Author Topic: miniature 2 stroke gasoline engine  (Read 1467 times)

Offline Old School

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Re: miniature 2 stroke gasoline engine
« Reply #15 on: October 16, 2019, 05:11:34 PM »
 The 40,000 rpm figure is its racing rpm 165 mph, I have not run it under lighter load to see what the maximum rpm is. I don't want to break the engines. The Stelling 2.5cc engines are hard to find and no longer made but still very competitive. They have a steel front housing a heavy cast crank case compared to RC car engines and either drum or Zimmerman induction with a home made pipe.

I have run crowded needle roller big ends in tethered hydroplanes 10cc class they solve the problem of seized big ends, but so does increasing the clearance in the big end.
I also have a 10cc tether car engine with a crowded roller big end mine has never gone particularly fast, but the designers is the second fastest 10cc tether car in the world at around 214 mph, Msts has never told me what his engines rev to

Offline Roger B

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Re: miniature 2 stroke gasoline engine
« Reply #16 on: October 16, 2019, 06:29:58 PM »
Interesting stuff  :ThumbsUp:  :ThumbsUp: I will be following along  :wine1:
Best regards

Roger

Offline lohring

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Re: miniature 2 stroke gasoline engine
« Reply #17 on: October 17, 2019, 03:36:27 PM »
The steel front ends should really help.  It's easier to get good bearing fits when the coefficients of expansion are the same.  Steel is also a lot stiffer than aluminum.  The really fast tether cars should be at the cutting edge of glow engine development.  I'm very interested in the details.

Lohring Miller

Offline Zephyrin

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Re: miniature 2 stroke gasoline engine
« Reply #18 on: October 19, 2019, 02:39:30 PM »
HI,
I have installed the fixing screws between the two cranckase halves, pretty length job but no problem.
it seems to hold well, but it looks fragile, not much material on these legs for screw !
I hope that the tapping will resist upon several assemblies and disassemblies
Reaming (lapping in fact) of the bearings of the two assembled crankcase before the insertion of the bronze bushings to guarantee the concentricity and the proper alignment of both halves.

I have drilled and reamed the bronze bushings held in a collet in the lathe to the final dia (5) then on the same setting, turned their outside dimension, (exactly the same as the bore, 7.11) followed by 5 seconds with Norton microfinishing paper to remove tools marks and facilitate the sliding of the bushings into the aluminium castings.
I still had to force it a little bit with a bolt to get them in, without damaging my castings.

The crankshaft turns between the two crankase halves bolted together without any hard point, phew, not so easy...
I'm happy to have this part done...

https://photos.app.goo.gl/aPDpVnNWrMZHHvAK6

Offline Zephyrin

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Re: miniature 2 stroke gasoline engine
« Reply #19 on: October 24, 2019, 05:47:45 PM »
Today; boring the crankcase for the cylinder, facing of its seating surface and adjusting its height. These tiny castings are hard to hold under the boring head.


Offline Zephyrin

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Re: miniature 2 stroke gasoline engine
« Reply #20 on: October 30, 2019, 11:19:07 AM »
I turned the cylinder in a chunk of cast iron, which was lying around in my garage, not great as a metal.
No particular problem with the machining, but there is a small sealing profile in V on the top of the cylinder that corresponds with a female v on the cylinder head; I put it on, just for fun, because I think it's an unnecessary complication.
The 12 mm bore is then lapped to remove tool marks, up to a nice bore surface, and I get the small extra 0.01mm on the diameter at the bottom of the cylinder, as expected. 

I got confused in the square base of the cylinder; I have to change the position and number of fixing screws, and to make sure that the screw holes do not open into the crankcase!

But at this point of completion, unfortunately, the cylinder fell to the ground, and a fin is broken, it's very ugly, alas.
On reflection, that lasted maybe longer than doing a new cylinder, I'll continue with this one, I'm anxious to see this engine running and I'll do another cylinder if everything goes well…

Offline Admiral_dk

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Re: miniature 2 stroke gasoline engine
« Reply #21 on: October 30, 2019, 10:04:28 PM »
What a shame  :rant:  after all that work and a nice result .....

I hope that the next is without incidents   :cheers:     :popcorn: