a catamaran type, is an infusion molded type done with a vacuum pump. The hull weigh 6 LBS & is 48" long X 17" wide.

JA
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on May 16, 2017, 11:27:37 PM
The tuned pipes flat section is not parallel to the top of the radio box, therefore a 7* angle is machined in the cradle as a first step. I rough cut the cradle & located it with the round plug on the rotary table. Custom made toe clamps securely holds the cradle for final machining. The adjustable clamp is held in place on both inside ID's  of the cradle with 3/32" OD pins which are located in pre-machined holes. These holes are driled after the cradle's  7* angle is machined & they are also drilled at a 7*angle. The 3/32" OD pins are silver soldered to the adjustable clamp pieces a small distance from their ends. Once they are inserted, they can only be removed by being driven out with a 3/32" OD pin. The final rubber isolation pieces will be glued in place with high temperature silicone rubber cement. The cradle will also have lightening holes machined in it's base.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Admiral_dk on May 17, 2017, 09:43:39 PM
Quote
Noise is not a problem on the 30 mile long by 2 mile wide lake we use.

I see how lucky you are in that respect - here there's a mile maximum to the nearest house, no matter wich Danish lake we choose ....

Nice cradle  :ThumbsUp:

Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: DRT on May 24, 2017, 02:26:08 AM
 (http://www.modelenginemaker.com/index.php?action=dlattach;topic=3890.0;attach=64633;image)
Very beautiful watercraft and 2stroke gas pipe you have here James. :praise2: What a stinger!! Doing all you own hardware too? Are you running a flex shaft or articulated drive...and how's the cowling like the pipe? Have you fitted it yet?

Also what have you put together in a new SAW pipe for the .90 nitro methane engine?

Yours Truly,
The puppy...
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on May 25, 2017, 03:39:08 AM
The pipe fits perfectly under the cowling. There is a possibility I will use a solid drive with the ball & pin universals I have used for many projects. I haven't done anything with the nitro engine except to set up a troidal head. I'm wondering how you know about the articulated drive system that I used previously?

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: DRT on May 25, 2017, 06:16:33 AM
Lol,
That's easy James. I have many of your prints, and the list of materials for toroidal heads, the tools that need to be made to turn the universals, connecting rods, double roller needle bearings etc. You sent them to me....and its all filed away for future reference.

I'm curious after you mount the pipe where does the cg sit on that catamaran from the transom? That will need to be worked out to avoid a blow over. I doubt the maker of that hull has mounted and run anything as powerful, or quite like the setup you have there with the pipes length and all considered. When you get it set up I'd love to come to falls lake to hear and see it run.

TTYL....
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on May 25, 2017, 09:35:23 PM
The CG will be 17" to 17.5" from the bottom of the rear running surfaces going forward. This will be set up with everything in the hull, including fuel, special sparking coil (8 ozs), radio box with radio gear, fuel tanks with fuel, tach, all hardware mounted on the transom, drive train, etc., etc. This hull is long at 48", therefore if too much air gets trapped underneath, it will become a kite.

Why are you hiding your name "Mr. Puppy"? I remebered the title from another site.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: DRT on May 25, 2017, 09:49:29 PM
James you know this is Hubert or did you forget you directed me here to see the work you were doing. DRT stands for Daimler Robotics Tech! Definitely not hiding as I told you my handle through PM here when I arrived. Guess you forgot.
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: DRT on June 01, 2017, 05:31:34 AM
If you get the chance I would like to see the Toroidal head you cut for the .90 engine. Did you mill it or create a turning tool for the lathe? Will the Toroidal head change what would be the optimal tuned pipe for the motor?
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on June 01, 2017, 09:00:08 PM
I do not see any change to the optimal pipe design. Maybe this is happening because the engine's operating temperature for both the gas & nitro engines did not increase a siginificant amount. Remember that the star characteristic of the Toroidal design is the elimination of any detonation at very high compression ratios. The interesting thing is that the Toroidal design seems to work the same in both types of engines. I searched for the print of the toroidal head used on the .90 cuin nitro engine. It is similar to the chamber used on the gas engine because the ID's are close to the same. 1.339" for the gas & 1.125" for the nitro. I used the same size ball nose mill but at a different location from center. Milling of the chamber is done on a rotary table. Be carefull with the milling as small changes with chamber size & depth can make a difference.

JA
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Admiral_dk on June 01, 2017, 09:54:10 PM
Jim are your drawings supposed to be rotated around the "centre of the plug" so to speak ?

If so, what is the "curved" line under the plug with any dimensions in the top drawing - the top of the piston or a reference line ?
If not - not much squish band or ...?

On the bottom drawing you seem to have three different curves for the "roof" - does that mean that you got a "multi-shaped roof" ?
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: DRT on June 01, 2017, 11:16:57 PM
Maybe I'm wrong but I think the line is the top of a domed piston. This leads me to ask which style piston gave you the most increase in performance when used with the Toroidal head? I guess in the nitro motors a flat top is the only thing available from manufacturers of boat motors so you'd almost have to get into machining your own pistons if you wanted any thing else.
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on June 02, 2017, 12:33:15 AM
The curved line in the top drawing is the piston crown of the gas engine. The straight line in the bottom photo is the piston crown of the nitro engine. Notice that the ground straps & the tip of the center electrode is .015" away from the piston crown at TDC. Most engine builders cannot believe this does not cause a hot spot on the piston's crown. Also there is no death ash visible on the underside of the piston. The radius on the piston crown helps to cool the piston crown because the incomming charge will attach to it. Also look at how close the glow plug will be to the piston at TDC in the .90 cuin nitro engine. The dimension is what would be found in .45 cuin engine.

I have not looked at the difference in performance between a flat top piston & a curved piston. The two engines operate at very different RPM ranges, different deck clearances, different squish velocities, different fuels, etc., etc. The flat top pistons used in the nitro engines & the domed pistons used in the gas engine are both custom machined.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on June 02, 2017, 01:03:05 AM
When you compare this drawing of some of the original Toroidal heads tested in gas engines, it will be obivious that there has been a substantial increase in the engines compression ratio without detonation problems. Concentrate on the figures indicated in red. These niumbers are where the next to last head design was tested. Notice the depth of the chamber & its location from center written in red. The photo shows the actual piston crown & head after many hours of running.

JA
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on June 19, 2017, 11:11:19 PM
The original tuned pipe's center section of 2.750" in length, was reduced in steps down to 1.000". This is easily done by un-silver soldering sections that are machined to fit inside each other & re-maching the undercut areas with the fixture shown previously. This change allowed the engine RPM's to reach 20,600+. We also increased the oil content from 12 ozs/gal to 14 oz/gal. By shortening the center section's length instead of shortening the head pipe's length, the bottom end & mid range torque were unaffected. However, the tuned pipes total volume & tuned length have been decreased. Also with increasing the engine's RPM & power, there is a narrowing of the engine's maximum power band. There was also an increase made to the engine's cooling system.

JA
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Admiral_dk on June 20, 2017, 11:43:02 AM
Very interesting Jim - I wouldn't have thought of "just" shortening the centre part as the best way to go  :ThumbsUp:

I just realized that I somehow missed that you're using a lot of bolts to hold the head in place - I can't remember ever seeing anything but four bolts for the cylinder + head on all racing two-strokes over 50cc - but you use TEN  :o
I'm guessing that you do this to prevent distortion of the head ....

Again thank you very much for sharing your expertise with the rest of us  :praise2:
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: lohring on June 20, 2017, 02:32:41 PM
I built a pipe with a variable center section as well as a variable length header.  That allowed testing the variation in diffuser and baffle cone position separately.  It turns out that the diffuser position isn't very sensitive and that the tuned length is determined by the baffle cone position.  Below is a dyno graph with a fixed header length and different center section widths compared to an M&D pipe.

The pipe was designed with a high horn coefficient diffuser to deliver a large "suction" pulse that overcame the intake restrictions in earlier Zenoahs.  It added nearly 20% more power.  Later intake and transfer modifications reduced this restriction and the pipe worked the same as a standard pipe.  It is still a good pipe for stock Zenoahs.

Lohring Miller
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Admiral_dk on June 20, 2017, 09:45:10 PM
Thank you very much for the curves Lohring - rather informative   :praise2:

The end before the "stinger" - is that a "strong point" for the support of the adjustable length or a cone going down to the smallest diameter and a bigger diameter tube leaving as suggested earlier and if so, why is it followed by the smaller diameter tube ?
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: lohring on June 21, 2017, 01:33:45 PM
The fat end of the baffle cone is threaded for a screw in stinger.  We tried several different stinger diameters as well as an inverted stinger.  An inverted stinger goes back into the pipe to the center section, quieting the pipe.  Our testing showed the same power as the standard position.

Note the difference in the diffuser section on this pipe compared to Jim's.  This pipe has a high horn coefficient.  Pipes designed for peak power have a lower horn coefficient, that is the diffuser doesn't flair as much.

Lohring Miller
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: DRT on July 13, 2017, 11:08:33 PM
Hi Jim,
I saw on another site someone suggest to you ultrasonic cleaning to prepare your pistons for fitting. I would advise against this for pistons made from aluminum. I use Ikohe E60H and E 300 H Elmasonic ultrasonic cleaners at work to clean the paint bell cups that spin at 60K on the Sames electrostatic paint applicator bells fitted to the 7 axis fanuc machines I service at Daimler. At 37Khz these machines can peak nearly 2 hp of energy and erode certain materials due to cavitation. This cavitation was enough to pit an aluminum bell cup we tested. The titanium ones one the other hand held up. This is enough to lead me to believe that the results on an aluminum piston and other types of metals and materials would be less than satisfactory! This may explain why their cleaning tanks are made from cavitation resistant stainless steel and why Bob has no problem cleaning dental tools with them.

