# Steps to scratch build a VW

Discussion in 'Hangar Flying' started by Little Scrapper, Aug 13, 2019.

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1. Aug 14, 2019

### Pops

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Yes I think you are correct, 1600 cc's .
On the sonerai site someone went from a 2180 cc engine to a 1835 cc engine and lighten up the airframe and liked the airplane a lot better. Everything else being equal going to the 2180 is just costing you 2 pounds increase in engine weight. Stroker crank is heaver but the pistons are lighter for the stroker crank over the 69 mm stock crank.

2. Aug 14, 2019

### Pops

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http://www.greatplainsas.com/scphub.html

The Aero-Vee prop hub is sort of a copy of the Force one but with less surface area and a shunk fit with the taper fit of the Force One. Never been a failure of the Force One but there has been failures of the Aero-Vee prop hub.
Which is better? , lot of people have different opinions. My self I like the Force One.
If I was to build another 1835 cc engine, I think I would just go with the Force One for the extra insurance over the Shunk fit prop hub. Talked to Steve about this one time and he said it was over kill, but I like over kill when flying.

https://onex-svingenb.blogspot.com/p/propeller-hubs.html

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3. Aug 14, 2019

### dmar836

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I have never had a Force One hub but have studied it a bit. The nose of the engine case is machined for an additional bearing that rides on the inserted hub once it is pressed onto the crank.
Hoover and others have discussed the failure mode of the stock crank(and presumably a new crank of the same dimensions) in aircraft to be at the pulley keyway spiraling back to the #4 main. I can only assume the additional support ahead of that point, with the added bearing, prevents gyroscopic forces from taxing the crank there.
The stock VW crank is supposed to be a great piece unless abused. We use them at lower rpms than even the factory recommendations. If I had one in good shape(and I do) I would use it with the F1 hub. As is, my build is driven from the opposite end.
I’ll add, the older I get and the more I have learned from my mistakes, magnaflux is cheap assurance when deciding on parts.
Dave

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4. Aug 14, 2019

### Vigilant1

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If I've got this right, the main difference between the Force 1 and the shrink-fit prop hubs is that the Force 1 unit contains an entirely separate bearing that is much larger than the stock bearing on that end of the VW crankshaft. This is why using the Force 1 requires machine shop work--the case has to bored at that end to make room for the Force 1. From the GPAS site:
That bit about the crankshaft nose is also important, as, when crankshaft failures occur, a typical spot is right where a shrink-fit prop hub ends, due to the weakness caused by the slot for the Woodruff key and the tapped hole in the end of the crankshaft. The stock crankshaft and bearing on that end was designed only to carry the load of a small pulley, not a
wooden propeller with its gyroscopic loads.

Revmaster also beefs up that bearing, they use something that's not quite the same as the Force 1, but accomplishes the same thing: More radial load capacity.

Along with the Force 1 hub, GPAS also sells their "Top Bug" crankshaft, which has an excellent reputation.

In general, I think there's agreement that, with a qulaity crankshaft, engines with the standard 69mm stroke can safely use a shrink-fit hub and there's no need for a beefed-up bearing (so, 1915cc max displacement (94mm bore), but 1835cc (92mm bore) is more common). But, the Force 1 doesn't hurt, and it is relatively cheap insurance. Sonex believes that their Aerovee 2180cc engine is fine with the stock bearing and the shrink-fit hub, and many thousands of hours have been successfully put on that type of setup, it does save some money. FWIW, the builder of my Sonex put an Aerovee engine in, but later installed a Force 1 hub, and I'm happy he did that.

One of the keys to the evolution of dependable VW aircraft engines was the hard-won knowledge about cranks and bearings. It's important to make use of the knowledge gained over a lot of years.

All the above is subject to correction by folks who know more (which is a lot of folks!)

Last edited: Aug 14, 2019
5. Aug 14, 2019

### Hot Wings

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It transfers the torque to the prop flange via a tapered fitting - far superior to a shrink fit.

