Building a VW Aero-Engine

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simflyer

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..... Some people says they have trouble with the bolt-on 87mm cylinders and pistons for the 1700 engine, but I never did.
1700cc engine uses 88mm cylinders and as You wrote, it shouldn't be problematic, with normal compression.
1835cc engine with 92mm cylinders needs to resize cylinder holes in block too big, so bolts are too close - haven't enough material around bolt and with higher compression are bolts often pulled out of block.
 

Flyguyeddy

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1700cc engine uses 88mm cylinders and as You wrote, it shouldn't be problematic, with normal compression.
1835cc engine with 92mm cylinders needs to resize cylinder holes in block too big, so bolts are too close - haven't enough material around bolt and with higher compression are bolts often pulled out of block.
You do know that there is such a thing as 94mm cylinders, that are also quite common?
 

simflyer

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I didn't heard around about use of 94mm bore, or even common. Also think, that bore over 92mm is nonsense on VW type I and it only produces problems. Simpliest tuning, without need of machining block and heads, is use of 74mm crank and 88mm bore cylinders - it gives 1800cc. Next cubatures in table, but cranks also exist with 76mm.
 

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Vigilant1

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Pops,
In a previous post ( this thread) you quoted Hot Wings and wrote:
It's about power and reliability.

The thin wall 92s don't make as much power as the 90.5s and the 94s don't make as much as the thick wall 92s. The thin walls just distort too much over time.
Weld and fill in the area at the flywheel end of the case behind #3 cylinder, bore for 94 mm pistons and jugs and then use the heavy wall 92 mm pistons and jugs.
From this, I gather that in your experience the heavy wall 92mm pistons are worth any possible issues with the thinner case due to the required 94mm machining of the case. Have I got that right?
 
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Vigilant1

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I didn't heard around about use of 94mm bore, or even common. Also think, that bore over 92mm is nonsense on VW type I and it only produces problems. Simpliest tuning, without need of machining block and heads, is use of 74mm crank and 88mm bore cylinders - it gives 1800cc. Next cubatures in table, but cranks also exist with 76mm.
I think most (not all) VW aero engine builders agree, based on a lot of experience and a lot of off-airport forced landings, that going above 69mm stroke requires that a beefier bearing be used if we are driving the prop from the pulley end of the case. That means more expense to buy the Force One bearing and hub, and it requires machining of the case. Even without that, a 74mm crank will require case clearancing unless special rods are used. And going with a 74mm or 76mm crank will increase piston speeds and stresses compared to the same RPM with a 69mm crank.

The potential advantage of the 74mm stroke 1800cc engine might be greater HP at lower RPM than with a 69mm stroke 1835cc engine. So better prop efficiency from a longer prop. I'd say the jury is still out on that. Also some planes can't use a bigger prop due to clearance issues.

So, lower initial cost, lower complexity, higher HP, and (potentially) better reliability would be the reasons I see for favoring a 69 stroke/92 bore 1835cc engine over a 74 stoke/88 bore 1800 cc engine. I think the comparatively larger number of 1835cc vs 1800cc VW airplane engines indicates there's general agreement on these points. Right? Wrong?

Edited to add: Are appropriate pistons for 74mm stroke widely available? Expensive? From what I recall, the widely available pistons are for either 78-82mm stroke and for 69mm stroke.
 
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Flyguyeddy

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Pops,
In a previous post ( this thread) you quoted Hot Wings and wrote:


From this, I gather that in your experience the heavy wall 92mm pistons are worth any possible issues with the thinner case due to the required 94mm machining of the case. Have I got that right?
You can get cylinders that have a 92 base and a 94 top
 

Flyguyeddy

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I didn't heard around about use of 94mm bore, or even common. Also think, that bore over 92mm is nonsense on VW type I and it only produces problems. Simpliest tuning, without need of machining block and heads, is use of 74mm crank and 88mm bore cylinders - it gives 1800cc. Next cubatures in table, but cranks also exist with 76mm.
I guess revmaster and aerovee have never heard that. You better call em up
 

Pops

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I think for the money, HP and reliability the 1835cc, 60 hp is hard to beat.
The 1835 in the SSSC with the 60"x 26" pitch prop had the same performance as a friends Sky-Rader that had the same span, wing area, same EW and both airplane had the same ROC, cruise speed, take-off distance. The Sky-Rader had the 60 HP HKS that uses a prop reduction. VW is straight drive.
 