Take Care....
 
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on July 16, 2017, 12:44:35 PM
Very good information my "Puppy",

Even engines that have been buried in the ground at a 200 MPH speed are washed in a 50% solution of Ultra Dawn & Super Strength Greased Lightening. A hot water rinse brings all the aluminum & steel parts back to like new condition.

JA
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: DRT on July 24, 2017, 10:12:01 PM
 :Lol:
Hi James,
Just curious on your tuned pipes what octane gas and percentage nitro methane are your gas and nitro pipes optimized for respectively?
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on July 25, 2017, 03:41:10 AM
I use ethanol free, regular gas from the pump in my gas engines. There are some gains to be found with oxgenated fuels, but this would be illegal. I use HP-2 in my gas engines with 10 to 14 ounces/ gallon. My nitro engine uses 80 % nitro methane, 12 % ethylene oxide & 8 % oil. The oil is 2/3 Klotz & 1/3 Blendzall racing cartor.

JA
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: lohring on July 25, 2017, 02:35:40 PM
We tested a lot of different fuels over the years.  The fixed head 26 cc gasoline engines don't benefit from much but the lowest cost fuel.  You need to be able to optimize the compression, ignition timing, and especially the pipe design for each fuel.  When you can only change the mixture the graphs below show what happens.  Note that the ethanol fuels seriously lower power if you don't richen the mixture.  The variation in peak power is probably not significant, though but there is variation in the low end and over rev area.  By the way, the tested E10 was actually 30% ethanol, the E85 was 60% ethanol and the 92 octane was 8% ethanol.

Lohring Miller
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: DRT on July 25, 2017, 08:29:53 PM
We tested a lot of different fuels over the years.  The fixed head 26 cc gasoline engines don't benefit from much but the lowest cost fuel.  You need to be able to optimize the compression, ignition timing, and especially the pipe design for each fuel.  When you can only change the mixture the graphs below show what happens.  Note that the ethanol fuels seriously lower power if you don't richen the mixture.  The variation in peak power is probably not significant, though but there is variation in the low end and over rev area.  By the way, the tested E10 was actually 30% ethanol, the E85 was 60% ethanol and the 92 octane was 8% ethanol.

Lohring Miller

Thanks Lohring,

The main reason I asked Jim the fuel question was because I wanted to know which fuels he was actually optimizing his pipes for. On the topic of alternative fuels it makes sense that you'd have to richen the ethanol fuels. I think this is what kind of defeats the novel idea that they would be the wave of future fuels in automobiles when you have to basically double the mixture as opposed to gasoline to do the same work. Essentially you'd also save no coin at the pump.  I had a flex fuel Tahoe but never tried it because everyone I talked to said their flex vehicle ran terrible with it.

BTW
Have you done any work with toluene as a fuel in a two stroke? Also have you contemplated a workable FI system for a 2 stroke in the displacements run in the RC boating organizations?
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: lohring on July 26, 2017, 02:42:12 PM
You could argue that all the tuned pipe glow ignition engines are throttle body fuel injected.  Pipe pressure forces fuel into the carb.  Since pipe pressure varies with power output, this is a very crude regulating mechanism.  In the past crankcase pressure was also used.  Jim has used this same system on gasoline fueled spark ignition engines, but we mostly stuck with modified Walbro pumper carbs.  They gave problems at high rpm even with lower pop off settings and other tweaks.

We did not experiment with any gasoline additives other than the methanol and nitromethane we had on hand.  We mostly wanted to convince ourselves that fuel cheating wouldn't give big power gains.  Since these tests some other additives have been suggested, but we never tried them.  Below is the article I wrote on the testing.

Lohring Miller
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Admiral_dk on July 26, 2017, 09:33:58 PM
Thank you for showing the full article - it helped understanding the graphs even better  :ThumbsUp:

Best wishes

Per
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on August 10, 2017, 11:48:49 PM
Mr. DRT,

I'm unable to use the articuulated ball & pin universals on this project because there would be an excessive angle where the stuffing tube exits through the bottom of the hull. Placing the engine as far forward & as low as possible made the use of a cable drive necessary. Sometimes you gain in one area only to lose in another.

JA
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: DRT on August 28, 2017, 10:34:29 PM
Thanks for the update. With that hull and motor you probably have a legitimate shot at a gas cat record if you can hold it in the road. I'm curious will the skeg be a hindrance in all out speed endeavors? Do you plan on using the new carb setup on it with the pipe?

In the meantime I hope you're willing to share photos and how you find the engine timing numbers, without a degree wheel, that you enter in the pipe programs you use to build the pipes. I think the real engine builders here will appreciate it and actually have the know how to apply it in their own DIY engine projects versus the average off the shelf consumer.

It was never explained by OE consumers how "precise measurements are made" for the numbers that would used with the Employee Assistant Programs... sorry I meant Engine Analysis Programs. :Doh:
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: lohring on August 29, 2017, 01:06:15 PM
There are a lot of available piston position calculators available.  Attached is one.

Lohring Miller
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on October 02, 2017, 10:07:19 AM
After successfully chroming approximately 1500, #4032 aluminum cylinders, I will show the final changes made to the #360 free machining brass, cylinder holding fixtures. Each fixture could be used twice to chrome a cylinder. There are reasons I prefer not to do this. The build up of chrome on chrome that takes place behind the cylinder ports on the brass holding fixture & the build up of chrome on chrome that takes place at the top & bottom of the brass holding fixture. Since this build up of chrome must eventually be removed  from the brass holding fixtures, any decrease in the amount of time required in the HLC bath is desirable.

I will post the photos latter.

Jim Allen 
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: DRT on November 08, 2017, 03:21:28 AM
James,

I truly hope you and Lohring continue share the things you learned here about performance two stroke engines and how to build them. This seems to be a much better place to receive intelligent questions, and have your intelligent responses be accepted. It's increasingly tiring to have the passing of knowledge from people like Fritz Overmars, and yourselves repeatedly sidetracked by individuals that have nothing better to do than complain about it's usefulness due to their lack of understanding and/or ability to build the parts necessary!

Thanks for all you do,
Hugh

Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on November 10, 2017, 11:26:57 PM
Hugh,

I have been taking some time off to get things in order. Getting ready for a possible move in the East direction to be closer to the running sites. Working on a special rudder setup for the cat. No problems with the situation you referred to. Catch you latter.

Jim
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on November 29, 2017, 11:06:28 AM
Lohring Miller will be looking at how his engine analysis program results compare to the actual dyno & on lake performance of the new tuned pipe chamber. He has found that previous tests of the tuned pipe used on the out rigger type hydroplane & the computer analysis are very similar performance wise. This is a big help when attempting to build tuned pipes in the future because it gives a direction to start with.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Admiral_dk on November 29, 2017, 11:45:18 AM
That is very interesting news  :praise2:

I use simulation tools for a lot of my professional work - designing music equipment http://www.emmaelectronic.com/ (http://www.emmaelectronic.com/) so I really appreciate the difference between accurate models and all else  :ThumbsUp:

I expect that you still need to measure the exhaust temperature of the engine in order to get the simulation as close as possible - considering what Lohring has disclosed so far in earlier post in this thread.

Looking forward to more info on this subject  :)
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: lohring on November 29, 2017, 01:48:17 PM
I use a program called EngMod2T.  (http://vannik.co.za/EngMod2T.htm (http://vannik.co.za/EngMod2T.htm))  As you noticed, it needs a very careful input of temperatures and other data to give accurate results.  I compare its results to the extensive dyno data we collected over the years.  It tends to be a little optimistic  because 26 cc engines have larger friction losses as a percent of power compared to say 125 cc engines.  It's really helpful in evaluating tuned pipe designs.

Lohring Miller
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on February 04, 2018, 02:25:38 PM
The two tuned pipes shown in the photo are similar, but they are used on different hull types. The chamber painted black is used on a rigger & the un-painted chamber is used on a cat. Both are used for oval racing. Their major diameters are the same, but the tuned length of the unpainted chamber is longer. This longer tuned length is because of the smaller included angle of the baffle cone used on the un-painted chamber. Also the unpainted chamber has no straight flex section & a much shorter flanged header section. Both chambers have a total internal volume that is approximately 24 times the displacement of the engine. A very important fact that allows the use of a long, small ID stinger for the maximum boost amount possible!

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: lohring on February 04, 2018, 03:42:52 PM
I just recently came across a very interesting tuned pipe calculation spreadsheet.  It's for the highest performance engines with a bridged or triple exhaust.  It calculates both the pipe and the exhaust passage from the piston into the pipe.  This is all empirical, but is based on some very experienced two stroke engine builders experience. 

Lohring Miller

Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Old School on February 20, 2018, 09:30:35 AM
I am interested in your work on tuned pipes, I don't know much about the boats you run. Will the boat accelerate and come onto the pipe without any any outside assistance?

I run tethered cars but we have a guy in the centre who will horse them up to a speed were the pipe will start to work and the car then accelerate away that speed is around 100mph.
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Admiral_dk on February 20, 2018, 11:22:10 AM
I thought that the trend with tethered cars now was to use variable exhaust ports as in the full sized engines - so you start with a low port and opens the port as speed increases  :noidea:
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on February 21, 2018, 09:55:43 AM
I am interested in your work on tuned pipes, I don't know much about the boats you run. Will the boat accelerate and come onto the pipe without any any outside assistance?

