1/2 VW - 2-Cylinder Aero Engine

[GreenTwin]

We got off-topic in another scale 4-cylinder VW engine build, and started talking about 1/2 2-cylinder VW engines.

I am starting this thread so as to not hijack the original VW 4-cylinder thread.

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[GreenTwin]

There was a show on TV about someone who was in some sort of ultralight competition, and he uses a 1/2 VW engine.
He had problems with it, and could not get it to perform correctly.
I think the fundamentals of a 1/2 VW design are ok, assuming you did your design homework, and could get the crankshaft and timing worked out for a semi-smooth run.
There are many twin designs like that which run well, such as the BMW motorcycle engine, so obviously it can work well.

I noticed a lot of TIG welding on the head.
I would cast a new head and crankcase, and perhaps cast a new crankshaft in ductile iron.
Lost PLA on the cylinders and heads.

I would make it at least 1/2 size, but I guess we better save that discussion for a new thread.

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[GreenTwin]

Tom-AMS posted the following, which brings up many questions.

My company has specialized in both air-cooled VW & Harley engine rebuilding since 1963, we've built many engines for aviation and or industrial applications. (plaines, gen sets, air compressors, natural gas compressors. IIRC, Global Machine Tool sold a 2 cyl VW for aero use; I think Mosler, Inc bought out Global. Others were Hummel Engines, Better Half Engines, Simplex. One unique 1/2 VW engine put out by Lonestar Ultra-Light used the VW crankcase/lower end with Harley TwinCam cylinders and heads. The "all VW" 2 cyl are good for ~40 hp, while the "HD/VW" makes ~73 hp. Cutting and welding the VW vase is not as difficult as it may seem. I did my first one in 1969 - the mag alloy is either AS41 (later cases) or AS26 - both TIG weld easier than welding aluminum, from my experience. There are also aluminum alloy cases (we sell both new alum. & mag cases) however the aluminum case weight about 14 lbs more than the mag alloy case... so not the best choice for aero.
Tom-AMS

How are you getting 40 hp out of two cylinders ?
Better air flow, better carbs, better compression ?
That is a bit of a trick.
Does the engine life have to be derated ?

What about a thrust bearing ?
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[GreenTwin]

ddmckee54 posted these from the other thread.​

I am going to copy these here for the purpose of discussion.
Photos by ddmckee54:

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[NapierDeltic]

Do not forget Citroën had a large family of Twins - air cooled simple engines:
https://citroenvie.com/2cv-engine-praise/

 

[GreenTwin]

Do not forget Citroën had a large family of Twins - air cooled simple engines:
https://citroenvie.com/2cv-engine-praise/

View attachment 165670

That is a cool little engine.
I don't recall ever seeing a Citroen here growing up, and so I never became familiar with that car or engine.

There were many VW's of various types, and I had several of those, but never had a microbus, but I wanted on until I test drove one.
It was like floating on a cloud, since you were up over the front wheels. Did not feel stable at all, so I did not buy it.

Ditto for an old army Jeep.
I drove it, and it had this floating type feel to it.

I bought a Fiat 500 from the junk yard, just to take apart and play around with.
I remember the small engine in the back, but can't remember how many cylinders.
Seems like it was water cooled.

Thanks for posting that info.
Very nice little engine !

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[Tom-AMS]

Tom-AMS posted the following, which brings up many questions.

My company has specialized in both air-cooled VW & Harley engine rebuilding since 1963, we've built many engines for aviation and or industrial applications. (plaines, gen sets, air compressors, natural gas compressors. IIRC, Global Machine Tool sold a 2 cyl VW for aero use; I think Mosler, Inc bought out Global. Others were Hummel Engines, Better Half Engines, Simplex. One unique 1/2 VW engine put out by Lonestar Ultra-Light used the VW crankcase/lower end with Harley TwinCam cylinders and heads. The "all VW" 2 cyl are good for ~40 hp, while the "HD/VW" makes ~73 hp. Cutting and welding the VW vase is not as difficult as it may seem. I did my first one in 1969 - the mag alloy is either AS41 (later cases) or AS26 - both TIG weld easier than welding aluminum, from my experience. There are also aluminum alloy cases (we sell both new alum. & mag cases) however the aluminum case weight about 14 lbs more than the mag alloy case... so not the best choice for aero.
Tom-AMS

How are you getting 40 hp out of two cylinders ?
Better air flow, better carbs, better compression ?
That is a bit of a trick.
Does the engine life have to be derated ?

What about a thrust bearing ?
.

Thust bearing(s) are easy: for both the 4 cyl & 2 cyl engine we use the same double flanged thrust #1 main brg, at the flywheel end. and we replace the original #3 full-circle main located begind the timing gear, with a modified flanged #1 main brg. We simply machine away one of the original thrust brg's flanges, side-cheek the crank so it's smooth, then measure the distance on the crank from thrust surface. Use this and a little math to allow for the brg flanges & endplay to face an appropriately spaced counterbore for the single inboard flange of the new #3 main. The crank is "sandwiched" between the inner flanges of the two brgs. Easy to and VERY much stronger, reliable than just the original thrust brg set up.
Power gains, for our engines, come from improved porting & valve flow, cam profiles, big bore P&L, compression chamber quench mods, and the use of two types of internal engine part coatings. We primarily seek to increase Torque over rpm, so HP gains are modest compared to what we achieve for other engines apps

 

[Tom-AMS]

these are 2 & 4 cylinder VW-engine based pumps we manufacture for compressing natural gas, at well sites. most are powered by electric motors. Some have roots-type blowers, Others are self-powered using two of the four cyls,. And some are powered by 3 or 4 cyl Kubota engines. All but the self -powered models have crankcases pressurized with 3~5psi natural gas. All versions are converted to 20 to 25 gallon dry-sump oiling systems. They typically ran 24/7/365 for ~ 3 yrs. before being called back in for overhaul.