Author Topic: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine  (Read 80610 times)

Offline strictlybusiness1

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.90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« 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
« Last Edit: July 18, 2014, 12:17:56 PM by strictlybusiness1 »

Offline ths

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #1 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.

Offline Niels Abildgaard

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #2 on: July 18, 2014, 03:59:03 PM »
Hello Jim
More music please.
What kind of beer can I bring You?

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #3 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


 
« Last Edit: July 18, 2014, 04:30:37 PM by strictlybusiness1 »

Offline JMcRae

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #4 on: July 18, 2014, 04:52:31 PM »
Beautful work! may I ask what the connecting rod is made of?

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #5 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

Offline Roger B

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #6 on: July 18, 2014, 05:31:50 PM »
Gosh  :o  Interesting stuff  :ThumbsUp:  :ThumbsUp:
Best regards

Roger

Offline JMcRae

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #7 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.

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #8 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

« Last Edit: July 18, 2014, 07:13:39 PM by strictlybusiness1 »

Offline Marinus

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #9 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?
Kind regards

Marinus Kruger

Offline JMcRae

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #10 on: July 18, 2014, 07:31:07 PM »
How fast is the record you set Jim?

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #11 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
« Last Edit: July 20, 2014, 11:50:58 AM by strictlybusiness1 »

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #12 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


Offline JMcRae

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #13 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?

Offline rockknocker

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #14 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?