I run tethered cars but we have a guy in the centre who will horse them up to a speed were the pipe will start to work and the car then accelerate away that speed is around 100mph.

I am familiar with tether car type tuned pipes. They are usually made of steel or titanium, never aluminum, because of the high "G" forces (10 to 12 times the cars weight) that the car will be subjected to when running at its maximum speed. I visited the track located on Long Island many times when I lived in Huntington, L.I., N.Y. I have witnessed speeds over 200 MPH by racers such as Guitterio Picco & Mats Bohlin in the .60 cu in class. Other well known racers such as Jan-Erik Falk, Nils Bjork, Rune Granberg, John Ellis, Jack O'Donnell, Erik Strobel & others from around the world competed in the world class events held there. This track was developed & sponsored by Dr. Anthony Tucci. It is one of the best tracks in the world! Many of these racers visited my machine shop located in Huntington.

All tuned pipes are similar & they work on the same principles. With that said, be aware of the infinite diffuser angles & lengths, baffle angles & lengths, major diameters & lengths, stinger ID's & lengths that could be used in making a tuned pipe.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: DRT on February 21, 2018, 08:46:38 PM
James,
 I'd like to switch gears for a minute and ask about the billet block construction of these engines. Did you possibly use a broach to cut the crankcase transfers in these?  Are you willing to share photos of the transfers and or the process to cut them? Beautiful work BTW.

 (http://www.modelenginemaker.com/index.php?action=dlattach;topic=3890.0;attach=18650;image)
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on February 23, 2018, 12:01:47 AM
Okay.

I have to get the necessary drawings & photos together in order to give an understandable explanation.

Please be patient?

JA
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: lohring on February 23, 2018, 02:58:20 PM
You can find a lot of Jim's work pictured in the International Waters gallery (sign in required).  He has great explanations under the pictures as well.

See http://gallery.intlwaters.com/index.php?cat=10141

Lohring Miller
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on February 24, 2018, 12:00:39 AM
The cutting of the transfers was never explained fully because this was a proprietary process at that time. No other bar stock, one piece, engine crankcase  at this time could be made with the entire transfer profile being cut from the inside. The final size, depth & shape of the transfers was developed with the cut & try method.

We learned that the thickness of the cylinders wall not only has a greater influence, but is the determining factor, on what direction the incoming & exiting gas must travel. The photo shows what can happen if the radial or axial angles of the transfers are cut incorrectly in a liner which has the proper thickness!! The red lines are the radial angles cut on the main transfers closest to the exhaust window. Re-cutting the angle on the main transfer windows closest to the exhaust window from 33 deg 30 min to 43 deg 30 min eliminated this problem. Final dyno test of this .80 cu in engine showed 6.2 to 6.8 HP at 24,000 to 26,000 rpm on 65% nitro fuel. I used this engine, with the re-cut liner and new piston, to set my first NAMBA straight away record at the NAMBA Nationals in Washington, DC in 1990.

JA
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: DRT on February 24, 2018, 03:21:33 AM
Lohring,
You don't have to be signed into intlwaters to see Jim's gallery or explanations. Thank goodness..... His IW gallery has had its own google link for years now.  Just type in Google's search bar Jim Allens .90 engine


Yes James,
 I knew it was proprietary and not included there. We talked about it years ago... I have all the patience in the world. Thanks in advance....

Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: lohring on February 24, 2018, 03:37:03 PM
That's good news.  I'm signed into International Waters so I automatically assumed that it was required.  More people need to see how to build high performance engines.  The art is being lost.

Lohring Miller
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on February 25, 2018, 04:30:55 PM
I forgot to mention that while the engine was running at WOT, the center post of the glow plug began to glow red. It was Bill Wisniewski's suggestion to recut those main transfer angles to eliminate this problem. In fact, with the angles re-cut at 43 deg 30 min,  the engine could be over leaned at WOT without burning the plug out. This also taught us that the directions of the incoming charge will have a great effect of how much compression the engine can stand before detonation sets in. The better control of where the incoming charges were being directed was a direct result of changing the wall thickness of the cylinder from .060" to .125". Everything else in the engine was the same!!

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on March 17, 2018, 08:18:44 PM
Sometimes it becomes necessary to repair & modify a favorite tool. The Fowler ULTRA-CAL II electronic caliper was disassembled & has the 5 original permanent rivets replaced with 5 precision machined removable rivets. This allows the entire unit, including the P/C board, LCD & wipers mounted in the calipers cover to be easily removed for deep cleaning. The caliper works as well as it did when purchased 25 years ago. Its calibration has been checked.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on May 27, 2018, 04:25:07 AM
James,
 I'd like to switch gears for a minute and ask about the billet block construction of these engines. Did you possibly use a broach to cut the crankcase transfers in these?  Are you willing to share photos of the transfers and or the process to cut them? Beautiful work BTW.

 (http://www.modelenginemaker.com/index.php?action=dlattach;topic=3890.0;attach=18650;image)

Here are some photos of the boost ports & main transfers. The tops of these ports were cut first & then the remaining material was broached with a special tool to be shown at a latter date. The darker colored crankcase, which was made of steel, used the same techniques to cut the transfers from the inside of the cylinder. Drawings of the shape broached into the cylinder walls will be shown at a latter date. The .200" thick lip used on the cylinder lowered the crankcase height by this amount which made cutting from the top possible. More details on this to follow.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: DRT on May 30, 2018, 12:18:24 AM
Thanks a lot for sharing this information. Nice work!  :happyreader:
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Admiral_dk on May 30, 2018, 11:46:10 AM
Thank you again Jim for sharing.

I have a few questions though. On bigger engines there's usually 4 main transfer ports and one or two boost ports, but you have three boost ports and only two main transfer ports ... why ?

One of the pictures show the main transfer port and the top looks to be turned a bit toward the exhaust - is that a slightly blurred picture, an optical illusion or perhaps the earlier mentioned adjustment of the main transfer port to avoid overheating the plug ?

Best wishes

Per
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on May 31, 2018, 10:37:47 PM
The reason I used 3 boost ports & 2 main ports is because the design was copied from the the OPS engines I ran before building my own engines. I discovered later on that what was done as far as the radial & axial angles machined in the cylinder was much more important in controlling the directions of gas flow. I discovered this by accident when the typical cylinder wall thickness was changed from .060" to .100". None of the transfer valleys in the crankcase are turned in any radial direction as is shown by the posted prints & they are all the same depth. However, there are many different radial & axial angles cut in the .100" thick cylinder wall on the boost, main transfer & exhaust windows. Duplicate windows that match in the cylinder's wall must be siamese twins in the radial & axial directions.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Admiral_dk on June 01, 2018, 12:13:26 PM
Thank you again Jim.

The tool showed looks like you use it as a broach ..?.. and if I read the drawing correctly, you have bigger transfers / boost channels in the block than in the liner - I always made sure I didn't have any ridges / edges in the flow - or am I reading them wrong ?

Best wishes

Per
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on June 04, 2018, 08:40:07 AM
Per,

Yes, the tool is used as a broach to cut the 3 boost & 2 main transfer passageways in the crankcase. Yes, the width of any transfer passageway in the crankcase is slightly larger in the radial direction than the width of any matching liner window. However, the top of any transfer passageway will match exactly the top of any liner window. The machining of the crankcase passageways is done on a rotary table with the fixture shown & the windows in the liner are cut with a dividing head. All dimensions concerning the engine timings are calculated mathematically. No degree wheel is ever used! I posted some prints to show the types of calculations required to modify or build an engine. Since this type of engine does not have a piston ring, the taper used in the cylinder & the top taper used on the piston can be determined only by trial & error. As a general rule, the shorter the stroke, the higher the taper on both & vice versa. I machined tapers in .001" increments to find out what was best for the stroke used.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on June 04, 2018, 08:43:03 AM
More photos.

JA
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on June 04, 2018, 08:43:52 AM
last photo.

JA
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Admiral_dk on June 04, 2018, 11:57:02 AM
Thank you very much for clarifying everything Jim  :praise2:

Quote
Yes, the width of any transfer passageway in the crankcase is slightly larger in the radial direction than the width of any matching liner window. However, the top of any transfer passageway will match exactly the top of any liner window.

So essentially you have a tapered transfers - that makes quite good sense and that I didn't get all the details out of the drawing first time.
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on June 05, 2018, 01:01:15 AM
Per,

Yes. However transfers shaped with a radius inside & outside have proved themselves to be better than anything used thus far. These type transfers have proved themselves to be better than the standard "tea cup shaped transfers". The posted photos show what a transfer with a radius inside & outside looks like. Transfers with a radius inside & outside cannot be machined but must be cast into the crankcase.

JA
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on June 05, 2018, 02:06:09 PM
Per,

One very important function of any main transfer design is in its ability to help attach the incoming charge to the piston's crown. In my engine the main transfers were flat on the top & the piston's crown was also flat on top. The engine with the radius type transfers uses a domed piston crown to help attach the incoming charge to the piston's crown. Cooling the piston crown in this way, combined with a toroidal head design, allows for very high compression to be used, without detonation. More on this subject latter.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Admiral_dk on June 05, 2018, 10:17:43 PM
Jim,

Your last tree cylinder pictures has transfers and ports that are shaped as I would expect a modern racing two-stroke (or very close to) and I'm guessing this is a 26cc gasoline engine. Your cylinder does not look very different to my nephews Yamaha YZ 80 with 28Hp except for cooling and size.