It also transfers the bearing surface for the front bearing directly to the prop hub. It's still a weak place on the case to transfer gyro loads, but it's about as good as can be done without a purpose built, or welded case.

If you only want to build something like a Dormoy Bathtub the shrink fit is probably going to be OK.

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6. Aug 14, 2019

### Pops

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I think the SSSC is coming up on 300 hrs and its been as dependable as a Cont A-65 . Has the GP's shrunk on prop hub and Zenith carb, Slick mag and single port heads. I always wished I had went to the Force One prop hub on the engine, but zero problems with the Shrunk on hub. The Zenith 60" x 26" wood prop weights 3 lbs. Steve said that prop on the Shrunk on hub would be OK and not worry about it. So far he has been correct.
I used a stock (69mm) like new German crank that I was saving for an aero-VW engine.

I also like GP's "Top Bug" crank. Looks like they took care of all the weak points.

Last edited: Aug 14, 2019
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7. Aug 14, 2019

### Pops

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Everyone has really posted some good points about the VW.
Thanks.

8. Aug 14, 2019

### Vigilant1

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This may be useful to some folks:

In the past, the Great Plains catalog has been a tremendous resource for those learning about VW engines. While it wasn't a textbook or a builder's manual, it was more than just a listing of what GPAS sold. Various sections sometimes gave history on the development of some parts and it was also possible to see the choices a builder might have (flywheel end or pulley-end prop? Magneto ignition or electronic? etc).

The GPAS catalog has been getting more "streamlined" over the recent years, and it now appears to be gone altogether from the GPAS web site (though the descriptions of the individual parts appear to be screenshots of sections of the old catalog). I'm sure GPAS has taken this step because it was difficult to keep the old catalog up to date, and this new approach is easier.

Attached is a copy of the GPAS catalog I downloaded in 2011. It contains some of the distilled wisdom Steve Bennett accumulated over decades of his time in building VW airplane engines and running a great business that remains a key part of the homebuilt airplane community. Lots of good stuff here. Obviously, this is for information use only--the prices are all out of date and I'm sure many of the items shown are no longer for sale.

It's a big file PDF file, about 7.5 MB. You won't want to read it on your phone.

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9. Aug 14, 2019

### Turd Ferguson

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So many of those John Muir books were published there is probably one book for every VW that was ever on the road.

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10. Aug 14, 2019

### rickofudall

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Another book you might want to pick up is HP Books, "How to Hot Rod Volkswagen Engines". The book is ancient, I got my first copy in 1971, but all the information is useful. The last engine I built was a very balanced 1600 for a bus. I could run all day at 65 with two hang gliders on the roof and my retrieve bike inside it got 25 mpg.

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11. Aug 14, 2019

### rickofudall

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Forgot something. Don't know if it's applicable anymore but from VW there were hi and low piston sets. Both would have a 5 gram variation in piston weights. The local VW dealer in Bellingham, WA let me spend a couple of hours going through piston sets to mix and match until I had a set within 2 grams. This was a common practice of Formula V builders and the dealership liked to display the owner's race car so he was very nice to engine builders. Anyway from there I got out my triple beam balance and Dremel and ended up with four pistons within .25 grams. That and balanced rods made for a very smooth engine.

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12. Aug 15, 2019

### Pops

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Balancing a VW makes a big difference.

13. Aug 15, 2019

### lakeracer69

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1) I've been seriously considering a flywheel forward engine for my Lil Bitts. Does anyone have any pictures of the parts and hardware necessary to drive a magneto and alternator off of the pulley end of the motor? Motors turned the other way can use that Diehl mount, like a Sonerai.

2) Any pictures of cases with the case tops and bottoms machined down for cowl clearance when running flywheel forward? This has been something I haven't been able to find any pictures of. It has the potential to weaken the case if done excessively. Maybe the pylon racing guys have do it.

3) Are there machinist drawings of what work has to be done to a crank and case to accommodate the Force one prop hub? It would be nice to know for someone who wants to put the prop on that end. I'd like to look at exactly what they have done.