Vigilant1

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Do you know how thin the bottom of the 88mm slip in cylinders are? They are mighty thin.
Yes. They weren't (aren't?) universally loved. Post
Way back in the early days of slip in 88s* we started paying those costs.

* total junk BTW. 87's weren't much better.
That's why I'm asking about the 94mm cylinders.
 
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flitzerpilot

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The prototype Flitzer Z-1 is equipped with an 1834cc VW and presently turns a 60" x 34" (root) 32" tip propeller which restricts rpm to 3000. This still delivers a RoC of around 600 fpm and a cruise of 85 mph: max level speed is 92 mph. However it has a low tare weight of 480 lbs. 'Vintage' biplane drag being what it is, I think this demonstrates a good performance with this reasonably priced engine.
 

Flyguyeddy

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There was a gentleman who built a flywheel drive 2332 (same as revmaster sized engine) and ran it on a sonerai for several hours. He reported no issues and eventually sold ghe engine to someone else who also, last reported, didnt have any issues either.
Large engines can be built to be reliable, but id imagine they would be better suited for faster airplanes

“special rods” is a moot point on these engines as youre gonna be buying new rods and parts anyway, mught as well get those fancy 5/16 arp bolted rods that make stroker clearance issues less of an issue.
 

Pops

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The prototype Flitzer Z-1 is equipped with an 1834cc VW and presently turns a 60" x 34" (root) 32" tip propeller which restricts rpm to 3000. This still delivers a RoC of around 600 fpm and a cruise of 85 mph: max level speed is 92 mph. However it has a low tare weight of 480 lbs. 'Vintage' biplane drag being what it is, I think this demonstrates a good performance with this reasonably priced engine.
I believe if you went to less pitch you will get more climb with the same top speed.
 

Hot Wings

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Bet Hot Wings has something better.
Nope.
When I built VWs for pay I had a shop in Denver that did my rods in bulk. They matched the sets for me. Since then I farm out this kind of work to a local shop that specializes in balancing.
When I needed to DIY I cobbled something together using my chemistry lab equipment.

Will have to enlarge ID of the shims .050 " to slide over the #1 bearing surface of the crank
It has been a few years and my memory isn't 100% today but I seem to remember that the older gasket style flywheel/crank used larger ID shims and I had a selection of both sizes on the pegboard at the rebuild station?
 

Flyguyeddy

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Opening the middle bore of the shims would be super simple in a lathe with a tool to hold them. Just do a big stack of them all at once held in an OD fixture that clamps them in place
 

Hot Wings

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Do you know how thin the bottom of the 88mm slip in cylinders are? They are mighty thin.
He may have been thinking about cut case/head 88s? Slip in 88s were notoriously short lived. In the early days of big bore VWs, at least 2 versions of 88s that needed machine work existed. One version used standard 92 cylinder dimensions and another used a slightly smaller hole.

I have to defer to Pops for aviation use as he has FAR more experience there than I do but I've never seen a problem with the studs pulling on a case cut for 92s that didn't have some other contributing factor - like detonation or overheating - on ground bound VWs.
 

Flyguyeddy

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He may have been thinking about cut case/head 88s? Slip in 88s were notoriously short lived. In the early days of big bore VWs, at least 2 versions of 88s that needed machine work existed. One version used standard 92 cylinder dimensions and another used a slightly smaller hole.

I have to defer to Pops for aviation use as he has FAR more experience there than I do but I've never seen a problem with the studs pulling on a case cut for 92s that didn't have some other contributing factor - like detonation or overheating - on ground bound VWs.
Agreed.
Also, bob hoover himself promoted a 94x84 engine as an ideal build for homebuilts, after the fat fin mod was done
 
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