When I did a lot of tuning in my youth, I only cared about the gas flow (+ inlet and pipe) and I had a very low compression on most of my engines but still a lot more power down the straight than a Yamaha 80cc MotoX racer of the time from a 50cc and time and knowledge has increased quite a bit since then (the Yamaha had 8-10Hp back then and 28Hp today).
I used a water faucet as a source of a visible "gas" and corrected my ports until I was satisfied with the angles and lack of disrupting turbulence, but I never changed the transfer port angles in the cylinder wall (had no proper tools to do so) and did not encounter any problems - most likely down to my low compression (7-8:1) and about 12-13Hp => not nearly as highly thermal stressed.

I can see why your attention to angles are important in relation to not only flow, but also to cooling and gas boundary layers (insulation) in order to keep the thermal loads / stresses in check at the most important places like piston crown and combustion chamber + plug ..... and I never got that far, before money ran out back then and I stopped racing .... but the subject still fascinates me quite a bit.

Per
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on June 05, 2018, 10:31:50 PM
Per,

Actually the last photos are from the MV .45 cu in FAI racing engine. These engines operate in the 35,000 to 38,000 RPM range. The transfers are copies of the type of transfers that are used in the 125 cc Aprilia racing engines. They make use of the Coanda gas flow principle.

JA
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on June 18, 2018, 07:03:23 PM
Per,

The photos are of the 50 cc Bidalot engine cylinder. They are examples of what needs to be done in 26 cc to 35 cc high performance engines. Notice how thick the cylinder wall is, the number & shape of the ports, their location & the radial, axial angles involved.

JA
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Admiral_dk on June 18, 2018, 11:37:44 PM
Hi Jim

I'm rather surprised, or should I say that the wall thickness is even greater than the biggest I seen so far - but I can certainly see that it will provide a smooth and fast flow when changing direction. The port shape on the inside of the cylinder wall is very similar to the Aprilia 125 and the only difference to my nephews YZR80 is the bottom of the exhaust.

Thank you very much for the pictures.

Per
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on June 19, 2018, 01:24:02 AM
Hi Per,

Yes & the head shape is similar to the Toroidal shape used on the 125 cc Aprillia. I use a Toroidal head on my 27 cc gas engine. One of the main features of the Toroidal head design is a very high resistance to detonation when high compression is used.

Jim
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Admiral_dk on June 19, 2018, 10:16:03 PM
Hi Jim

Quote
One of the main features of the Toroidal head design is a very high resistance to detonation when high compression is used.

I thought that it as almost mandatory for any serious high performance two-stroke design for the last few decades. You have posted your drawings here earlier in this thread, but I must admit that though I seem to remember seeing somebody posting the formula for the shape somewhere, but I can not remember where that was - do you have any suggestions for somebody reading this thread in the future (or me)?

Per
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on June 23, 2018, 10:56:30 PM
High Per,

The starting point for my engines was to machine a toroidal head shape that had a volume which was much less than a typical hemi head. I continued to lower the toroidal head shape until it could not be lowered any more. The volume in this head is less than 1 cc. I could not lower this head anymore because the ground strap of the spark plug was .016" away from the piston crown at TDC. There was no evidence of detonation, death ash or high engine heat when running at WOT.

JA
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Admiral_dk on June 24, 2018, 09:33:22 PM
Hi Jim

That is extremely compact and a very small volume as you mention  :o

Very impressive that it burns so clean too  :ThumbsUp:

Per
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on June 25, 2018, 06:44:54 PM
Per,

I have a much smaller volume toroidal head button which uses a semi-surface discharge type spark plug. The idea for making the plug originated from Lohring Miller. Since the toroidal head shape will not go into detonation as other head types will do when overcompressed; the question to be asked is when is the engine overcompressed? Knowledgeable two stroke engine builders & tuners taught me to look for the engine RPM's sagging in the over-rev range beyond peak HP. With the testing done thus far it would appear that this information is valid. The photos show that head with its semi-surface discharge type spark plug which has the same heat range as the standard type spark plug. One problem with this type spark plug, which has the electrodes coming from the side, rather than underneath the center electrode, is the area where spark ionization takes place will be exposed to the incoming charge. I eliminated this problem with the use of a very powerful secondary coil.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Admiral_dk on June 25, 2018, 07:22:00 PM
Jim

Quote
One problem with this type spark plug, which has the electrodes coming from the side, rather than underneath the center electrode, the area where spark ionization takes place will be exposed to the incoming charge. I eliminated this problem with the use of a very powerful secondary coil.

I would have thought that the extreme combustion pressure was the reason for the higher voltage requirement (Law of Physics), but I can also imagine that extreme turbulence (otherwise very desirable) could more or less prevent building the ionizing layer between the electrodes, until an extreme voltage is reached ....  :noidea:

I'm curious as to how high a compression ration did you reach here ?

Per
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Roger B on June 25, 2018, 07:34:52 PM
I'm still following along although this is beyond my experience  ::)  :ThumbsUp:  :wine1:
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on June 26, 2018, 07:52:36 PM
Per & Roger,

I never bothered to calculate the exact compression ratio. However, the toroidal heads that I use have less than 1/2 the volume of a standard hemi head for this size engine. I do run compression checks as the engine ages. Typical readings of 150 psi tell me the engines single piston ring is good.

Jim
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: AlexS on July 06, 2018, 07:10:56 PM
150 psi looks like a lot for a two stroke! May I ask what kind of compression ratio are you running?
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: lohring on July 07, 2018, 03:26:18 PM
Thanks for the plug credit.  Ideas are cheap and easy, but the actual execution deserves all the credit

Lohring Miller
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on July 08, 2018, 07:21:16 PM
"One problem with this type spark plug, which has the electrodes coming from the side, rather than underneath the center electrode, is the area where spark ionization takes place will be exposed to the incoming charge. I eliminated this problem with the use of a very powerful secondary coil."

The photos show the original placement of the 8 0z+ black secondary coil mounted between the front engine mount arms. This mounting position completely threw off the CG of the hull, which necessitated the mounting  position shown in the latter photos.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Admiral_dk on July 08, 2018, 09:03:04 PM
150 PSI  :o  :o very impressive Jim  :praise2:

OK that goes a very long way towards explaining the high tension voltage requirement and then add the gas swirl inside the combustion chamber, we get there :zap:

Per
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on August 05, 2018, 10:14:07 AM
Per,

I haven't had the necessary time to update the latest information concerning the tuned pipes. I will do this when time permits. The tuned pipes are becoming more like the stuff used by high performance two stroke engine builders!

JA
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Admiral_dk on August 05, 2018, 09:48:00 PM
No worries Jim.

But I will admit to being curious about the "end" off one of the stingers - never seen anything like it before.

Per
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on August 15, 2018, 08:41:25 PM
150 psi looks like a lot for a two stroke! May I ask what kind of compression ratio are you running?

Alex,

When using the Static Compression Ratio Calculator, the static calculated compression ratio is 14 to 1. This calculated number may even be higher at the time of this writing because there have been further reductions to the toroidal head's volume. Since the engine shows no signs of going into detonation at WOT, which is the main characteristic of a toroidal head shape, further reductions in the heads volume may be possible. Also, there is no sign of the engine sagging off in the over-rev range, which would indicate the engine is overcompressed. I'm not sure what influence the latest tuned pipe design has on whats taking place.

Jim allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on August 15, 2018, 08:47:50 PM
No worries Jim.

But I will admit to being curious about the "end" off one of the stingers - never seen anything like it before.

Per

It's a simple design, low restriction type muffler. The stingers ID & length will determine how much restriction can be used without raising the engines operating temperature at WOT. Haven't looked at the DB reduction for this type muffler, as yet.

JA
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on August 15, 2018, 09:12:54 PM
It's interesting to see the performance differences that are possible when small changes are made to similar type tuned pipes, which are being used on the same 26 & 27 cc engines. The three pipes shown have different power curves, different peak HP amounts, different peak HP band widths & different over-rev characteristics. I believe all shown could be applied to oval type racing.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Admiral_dk on August 16, 2018, 11:44:41 AM
Quote
It's a simple design, low restriction type muffler.

Ah - I didn't realize this - thank you for the explanation. I have only used absorption mufflers and only seen that type on two-stroke racing bikes too.
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: DRT on October 25, 2018, 10:02:57 AM
Hey James I have to switch gear for a moment but we need to talk. Email of call me Asap!
(https://psp-tsp.com/Images/Defense%20Research%20Services/Quad4animResized.gif)
Detonation has a very useful application thats extremely powerful. I'm sure you will appreciate this!
Say hello to the pulse detonation engine.
https://psp-tsp.com/index.php?id=203
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on October 26, 2018, 08:27:55 PM
This is very interesting, considering that  one of the main enemies of any compression ignition engine is detonation.

Jim
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: DRT on October 26, 2018, 09:01:38 PM
Isnt it? I thought so too. I knew you'd want to see this.

http://www.aero-news.net/index.cfm?do=main.textpost&id=08312146-cc40-476d-a000-57401f63f5b9

don't want to pull you guys off this interesting thread but Im sure you all will find it quite interesting how detonation is being used as a friend instead of the enemy.  Really cool technology is.

Email you later JA
TTYS
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on November 25, 2018, 04:35:54 PM
After testing many different tuned pipe prototypes we can finally show a dedicated chamber for use with 32 to 35 cc displacement gas engines. The bottom two prototypes will be going into production for this purpose. The posted photo clearly shows the difference between what is available on the market & what is necessary in an attempt at achieving maximum HP. A tuned pipes maximum internal volume, compared to the displacement of the engine in question, is definitely one  controlling factor in the design of any tuned pipe!

Jim Allen

Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Admiral_dk on November 25, 2018, 09:53:04 PM
It might be the light or eyes deceiving me, but - is the bottom pipe in the picture having a continuously changing angle on the first diffuser cone ?

