# Aircraft VW reliability - What have we learned?

Discussion in 'General Experimental Aviation Questions' started by Little Scrapper, Dec 22, 2016.

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1. Dec 24, 2016

### Pops

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In post #52, it was mentioned about "Fat Fin Heads". That was Wayne Clagg, friend of mine that lives about 40 miles south. He put a large VW engine in his Zenith 701 with the belt drive. With all the bells and whistles on the engine, he told me that the engine weighed 235 lbs, if I remember correctly. Had heating problems from running the engine so hard. I think he said the cruise rpm was 3800. When he would fly up to my field, it almost sounded like a hi-rev Rotex. He was on his way to OSH in the 701 with about 80 hrs on the engine and the engine case cracked. Trucked it home and put a R-912 in it.
The added fins that he welded on did help some, but no enough for the HP that he was demanding from the engine.

2. Dec 24, 2016

### Vigilant1

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Pops,. If I recall correctly, Bob Hoover thought the "fat fins" were a pretty big deal, and he'd tested them and believed they would give the VW some increased utility at the upper HP range that we sometimes ask of them. The breakthrough was some type of newly available welding rod that permitted good weld to the AL fins. Seemed reasonable, but I don't know if many folks have done it or if they have documented their results.

3. Dec 24, 2016

### Pops

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Yes, Increasing the fin area does help, but as Wayne found out the fin area needs a large increase. He did use the welding rod for aluminum that is done with a gas torch as in brazing. Even a good cleaning of the metal flashing in the air passages in the heads with round files helps. VW engine builders making sure the air passages are as clean as possible is a normal part of building a VW aircooled engine. I have seen heads where some of the air passages was completely closed.

There is a lot of poor quality VW parts on the market. One time I bought a oil pump cover plate with the outlets for a oil filter and cooler. The surface had a .010 warp between bolt holes. The stock gasket is .004 thick, so there was a .006 gap for the oil to leak. Junk part. That is why buying parts from someone like GP's is important. All the junk parts are filtered out.

4. Dec 24, 2016

### wanttobuild

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Scat Split Port Head
Ben

5. Dec 24, 2016

### BobbyZ

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I feel the same way.The architecture is well proven and by using the larger V8 journals it opens up a lot of options for high quality well designed bearings.That are capable of handling the sustained loads of a aircraft engine.

Pauter has squeezed a relatively reliable (as far as high HP 4cyl racing engines go)900-1000HP from these things.There's no doubt in my mind that says we couldnt get a reliable 100-115hp motor (if not more) from their block.The problem is it's expensive and they also have no interest in aircraft conversions whatsoever.The guy I spoke to there even said they could easily adapt the design so that it could run a standard Lycoming front bearing because of everything being billet and chances are they could even stretch it to 6 cylinders if they wanted to.But he said it'll never happen and he really wasnt supposed to speak about A/C related engines at all.On a second call I received a "I'm sorry we dont deal with them" and they hung up.

I dont know if their design is under patent or not.But with todays CNC machines the reality of someone doing such a thing is within reach of a lot more people now than it was just 5-10 years ago and the crankshaft is the hardest thing to machine but even so there's plenty of companies who can do them for a reasonable cost and make you rods to boot.

With a custom block and billet crank you could adapt a aircraft front bearing and hub pattern,use top shelf bearings for the rest of the engine that were designed for more load and the end result would be impressive
Besides the crankshaft and block pretty much everything else will be off the shelf aftermarket parts catalog components.Also you could forgo the custom made parts and use their block but at that point I dont feel it's worth it.Plus I think it could be made for less and improved for aircraft use at the same time.

The problem is it wont be cheap and that is what I feel is the VW's point.It's a affordable engine that is perfect in 40-60 hp applications like Pops plane and the glider before that.Plus you can easily add stronger modern parts to make it bulletproof when you build it.It's almost cheaper to buy a decent set of aftermarket rods then it is to resize a stock set with new bolts
But with the right person behind it they might be able to find a niche for a lighter engine based off the VW around 3L & 100-125 hp.But I just can't see the price coming in under 20$grand let alone being close to what a Revmaster etc sells for.At that point a certified engine would most likely be less.Someone would have to make quite a investment to produce a bunch of them in order to reduce the price to a point where it began to make sense and that just isnt going to happen. But if someone had a extra$30+ grand and was determined to push a VW past where they are now,its a possibility :gig:

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6. Dec 24, 2016

### TFF

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Lycoming and Continental naturally aspirated engines usually make 1 HP per 2 cubic inches. With the same ratio a 1835 should not be pushed more than 55 HP,a 2100 64 HP, and 1600 at 48 HP. If you are needing 80 hp continuous out of a VW you are pushing the engine well outside convention. Same with aircooled and watercooled motorcycles. 1000 hp drag VWs dont run 15 seconds from start to finish and only run 6 seconds at full power. Top Fuel engines are "air cooled" at 4000 hp. There are no water jackets in them.

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7. Dec 24, 2016

### BBerson

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Yeah, it will only make about 1hp per two cubic inches at 2700rpm no matter how many racing parts are installed. (normal fuel, no turbo)
The racing engine will be much heavier with such things as counterweighted crank, which isn't needed at 2700 rpm.

8. Dec 24, 2016

### Turd Ferguson

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There is always the Limbach VW derivative that is reliable enough to be type certificated. I'd take one of those engines in a blink!

9. Dec 24, 2016

### BobbyZ

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A billet crank can be cut anyway you like So if you'd rather delete the counter weights it's only a little more than a click away.

As for the aftermarket rods,yes stock rods would be fine but when you can have a better set for what it costs to rebuild the stock ones.It's kind of pointless to bother with them.

