Stihl 19cc (20cc) Conversion
 

Some time ago, I converted a Stihl 19.8cc engine for my brother. I believe it came out of a Stihl FS-65 trimmer. We used Gas/Glow. I was impressed with the engine. Light weight, and nice size ports. It ran very well. Finally, my brother came to visit recently, and we got a chance to fly the engine. He put it on a Great Planes Big Stik. With the servos mounted in the tail, the airplane balanced perfectly. We used a 14 x 8 prop, mounted directly to the crankshaft with a large flat washer behind it. There is a chamfer on the crankshaft, and I used a thick washer that I machined the i.d. to a taper to match the chamfer on the crank. The crank threads are left hand, but I figured it might be alright with two nuts jam locking each other, and Loctite. That worked fine on the test stand, for numerous starts and a good bit of running time.

However, when we went to fly it, while checking the tightness of the nuts for the prop, I got overzealous and tightened the jam nut so tight the end of the crank broke off. My brother was anxious to try it anyway, so I Loctited the one nut, and put thick CA on the end of the shaft to stop the nut from coming all the way off, (and the prop), should the prop loosen.

It did come loose a couple of times while we were test running it on the plane, but then I think the prop quit compressing and finally it stayed tight. I don't recommend this idea whatsoever, as the prop certainly can come off and hurt you! But my brother really wanted to test fly the airplane while he was here to visit me, so we did it. I figured I would design a way around the left hand threads later. The crankshaft is small diameter and VERY hard, so options are limited.

Anyway, the test flights went great!! It is a sweet little engine, and perfect for the Big Stick. The airplane took off in about 20 feet without me even pushing it, and flew great at half throttle. It would even do aerobatics with half throttle, and full throttle was a blast. Really a neat little engine, and an excellent combo with the Big Stik.

I sat down and designed a prop hub I thought would work, but then I had the idea, "Why not use a pusher prop and run the engine backwards?" So, that's what I told my brother, and he has some pusher props on order. That should nicely solve the left hand thread problem. There is a pretty good supply of pusher props in the 14 x 8 size from various manufacturers.

I'll let you know when he gets around to flying it again. Here's some pics. I think it would have looked better if he had mounted the engine inverted, but it sure flies great....

Before anyone asks, sorry but I didn't get any tach numbers on the engine.

AV8TOR

RE: Stihl 19cc (20cc) Conversion
 

I have a 16cc Echo engine that came to me without an ignition system, as it had been run with an adapter and glow plug and glow fuel. I would like to run gas/glow in it like you are doing or just methanol. Since, like your Stihl it was originally designed for probably 32:1 or 40:1 gas to oil mix, will straight methanol mixed 32:1 with Klotz Super Techniplate work and be safe for my Echo, with glow plug either lit off just for starting or maybe full time? Will the methanol keep the glow plug lit? If gas is needed for this to work, what percent of gas to the methanol? Is nitromethane or another igniter such as acetone needed?

Thank you very much.

Richard

RE: Stihl 19cc (20cc) Conversion
 

It should run fine on methanol and oil. The methanol is what keeps the glow plug lit, and you will not need full time glow power. The only question is if the carb will flow enough methanol. If it won't go rich enough on the high end, try raising the regulator lever about .020" and see if it will then richen enough. There is a Walbro that is made for methanol use, but it is a bit large for a 16cc engine.

If you haven't already done so, you might read the thread "Gas/Glow How to" found here: http://www.rcuniverse.com/forum/m_80..._1/key_/tm.htm

Good luck,
AV8TOR

RE: Stihl 19cc (20cc) Conversion
 

Hello AV8TOR... What size of pusher prop would I need on my LH 23cc Echo? Sounds like a good Idea...pusher prop for left handed crank threads. Take Care, Capt,n

RE: Stihl 19cc (20cc) Conversion
 

A 15 x 8 to a 17 x 8 or 18 x 6 depending on it's state of tune Captain. I have one Echo 23.6cc that is stock except for running Gas/Glow, free breathing muffler, and an 11 mm carb. I run an old wide blade Top Flite 18 x 6 on that one. It turns that prop at 7500 and hauls the big Great Planes Fokker Triplane around really nice.

Then I have a fully hopped up Echo 23.6 on a 72" span Katana. I run an APC 16 x 8 on that. Turns over 9000 and flies well too. Depends on the plane and what you want, as you know.

AV8TOR

RE: Stihl 19cc (20cc) Conversion
 

Just thought I should add a note here about using pusher props on a tractor airplane and running the engine "backwards"... Be prepared for using LEFT rudder instead of right rudder in high power-low airspeed flight conditons such as take off and climb outs.

Tractor configuration ultralight airplanes with gear box reduction units, and some full size airplanes from Europe are this way as well.

AV8TOR