I ask, because I always felt that this would be the optimum, just like when used for sound (speakers, trombone etc.) or fluid dynamics (turbines etc.), where any kind of sharp edges are usually a no, no ....
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on November 27, 2018, 06:50:37 PM
Per,

Yes. We attempted to make a smoother transition from the header pipe through the diffuser sections to the mid-section by adding more pieces. Instead of the standard 2 or 3 sections found on most pipes there are 5 sections in the diffuser section. What is important is that there is no long length flat area from the exhaust window to the mid section of the chamber. The next thing is to CNC machine the sections to eliminate any flat area whatsoever.

Jim
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Roger B on November 27, 2018, 07:03:51 PM
Fascinating  ::)  :headscratch:  :ThumbsUp: There is so much to learn about two stroke engines
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Admiral_dk on November 27, 2018, 08:07:27 PM
Ah and I thought that it was hydroforming as the first photo didn't show the welds of the cones but looked like it was two sheets welded end to end and then "blown up" to shape.

Very nice work none the less  :ThumbsUp:
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on November 28, 2018, 05:17:55 PM
Ah and I thought that it was hydroforming as the first photo didn't show the welds of the cones but looked like it was two sheets welded end to end and then "blown up" to shape.

Very nice work none the less  :ThumbsUp:

No Hydroforming but two pieces formed in a mold & then welded together. This is not the best method for making a prototype pipe because it cannot be easily modified or changed. Machined pipe sections are fitted to join inside or outside of their matting pieces. This method makes a completely smooth inside surface & a very strong joint even when the joint is silver soldered. The joint is typically .050" wide with each joining piece's thickness cut in half, typically .010" thick.  This method can also be used when joining sections that have a radius.

Jim Allen

Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on February 22, 2019, 09:33:55 PM
Finally got the shop put back together. There are more than 20,000 screws in the inventory plus dowel pins, washers, nuts, rolled pins, etc., etc.
Building & re-building the necessary engines for this season. The last photo's are the new assembly, disassembly die being made.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on February 23, 2019, 11:35:21 AM
I'm building a new die set for the assembly & disassembly of three piece crankshafts. After assembly they will be zeroed within + or - .0002" from end to end in a four jaw chuck.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: lohring on February 23, 2019, 04:23:56 PM
I don't know how you keep your shop so neat.  Too many projects and boats in too little space.  At least I found the chuck key on the mill table.

Lohring Miller
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on February 23, 2019, 06:53:17 PM
Lohring,

I finally finished cutting three sets of 1/16" thick, #9850 Garlock gasket material, which is used between all the surfaces on the intake side. The gasket material is composed of carbon fibers with a nitrile binder. Maximum temperature of 900* F &  a maximum continuous temperature of 650* F. I carefully re-machined the delrin isolation block to match the 19 MM carburetor bore.

This stuff should take care of the sealing on the intake side. Oh, I forgot, the two extended water fittings are enlarged & they are made of 6AL4V Titanium.

Jim
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: lohring on February 24, 2019, 05:10:12 PM
I've been playing with a Tillison clone carb with a 21 mm venturi bore in simulations.  Intake tuning helps a little as well.  Below are the formulas I found.

RPM = 108K ( 1st hamonic ) 97K ( 2nd harmonic ) 54K ( 3rd harmonic )  / L ( inches )
 
So examples are 1st Harmonic 6000 rpm = 18",and 12,000 rpm = 9"
                            2nd Harmonic 6000 rpm = 16.16" and 12,000 rpm = 8.08"
                            3rd Harmonic 6000 rpm =  9" and 12,000 rpm = 4.5"
Rearranging the above:
L=54,000/rpm for the third harmonic.

The higher rpm we run at makes the 3rd harmonic realistic.  At 18,000 rpm that would be 3" or 76 mm.  We found that a little shorter isolator block helped Zenoahs at high rpm.  Velocity stacks were too long and hurt power.  I think Quickdraw has experimented with intake tuning as well.  Our engines came with several thick gaskets that we were told not to change. 

Lohring Miller
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Admiral_dk on February 24, 2019, 08:21:06 PM
Very interesting formula, but it "breaks Math" as the definition of Harmonics is :

1 + 1/2 + 1/3 + 1/4 + 1/5 + 1/6 + 1/7 + 1/8 + 1/9 + .....

Fundamental + second + third + fourth + fifth + sixth + seventh + eight + ninth + .....

So where does the 2/3 as the second and the 1/2 as the third come from ?

Or are "real harmonics" part of the "original formula" in such a way that it solves into what you wrote Lohring ?

I'm NOT trying to say that the formula doesn't make sense or isn't useful - it is more a definition thing.
If it was music, the 2/3 interval is one of the most important harmonics and is funnily enough named the Fifth (as it is the fifth note in the Major Scale).
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on February 24, 2019, 10:15:27 PM
Lorhing,

Very interesting numbers! I have not lengthened or shortened the length of the intake track since I began modifying theses engines. Everything is in nearly the same position, including the throttle arms, as when the engines came from QD. This would include the Walbro & .625" bore automatic fuel metering carburetors. All of the systems are using tuned pipe pressure, but the 19 mm Tillotson carburetor uses both tuned pipe pressure & the crankcase pulse. My pulse line is very short & very rigid. One area that is very different is the smooth transition between the rectangular shaped intake window (.845" X .480") & the round 19 mm (.748") hole. Their areas are also similar, .406 sq in ( rectangular window) to .439 sq in (round hole). The total length of the intake track has remained at approximately 3.500". The engine is now making more HP in the over rev range beyond 19,600. The difficulty with shortening the length is that it can only be done in the delrin isolation block.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: lohring on February 25, 2019, 02:35:17 PM
I think harmonic is a misnomer.  The formula refers to wave lengths.  The first "harmonic" is the length needed to allow for the reflected pressure of a full wave to return to the intake port.

Lohring Miller
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: dieselpilot on February 25, 2019, 04:17:23 PM
Do you know how these factors are derived, or a source? Google turned up something, but it was conflicting and no mention of how it was derived.
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: lohring on February 26, 2019, 06:32:14 PM
I'm not sure how they were derived.  My source is a restricted two stroke forum.  I've tested the 3rd harmonic length in a simulation and it helped the power some.  Serious tuners have dyno tested intake tuning on a variety of engines.  The problem is it only helps a little over a restricted rpm range.

Lohring Miller
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: MJM460 on February 27, 2019, 02:45:13 AM
I am normally another silent onlooker, but I am really enjoying this thread and in total admiration of the amazing work being done.  But perhaps I can contribute to the vibration question.

The motion of a violin string and similar systems is often referred to as simple harmonic motion.  The equations of motion are simple enough to be derived in junior physics classes, and all the solutions which have stationary nodes at the fixed points at the end of the string occur, and are simple multiples of the first natural frequency.  This the rich sound of a stringed instrument.  The vibration is at right angles to the length of the string.

In a long pipe with many supports and bends, like in a petroleum refinery, there are many such natural frequencies for each pipe, and they are related to the different lengths between the fixed support points, so are generally not simple multiples of each other.  So just different natural frequencies rather than simple harmonics.  The equations of motion are no longer simple, and the natural frequencies come from a form of finite element analysis, which is definitely not simple.  However computer programs are used to calculate the natural frequencies, or the frequencies at which any motion will tend to be amplified by resonance, and are used extensively where there is a regular forcing vibration, for example in reciprocating compressor piping.

Inside the pipe, either a gas pipe in a refinery or an engine exhaust pipe, there is longitudinal motion of the gas column, which is seen as pressure pulsation, and also experiences resonance at certain frequencies where a standing wave occurs.  These natural frequencies are again not simple multiples of each other but relate to different features of the pipe which give rise to a reflection, such as a bend or a change of diameter.  Some of the resulting standing waves result in a low pressure at the pipe end, helpful for an engine exhaust, while others result in a high pressure at the end and not so helpful.  The frequencies require a finite element analysis of the gas system, and are not simply derived.

The trick is to design the exhaust pipe so that a standing wave will occur with a low pressure at the engine exhaust port, at a frequency corresponding to the engine speed where the power boost is required.

In addition, the resonance can be very strong over a very narrow frequency range, or less strong but significant over a wider frequency range.  A sharp mountain peak compared with a rolling hill if you like.  For an engine, you want the rolling hill, so there is assistance over a wider rpm range, and you dont want one of the patterns with a high pressure at the exhaust port.

There is no simple formula to predict the frequencies, it is again done by computer with a finite element technique.  Unfortunately not a programme most of us would have access to unless we are in a formula one team, or a University fluids mechanics department.  And it may be just as easy to find the frequencies by trial and error. 

The effectiveness of tuned pipes is well known.  I assume that the typical conical features, used in a tuned pipe for a single cylinder engine, by providing a gradually changing diameter, contribute to making the resonance less pronounced, but effective over a wider rpm range.

I hope that is a little help to understanding what is going on.