14. Aug 15, 2019

### Pops

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Chad Stenson on the Sonerai site used a flywheel drive and cut the VW bellhousing flange off.
No one makes a mag mount for the pulley end of the engine. I have designed one and have some of the parts made for my flywheel drive engine.

Picture of Chad's engine in his Sonerai.

http://www.sonerai.net/articles/aerocarb_tips.pdf

15. Aug 15, 2019

### 103

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Robin Taylor sells her father inlaws book for a very reasonable price. http://vikingaircraft.com/photos/

Rex is a good Man. I enjoyed speaking to him in the late 80's.

Last edited: Aug 15, 2019
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16. Aug 15, 2019

### Little Scrapper

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Good questions. I find it odd there's not information on this too, I looked and and couldn't find anything.

I'd like to find out how Steve Wittman set up his motor.

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17. Aug 15, 2019

### TFF

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Remember Wittman had actually less to work with and he was constrained by racing rules. He also had the drive extension, and if it’s like his V8, the housing carries bearings and a stand in airplane crank prop end. The V8 one had a tapered Continental crank end. I can see him at putting a A-65 crank prop end on it. Do the plans have that info or was that separate info you had to get from him?

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18. Aug 15, 2019

### dmar836

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Articles about Wittmans formula V build(V-Witt) state he used a C-65 prop hub. Not sure if that is true or talk. The scan of his plans show a 4140 hub of his own dimensions. That’s a big chunk of chromoly for the shaft and another for the hub. I found a chunk and made a prop hub to fit the shaft that came with my project. The C-65 hub was huge in comparison. I made my hub with the “VW pattern”. It’s also a tapered fit.
I have thought about it but have not heard of many removing the transmission flange from the block and this is only useful if one wants that #1 main bearing out front. This adds more  and work than just going with the F1 hub IMO as you still need a prop extension and hub plus a mount and coupler for a mag. To me adding, say, even a 4” prop extension to the stronger flywheel flange end of the crank with that larger bearing, would add forces that put us back at the initial problem. Maybe not with The woodruff key area weakness but with gyro forces to a crank not designed for that. Not done too often so I wouldn’t want to start the learning curve on that setup. It’s taken a long time and many failures to learn ourselves into a reliable hub setup. Remember Wittmans had a long extension but supported it with a carrier bearing at the end in a cast cone(a frustum actually). I’ve heard he dealt with harmonics and I’m not looking forward to that.
My mag mount for the “Wittman direction” engine was a cobbled together series of spacers and washers with a few angled brackets from elsewhere on the block. They held two plates that mounted the mag and a special modified crank nose pulley with a phenolic coupler. All quite crude and will be redone. I’d be interested to see what Pops came up with.
Many build with twin plugs and mags, battery(or multiples), starter, tuned exhaust with mufflers, etc. When weight is mentioned everyone sites safety. I get it but at some point I would be tempted to just drop in a stripped down C-65.
Dave

Last edited: Aug 15, 2019
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19. Aug 15, 2019

### Pops

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When VW were first used for airplanes putting the prop on the flywheel end was the normal way. When putting the prop on the pulley end become the normal way when the VolksPlane article came out one the front cover of a magazine. At that time the 36 and 40 hp was used and the shrunk on and tapered prop hub on the pulley end was no problem. When going to the larger hp engine when the problems started.
I'm using Bob Hoover's plans for the prop hub on the flywheel end of the engine. It's 4" long. Also going to trim about 1/2 of the bell-housing off of that end of the engine. Bought the chunk of 6061-T6 aluminum on E-bay for \$40.
Bob's engine mount ---https://bobhooversblog.blogspot.com/2009_02_06_archive.html I'm making the same bed mount but longer in height to fit the firewall of a SSSC.

I have never heard of a crank failure when using the flywheel end to drive the prop. Don't think Steve ever heard of one.
Picture of the center turned out of a flywheel to mount the prop flange.

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20. Aug 15, 2019

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