Author Topic: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine  (Read 88342 times)

Offline Stuart

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #30 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

My aim is for a accurate part with a good finish

Offline JMcRae

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #31 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.

Offline Niels Abildgaard

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #32 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.

Offline Admiral_dk

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #33 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

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #34 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
« Last Edit: August 22, 2014, 01:05:03 AM by strictlybusiness1 »

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #35 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
« Last Edit: July 19, 2014, 10:02:59 PM by strictlybusiness1 »

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #36 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

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #37 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
« Last Edit: October 20, 2014, 08:24:28 PM by strictlybusiness1 »

Offline Niels Abildgaard

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #38 on: July 20, 2014, 04:01:38 PM »
A picture of a Bugl drum inlet



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

kind regards

niels
« Last Edit: July 20, 2014, 04:57:02 PM by Niels Abildgaard »

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #39 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

Offline Admiral_dk

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #40 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

Offline dieselpilot

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #41 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

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #42 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

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #43 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

Offline JMcRae

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #44 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.