MJM460
 
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: dieselpilot on February 27, 2019, 02:00:42 PM
The theory is not in question, just how it was boiled down to a simple factor. Tuned pipe doesn't work in that exact manner, but close enough for general discussion. It appears the 108K factor is simply the resonant frequency of the length of the intake with some corrections and is not the fundamental, but the 2nd harmonic already. I don't understand why the 3, and 4th don't follow the expected pattern as Admiral_dk pointed out already. Google turned up several series of these factors and two completely unrelated methods of intake tuning.  Tuning to the fundamental gives the largest increase, so the 3rd or 4th give smaller improvements. Chances of randomly picking a short length (for 18kRPM) and being close to the 3rd,4th harmonic are pretty good. So, unless the initial length tuned it with negative results, you may not see much improvement. Not knowing what correction factors are included, it would be easier to dyno with a telescopic intake....
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: lohring on February 27, 2019, 03:56:41 PM
The simulation program I use, EngMod2T, divides the engine and its pipes into small volumes and calculates the changes between these volumes from basic principles.  It doesn't simulate combustion or actual scavenging flow but is accurate in modeling pressure, flow velocity, and mixture purity through an engine.  Combustion and scavenging are determined by empirical models backed by lots of real world testing.  This engine model was developed first by Gordon Blair at the Queens University of Belfast and has been refined ever since. 

Most pipe design formulas found on line are empirical.  They are a good starting point.  The simulation gives a more realistic version of what really happens.  I and others have confirmed this with dyno testing.  The intake tuning formulas are also empirical.  However, the calculated length gives more power in the simulation.  We also did some tests on two available isolation blocks.  The stock length was best until the power curve was shifted into higher rpms.  A shorter block gave a little better power there.

Lohring Miller
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on February 27, 2019, 08:24:05 PM
"Not knowing what correction factors are included, it would be easier to dyno with a telescopic intake...." do you have any practical ideas on how to make a telescoping intake track, considering what the track presently looks like?

JA
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: dieselpilot on February 28, 2019, 01:48:19 PM
The types I've seen were adjustable length velocity stacks. They would be of limited range when the stack is short. Regarding intake tuning, inertial effects are independent of acoustic and probably more important at high speeds. I've not looked into how to tune for it.
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on February 28, 2019, 08:57:37 PM
I have varied the total length of the velocity stack from .600" to .900" on various bore sizes. All were shaped (bell mouth) to give the maximum flow. None showed any appreciable difference in performance on my dyno. I wonder if the reason is because of the small amount of difference or the dynos inability to read the difference.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: lohring on March 01, 2019, 02:01:25 PM
The only dyno test we did on intake tuning involved two different isolator blocks on a modified Zenoah.  We always found that velocity stacks reduced power.  Below is the test.  Note that the M&D carb on the standard isolator block was as good as my carb on the short block.  Also note that it's hard to separate any differences from the scatter.  We mostly ran the stock isolator block as a result.

Lohring Miller
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: dieselpilot on March 01, 2019, 02:44:27 PM
Any change in diameter in the intake causes a reflection. If the carb has the typical venturi, it comes into play. The bell shaped stack also influences the resonant frequency of the system. The smooth bore carb might make it easier to find a sweet spot, if one exists, in the range of manifold length you're willing to run.
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Admiral_dk on March 01, 2019, 07:33:36 PM
I wonder (without knowing) if the Helmholtz resonance frequency of the whole system has more influence then than the "outside" resonance.
The reason for my thinking are the fact that some Two-Stroke engines has shown that they will continue running even when they inlet valveing stops working at high rpm's, because the Helmholtz resonance is very strong at that frequency and if this is the case, it could be much stronger than the "outside" system .... :thinking:
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: lohring on March 02, 2019, 03:38:12 PM
That's called a 24/7 intake system.  One proposal uses a reed valve for low rpm that swings out of the way at higher rpm.  One model boater started and ran a standard race engine with the intake valve removed just to prove it could be done.  See uSubC3Gu-Bscontext=C3bacfcdADOEgsToPDskLxCTbBGuDPWU-hTqHEvnrC  Motorcycle racers have finished races with a disk valve that failed open.  Below is an illustration of the principle.

Lohring Miller
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on March 02, 2019, 05:06:12 PM
This was originally discovered by go-kart racers who ran reed valve induction systems. If the reeds failed while the engine was running, it continued to run. I'm unaware if the engine could be easily started & throttled properly. I'll look into what was said on the TWO STROKE TECH site about this.

JA
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: DRT on March 03, 2019, 10:10:23 AM
I have varied the total length of the velocity stack from .600" to .900" on various bore sizes. All were shaped (bell mouth) to give the maximum flow. None showed any appreciable difference in performance on my dyno. I wonder if the reason is because of the small amount of difference or the dynos inability to read the difference.

Jim Allen

It doesn't matter really James. Like your test stand shows. If you can turn the same load faster with the same reliability or better as the motor before it you have a more powerful motor and that would certainly show on the dyno. The stacks are beautiful to really make more power or better tunability with them, based on the manifold bore diameter and cyclic input velocities involve, the length of the stack, taper, and bell mouth that also needs to wrap around towards the back of the muzzle shapes have to be optimized by mathematical model or some other means of flow analysis.

@Lohring,
All you have to do is take the scatter plots and connect lines of best fit and then you can see better your data variations and comparisons. Excel should have this ability. Also are you checking seeing which regression most accurately fits you data points? You should also be able to toggle between the data points and lines of best fit. Power, Logarithmic, Cubic, etc all have a  linear regression, so there will be one that likely fits your data best.

BTW I have some electric motors and ideas for your boats I know you'd love.

I miss you guys and think about you often. I'm also finally at a lathe and mill where dreams can happen. Big things going on now and more to come in the near future. Happy 2019.

Thanks,
Hubert
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: DRT on March 03, 2019, 10:15:48 AM
Jim
Have you ever run any of you saw nitro props on your gas engines?  And have you ever considered a rotary attachment similar to your helical pitch gauge to mill your own props? I'm very sure with your skills you could do something similar to this.You have access to cnc and if you dont you will soon.  ;) You'd mill both side out of a block. I def don't have to tell you how to reference position.

(https://www.onthewire.co.uk/images/SC-Props-1.jpg)(https://www.onthewire.co.uk/images/SC-Props-2.jpg)(https://www.onthewire.co.uk/images/SC-Props-3.jpg)

"These are made in the Ukraine by multiple champions Andreij and Volodymyr Smolnikov. The props are custom CNC machined from both sides in the blocks as seen to whatever diameters and pitches are specified. The rectangular block is a group of A2 in varying sizes and the circular block A3 props showing the machining from either side. A1 sizes are also on offer. Props are available either as a block at a sizeable discount or finished and ready for use. The blades in the block are finish machined to very high tolerance, a matter of microns, with just a small spur at the tips and more substantial fillets on the boss keeping them in position."

~on the wire uk~

Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: lohring on March 03, 2019, 03:52:07 PM
@Lohring,
All you have to do is take the scatter plots and connect lines of best fit and then you can see better your data variations and comparisons. Excel should have this ability. Also are you checking seeing which regression most accurately fits you data points? You should also be able to toggle between the data points and lines of best fit. Power, Logarithmic, Cubic, etc all have a  linear regression, so there will be one that likely fits your data best.

I did that as well as average the data from at least three runs.  Some of my plots have these average lines on them.  Our early tests had more scatter than our later tests, but the dyno's precision was about +- .1 hp.  I measured the standard deviation between several identical runs at between 1 and 3%.  Scatter plots keep people from making conclusions from the data that aren't justified.

Lohring Miller
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: lohring on March 03, 2019, 03:58:48 PM
I built a helical fixture to mill props.  I haven't used it, though.  It's described in the article at http://namba.com/content/library/propwash/2014/April/#/4/ 

Lohring Miller
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on March 03, 2019, 05:48:53 PM

Jim
"Have you ever run any of you saw nitro props on your gas engines?  And have you ever considered a rotary attachment similar to your helical pitch gauge to mill your own props? I'm very sure with your skills you could do something similar to this.You have access to cnc and if you dont you will soon.  ;) You'd mill both side out of a block. I def don't have to tell you how to reference position."

The answer to all of these questions is absolutely no! There isn't enough time available to address in depth propeller making. I have posted some photos of what is presently being worked on. It is true that the carbon fiber prop test stand saves time, but I'm only looking at what happens at WOT settings.

Jim  Allen

Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: DRT on March 04, 2019, 05:42:35 AM
@Lohring,
All you have to do is take the scatter plots and connect lines of best fit and then you can see better your data variations and comparisons. Excel should have this ability. Also are you checking seeing which regression most accurately fits you data points? You should also be able to toggle between the data points and lines of best fit. Power, Logarithmic, Cubic, etc all have a  linear regression, so there will be one that likely fits your data best.
I did that as well as average the data from at least three runs.  Some of my plots have these average lines on them.  Our early tests had more scatter than our later tests, but the dyno's precision was about +- .1 hp.  I measured the standard deviation between several identical runs at between 1 and 3%.  Scatter plots keep people from making conclusions from the data that aren't justified.

Lohring Miller

Hi lohring,

Have you determined which regression has the best coefficient of correlation and determination to your data? This not the average of the data point you've taken from several runs. If your building a graph piecewise from data  which you have to be if its's taken on an inertial dyno there's no point to be worried about the variance in accuracy of line smoothing. Accuracy is already at the will of how well you build it from piece wise from discontinuous data which will certainly have variance. The linear regression doesn't have to have line smoothing per se and if you have selected the one with the highest coefficient of correlation and determination it will be as accurate any any scatter plot you have. It is built from you scatter data and gives you the line that actually fits it most accurately. When you want clear visual representation to compare data this is the required way.People should never make conclusions from just the data points or lines on a graph. It should be teamed with real world results as well as other confirming mathematical models. They should all be fair agreement to feel confident about making any assertions thereof.

@Jim,
A reaction torque sensor mounted on a linear slide on axis with the motors shaft with a propeller forced into a load cell with a tach should tell you what you want to know at wot. The setup can be hobby grade or IEEE grade simply using  "TEDS" sensors that meet the IEEE 1451.4 protocol. Your other option is an eddy current brake . You can use an induction motor with magnets and a copper disk in a touchless design and VFD with braking resistors. The torque cradle previously described is really all you need to see improvement though . You can certainly mount an inertial disk to the motor versus a prop. You may need to build a carbon fiber retention sleeve. You wrap it on an undersized arbor. Finish it to final od an length on the lathe and press fit it on the flywheel which you can make from 304 stainless, titanium, or Inconel 718 SPF @(1393 MPa). A undersized fit of .134mm with the carbon fiber sleeve will give you a zero speed pre stress pressure of 476.6MPa.It has to be balanced of course. I have a lot of information on these kinds of things but your a difficult man to get in touch with just a state a way. So I give you a little here without getting too off topic.

(https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcSwSwQpCPRlyCGb1XpO1Qq2pZIBb4dBYojr6iZ_Z1bMuOmZwz4IEQ)
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Admiral_dk on March 04, 2019, 11:24:49 AM
Jim has a very high accuracy water brake - see earlier in this thread.

But some of the rest of us might find a cheaper / simpler measuring device interesting - more details please - though maybe in a separate thread.
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: DRT on March 04, 2019, 01:56:01 PM
Hi Admiral,
Have no fears. Jim is a close friend Im very aware of all he has. Using Teds sensors means it's accurate enough to be approved by the IEEE. Look up the TEDS system and understand all it entails. It's alot more than just an accurate sensor. It has to do with stringent calibration schedules etc. He has a water brake but the sensor system I suggest isn't something that was available when he adopted and upgraded the brake from Ed Kalfus. It also speaks to the transformation from raw data the brake measures to what is visually represented through graphs charts etc. The brake is not fun to use without this side of the coin fully integrated. No one want to write down data points and derive regressions time after time. He needs a self working data acquisition software package to do this work automatically. There is no question I can help him complete that side of the coin.  Cell or registry math in MCU's brains are more my thing. U need these things for instance like a dedicated optical tach to get what the water brake reads easily up on the screen so he can simply examine a graph versus having to build it after every pull of his various dyne meters.

Jim and Lohring are both well respected highly valued technical minds in our sport. I know them both quite well away from here. They have both taught me many things about the subject matter at hand. I only consider my offering as paying it forward. I'll be more than happy in time to show you in a separate thread  that side as I develop my electric motors.

Thanks,
Hubert
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Niels Abildgaard on March 04, 2019, 04:37:24 PM
Jim has a very high accuracy water brake - see earlier in this thread.

But some of the rest of us might find a cheaper / simpler measuring device interesting - more details please - though maybe in a separate thread.

Aircraft engines has been tested for ages with  rotating wood blocks

http://4.bp.blogspot.com/-2DEoFo4Va9g/VfctF7G_DtI/AAAAAAAAP2c/FVKGF4-vSP0/s640/MOULINET_COLOMBAN-RENARD.gif (http://4.bp.blogspot.com/-2DEoFo4Va9g/VfctF7G_DtI/AAAAAAAAP2c/FVKGF4-vSP0/s640/MOULINET_COLOMBAN-RENARD.gif)
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on March 05, 2019, 04:39:51 AM
I wouldn't use any thing made of wood or glass filled nylons to test my engines. The photos show the last test stand I built which can test both gas & nitro engines on the same test stand. The loading devices are carbon fiber propellers of various pitches & diameters. They are cut from existing Falcon brand propellers & re-balanced in a magnetic balance. The same shafts with ball & pin universals are used for both type engines. This test stand weighs approximately 35 lbs & must be secured to the bench during WOT runs at typical RPM's of 20,000 to 30,000+. No torque is measured with this test stand. I load the engine to give the same RPM as measured on the water. I typically run an engine for approximately 4 to 5 minutes at WOT. If a modification is made which enables the standard load to turn faster, the engine must be making more HP. The last photo shows the electronic tach permanently mounted behind the propeller.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: MJM460 on March 05, 2019, 10:39:22 AM
Hi DRT, thanks for that explanation, its great to know a little of where you fit in.

It is clear that some amazing work is being documented in this thread, and I normally just look on in awe (and silence).  But I am interested in why, when you were talking about identifying those standing wave frequencies in excell, you went to regression analysis instead of the Fast Fourier Transform function.  If it is a big enough data set, and that may of course be the problem, the FFT quickly identifies any natural frequencies in the data set.

Oh, and also, please add my vote to Admiral DK for your build thread on a simpler dynamometer for us mere mortals.

MJM460
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on March 05, 2019, 01:15:38 PM
Hi DRT, thanks for that explanation, its great to know a little of where you fit in.

It is clear that some amazing work is being documented in this thread, and I normally just look on in awe (and silence).  But I am interested in why, when you were talking about identifying those standing wave frequencies in excell, you went to regression analysis instead of the Fast Fourier Transform function.  If it is a big enough data set, and that may of course be the problem, the FFT quickly identifies any natural frequencies in the data set.

Oh, and also, please add my vote to Admiral DK for your build thread on a simpler dynamometer for us mere mortals.

MJM460

I see you're from Australia. Do you know someone named Rod Smith?

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: MJM460 on March 05, 2019, 09:07:05 PM
Hi Jim,

Not that I can recal at the moment.  If he is a model engine maker like yourself, almost certainly not as I dont think I know anyone in that field.

It is always worth asking though, as coincidences do happen.  Was once flying between Toronto and Sarnia, and was asked a similar question.   Turned out I had worked with the guy in Melbourne, and knew him quite well. 

I even worked with a Jim Allen, but that was a very long time ago.

MJM460



Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Zephyrin on March 06, 2019, 07:39:54 AM
Quote
the FFT quickly identifies any natural frequencies in the data set.

You can use Audacity software, that give the frequencies spectrum from the sound track (or noise track...) 
may be helpful when tuning exhaust.
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on March 06, 2019, 06:15:57 PM
The simple fixture shown allows the stock piston bosses to be re-machined to a particular dimension & square to the stock wrist pin axis. What could be the reason that this is being done?

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Admiral_dk on March 06, 2019, 09:45:09 PM
Hmm - since the skirts are further down, it isn't clearance to the crank web ....  I guess reducing weight.
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on March 06, 2019, 11:16:45 PM
Good Guess, but no cigar. There is a part I failed to show which is used to lock up the drive shaft for tightening the 5/16-24 propeller lock nut.

JA
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Admiral_dk on March 07, 2019, 11:17:16 AM
Drilling holes in order to lock the wristpin ?... but wouldn't that weaken it ?

Smart feature, as it will be used every time you need a different prop as load  :ThumbsUp:
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Niels Abildgaard on March 07, 2019, 08:04:37 PM
The simple fixture shown allows the stock piston bosses to be re-machined to a particular dimension & square to the stock wrist pin axis. What could be the reason that this is being done?

Jim Allen

To put piston on a stub in lathe for turning piston top to suit  some far fetched torodial cylinder head
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on March 07, 2019, 09:14:04 PM
Drilling holes in order to lock the wristpin ?... but wouldn't that weaken it ?

Smart feature, as it will be used every time you need a different prop as load  :ThumbsUp:

No. Wrist pins are a press fit in the piston bosses.
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on March 07, 2019, 09:22:07 PM
The simple fixture shown allows the stock piston bosses to be re-machined to a particular dimension & square to the stock wrist pin axis. What could be the reason that this is being done?

Jim Allen

To put piston on a stub in lathe for turning piston top to suit  some far fetched torodial cylinder head

No. Pistons are mounted on an internal expanding collet for final machining. The wrist pin hole & a snug fitting gage pin are used to ensure the piston's OD is square to the wrist pin hole.
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: dieselpilot on March 08, 2019, 02:12:57 PM
Are you shimming between the small end and piston to align the rod between the crankwebs?
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on March 08, 2019, 04:07:56 PM
Correct Dieselpilot!

I will set the total clearance in the upper end at .003" to .005". The total clearance in the bottom end is set at .010" to .015" which means the connecting rod is being guided between the piston bosses. The reason that this works so well is because the rotational speeds in the upper end are much lower than the rotational speeds in the bottom end. I also set the total axial movement of the crankshaft at .004" to .008". There is much more to this procedure that will be explained later.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on March 22, 2019, 08:45:24 PM
This is a custom designed rudder system that allows the rudder actuation to be pulled for right rudder. Standard systems will push the actuation rod for right rudder. All the parts are made of full hard AISI O-1 tool steel. Machined teflon washers & rub plates are used at high wear points. The total movement, right to left, is very smooth & positive with very little friction.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Admiral_dk on March 22, 2019, 10:02:41 PM
The rudder system looks fantastic, but I must admit that I have no clue as to why reversing the movement is such an improvement ....  anything to do with prop rotation  :noidea:
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: lohring on March 23, 2019, 03:23:07 PM
A pull linkage doesn't need to be stiff for accurate rudder positioning.  Since we race clockwise, the boats are making right turns.  Water loads are much higher than most people realize.  Think about sticking your hand in the water in a boat going 20 mph versus sticking it out a car window at the same speed.

Lohring Miller
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Admiral_dk on March 24, 2019, 12:25:35 AM
Thank you for the explanation Lohring  :cheers:  makes sense.
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on March 26, 2019, 04:25:23 PM
I also want to thank Lohring for explaining why this type of mechanism can be used in place of a rod that is pushed for right rudder movements. I must apologize for leaving things unanswered, but I have a large, time consuming, workload. Two other projects that I'm presently working on are shown in the posted photographs. The two 1.500" thick aluminum blocks are the base pieces used to make a die set that will be used to assemble & disassemble three piece crankshafts. Four .500"  OD X 4.500" long dowel pins are pressed into the reamed base holes of .499" ID. These same 4 dowel pins become a slip fit in the movable top piece which has holes reamed at .501". It is very easy making something such as this when the milling machine has been properly trammed. All four holes are drilled & reamed without moving the pre-machined "squared" blocks.

The last photos show how I use a sine vise, with gage blocks, to set up a rudder milling & drilling fixture at an angle. A Sperry AngleStar Digital Protractor is used to check the setting of the angle. This fixture will be used to mill wedge shaped rudder blades.

Jim Allen

Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: DRT on April 03, 2019, 03:51:01 AM
Sorry for the delay You could use a SA, PA, or RTA, and they have those apps on the phones, but I see no particular better reason to record the pipes wave and analyze that way unless you just want to use that method. This was Lohrings method taking point forming a line. Which mathematically I see nothing wrong with. My point is him finding the most accurate line fitting within the method in which he recorded the data. That was the way. This FFT analysis may be a suggestion he could do something with.  I never hear any discussion about 1/4λ or 1/2λ sublimation or constructive interference versus destructive. If a pipe boost similar to a pipe organ I'd expect to see more discussion from that side of things when it comes to a TUNED pipe but I don't want delve deeply here into that discussion only opening a can of worms sourcing my 30 years sound engineering experience. I'll leave that alone here. The only time I even heard the terms use by motor builders was when Jim was telling me about Henry Nelsons magic muffler. So from here it appears Henry was the only one that considered the phenomenon in sound waves with his plane motors.

Don't worry I'm very familiar with recording FFT when analyzing the harmonic content of the electric motors and power systems. I'm a robotics technician for Mercedes Benz.

I'm building a permanent magnet flux switching machine that will produce 25mN from a standstill to nearly no load speeds. @ 2.7kW that's pretty damn good. This design was taken from downhole pump applications. You see the outer rotor has no magnets. The pieces are in the arms of the stator. The motor is only 50 mm in diameter. The motor is also good because it is mostly steel and can give really good performance even with inexpensive steel versus a lot of  expensive rare earth or copper in a high quality conventional pmbldc used for rc models . 

 

Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on April 03, 2019, 05:57:25 PM
Looks like we both have many things going on at the same time Hugh.

I will return to working on the special 1/4", full wedge, 7075-T651 aluminum rudder blades that have a 5/32" water inlet hole. The ID of the entire H2O water line is 5/32" ID without any restrictions up to the engine. This will be the largest water inlet hole ever to be used in a blade of this thickness which has a tapered  back edge towards the bottom. At the point where the side blade H2O inlet is placed the rudder will be .215" thick. This means that both drilled holes must be on center which will give a .0295"/side wall thickness at this point. I use a precision angle block to hold the rudder blank square in two axes for drilling the back edge water  hole. Another fixture, to be shown latter, will hold the rudder blank for the side water hole drilling operation. The same fixture will be used for cutting the rudder's final wedge shape. The water line barbed fitting is a machined brass piece that is pressed into a .2031" ID bored hole.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: DRT on April 03, 2019, 08:41:50 PM
Hi James,

Buzy but can always handle more.....The rudders are beautiful and I want one so send me all the prints for the pieces and lets see how far the "puppy" has come.
 
We're never on any ones time table but G's and he punches the real clocks.... Im going to send you plans for a eddy current dyno similar to the one Lohring started from the University paper I sent you a while back with the hard drive platters with all the acquisition equipment that can handle the speed of you motors. It will be steady state. Realize with the right setup the motor doesn't even have to be hard coupled to the brake. You've seen nothing yet wait till I shake up things injecting ferrofluid in the air gap of my motors for much better cooling and completion of the flux path across the gap. It need no pump James. Because of it curie properties cold fluid displaces the hot fluid that not isn't as magnetic as the cold.  Look up Steve Papell's work at Nasa. he designed it for passive fuel delivery in a rocket engine.

@ Lohring do not share my electric ideas with the electric boaters at OSE or IW they know it all already and I do not want to help any of them at all. You know I'm happy to share them with you if you are interested. In time all of them will see it in Elizabeth City! When I come to claim all my IMPBA jacket speed patches at one time! I'm coming believe me.

Whatever you do, work at it with all your heart, as working for the LORD, not for human masters....
Colossians 3:23 23
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on April 08, 2019, 05:45:24 PM
I have completed the fixture which holds the rudder blank for the 5/32" ID side inlet hole drilling & the side wedge milling. An extra piece will be clamped to the side of the blank when drilling the side water entrance hole. This gives a flat surface for the drill to start into.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on April 11, 2019, 09:40:34 PM
These photos show the new fixture clamped in the vise for drilling the side water entrance slot & milling the rudders wedge shape. The same fixture is used for both operations, only the rudder blank itself is inverted for the side milling operation. The rudder blank is turned end to end for wedge milling of opposite sides. A 5/32" ID hole is the largest hole possible in a 1/4" thickness full wedge rudder.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Admiral_dk on April 12, 2019, 11:49:54 AM
Beautiful rudder Jim  :praise2:

I must admit that there are a few things I can't get my head around here .?

Since I assume that the horisontal hole is pointing forward, it looks like you got the thin part of the rudder profile at the front and the fat part in the back .. This is the exact opposite of what you do to get the optimum flow in air and I would expect that you get "turbulence" at the back => drag .?

Lohring explained why you made your mechanism to make sure you have a pull on the servo (only turning in the same direction) - fine - but I can't help think about why not just move the rudder horn to the opposite side of the rudder - that way you still only get a pull . Is it because the horn then dips into the water when turning or ?

Best wishes

Per
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: lohring on April 12, 2019, 04:41:14 PM
At the speeds model boats run, cavitation and ventilation always happens on the hydrofoils.  The low pressure side of rudders and turn fins drops to the point where air gets pulled down from the surface.  That's even true on the trailing edge of a wedge shape at zero lift.  An airfoil shape is considerably weaker and would still ventilate, giving no drag advantage.  All our foils and propeller blades use wedge shapes.  Without the thickness they would bend.  I personally have bent commercial aluminum rudders like Jim's.

High strength aluminum alloys help, but we ran hardened steel hammer knife blades on our 110 mph boats.  You couldn't run a low drag water pickup in them, though.  We ran a water pickup that was out of the water for the brief timed run.  It submerged during the slow turn around period, cooling the engine. The thin steel blade was good for around a 6 mph speed increase at 100 mph over a thicker aluminum rudder.

Lohring Miller
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: Admiral_dk on April 12, 2019, 07:37:54 PM
Ahh - I forgot about cavitations and it's relevance here  :slap:

Thank you very much for clarifying this for me Lohring  :cheers:
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on April 12, 2019, 08:06:19 PM
Lohring, thanks again for helping with the detailed explanation. I still use a 1/8" thick, hardened & spring tempered AISI-O1 steel, full wedge, rudder on my gas rigger. I use a special designed dual prop blast water pickup that is adjustable in length & depth. Its depth is typically set at 5/8" above the water line at speed & the dual intakes are made of 3/16" ID steel brake lines. This same rudder has been mounted in its custom mount for more than seven years with the same precision machined pivot bushing & its 1/4", drilled out center, dowel pin pivot shaft.

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: lohring on April 13, 2019, 04:01:30 PM
There's an ongoing debate as to whether prop blast water pickups add drag.  The thin rudder has enough lower drag that any drag the blast pickup adds is probably minor in comparison to a thick rudder with an internal pickup.  The decision for us was easy.  We just didn't cool the engine for a few seconds at full power.  If you're trying to set two lap records, this would be a bad idea.  LOL

Lohring Miller
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on April 13, 2019, 08:29:42 PM
I'm sure if the prop blast type pickup is in the water at speed, there must be some loss of speed. I also wonder how much energy & speed is loss as a result of that prop blast hitting any part of the boat as it moves forward considering the 2 ft high 30 ft long spray of water?

Jim Allen
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: lohring on April 14, 2019, 06:05:34 PM
I have no idea how to accurately test the drag of the various water pickups.  I do know that anything submerged has huge drag compared to things in the air.  Water has 800 times the density of air.  Think about sticking your hand out your car window at 60 mph.  Then, if you can find a fast enough boat, imagine putting your hand in the water at that speed.  Don't really try it. 

My favorite bet, and the very rare time I had better intuition than Mike Bontoft, was over streamlining sponson booms.  Even though he built a crude, leaf blower wind tunnel that proved that streamlined sponson booms had much lower drag than the round tubes, I bet that you couldn't tell the difference in an on the water test.  Mike bought me lunch after careful testing couldn't tell the difference at around 100 mph. 

I'm afraid that you would have the same issues with testing the drag of prop blast effects.  As long as you keep submerged things small and to a minimum, you can hang a rag on your radio antenna and I bet it won't matter as long as it doesn't touch the water.  Aerodynamic effects do matter, though.  A careful look at Joerg's 195+ mph hydro below will tell you a lot.  Look at the rear wings that lift everything, especially the water rudder, out at speed and really large fins to hold the boat straight.  Even at almost 200 mph it takes really large aerodynamic fins to equal a tiny water rudder.

Lohring Miller
Title: Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
Post by: strictlybusiness1 on April 17, 2019, 10:23:49 PM
Since I'm  planning on having my wife launch the 17" X 48" carbon fiber cat, it was necessary to mount two very strong aluminum handles. Their mounting areas are reinforced with a carbon fiber plate as well as an aluminum plate. They are mounted at the hulls designed balance point & glued with JB weld.

Jim Allen