10. Dec 24, 2016

### lake_harley

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TFF, with those couple sentences, I think you've hit the nail on the head! It's always seemed to me that "real" aircraft engines are built to be durable first, and then big enough, displacement-wise, to make the HP required. An old adage in racing is "there's no replacement for displacement". Increases in HP output without changing displacement usually comes as a result of changes (I won't even call them modifications) that produce HP through increasing RPM (ie: cam profile), and or things that add more stress to the engine's components (ie: increased compression ratio). In my novice view aircraft engines need neither of the above.....high RPM or highly stressed parts.

Opinion worth price paid.....\$0.00

Lynn

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11. Dec 24, 2016

### Little Scrapper

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The mystery I see is people having an engine out and nobody knows why. Maybe I'm just paranoid of the VW, and some of this is in my head. I do know that there's an absolute abundance of VW people who post on forums trying to get the VW running correctly. When I say forums I'm mean aircraft specific forums like sonex, sonerai etc.

12. Dec 24, 2016

### BBerson

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The stock forged crankshaft is adequate.

13. Dec 24, 2016

### Topaz

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It would only be a meaningful observation if Lycomings, Continentals, etc. were non-certified, sold by a dozen vendors, and everybody had to put them together themselves, in which case you'd see the same thing for them.

The VW is not a certified engine. There is no "standard", there is no supervision by the FAA or anyone else. Other than the kits put out by Great Plains, Casler, Revmaster, AeroVee, and the like, there isn't even a "agreed-upon way to convert a VW into an airplane engine." If you don't buy a kit or plans from one of those "established" converters, you're on your own to do exactly whatever you want, however good or dumb that might be.

Given those conditions, of course you're going to have people asking questions and having issues. If it's people asking questions of AeroVee motors, the Sonex forums would be the place for it, given that Sonex and AeroVee are the same company, for all intents and purposes.

'Scrapper, honestly? You're level of discomfort here goes way beyond "usual". Dunno why that is, and I don't know you well enough to call you "paranoid", but the VW conversions, like the Corvair conversions (which share the same plusses and problems in terms of being a non-certified, experimental engine), have a long history of pulling airplanes through the sky. Small and light airplanes in the case of the VW, to be sure, but a long history nonetheless. Until Corvair came along to meet the need for more power, VW's were pretty much the "auto conversion" engine for airplanes. Over the decades, probably more of them have flown in homebuilts than all other aero-conversion types put together.

If there were some fundamental problem with the idea of converting a VW to airplane use, we'd know of it by now.

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14. Dec 24, 2016

### Vigilant1

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True, but let's not turn a rule-of-thumb into some sort of engineering hard limitation.
1) As TF noted, the Limbach (and also the Sauer) VW derived airplane powerplants produce more than 1HP per 2 cubic inches, and are durable enough to be certified.
2) The Lycomings, Continentals, etc were designed to turn at less than 2800 RPM. The stock VW was designed to redline above 5000 RPM, and street cars can do 4K RPM for many hundreds of hours. Now, from a propeller efficiency standpoint, it would have been great if the VW engine had been designed so we could get about 1HP per 2 cu inches at 2700 RPM, but that's not the case (unless perhaps we use a wild cam and some very high compression ratios, which is not gonna give us a lot of longevity). So, we just operate them at slightly higher RPMs and use a shorter prop.
3) Piston speed has a big influence on all kinds of engine stresses (on bearings, crankshafts, conrods, etc). A faster piston needs to be accelerated and slowed more rapidly, and this is a primary source of stressses in an engine. A typical large displacement VW engine has a stroke of 82MM, while a Continental O-200 has a stroke of 98.5 mm, which is about 17% longer. That means that our VW engine at 3200 RPM (where we typically run them--or less) has a piston speed less than an O-200 at 2700 RPM. The VW is not operating anywhere near its redline speed at 3200 RPM, it's well short of it.

The VW was not designed as an aircraft powerplant, and we have to respect it for what it is. But with proper adaptations and with due respect for limitations (as we should exercise with any machine), it can provide reliable service in aircraft use, and has done that for hundreds of builders/pilots.

Last edited: Dec 25, 2016
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15. Dec 25, 2016

### Little Scrapper

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I'm not paranoid really, I just know it's easy to get a Continental and skip the pain. I'd like to warm up to VW's but after reading here I'm not really sold on them. The true usefulness of the VW is extremely limited.

I know what you mean buy Lycoming and Continental being certified but I feel that's not a fair comparison. Certified or not both companies have spent decades designing reliable engines for aircraft, not conversions. They are in the business of making aircraft specific engines and are very good at what they do.

I see the VW as a engine that can be reliable, let's be clear on that. After reading these threads I'm now discovering the engine is useless for most of the airplanes I like, besides a Sonerai, which I love.

16. Dec 25, 2016

### Vigilant1

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As you know, operating >any< reciprocating engine involves pain. They have all gotten much more reliable than the early days, but the very design is full of amazing stresses, and it's largely the wonders of modern metallurgy and fantastic lubricants that allows them to stay together at all as they try to tear themselves apart. But when a Lycoming burns a valve or needs a new jug, the $$pain$$ is a lot higher than for a VW-based engine.

Last edited: Dec 25, 2016
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17. Dec 25, 2016

### Dana

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And that is the main reason, probably the only reason, to choose a VW powerplant for an airplane. For many of us, it's sufficient reason.

Dana

18. Dec 25, 2016

### Turd Ferguson

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burned valve in a Lycoming is on the "highly unlikely" list. Those sodium filled exhaust valves are expensive but no reason shouldn't last till engine TBO. Have seen them run 2500 hrs with no issue. A new cylinder cost more, well yes, apples and oranges in many ways.

If I need a 4-stroke engine in the 50 hp range, a VW based engine is not only appealing, it's the ticket!

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19. Dec 25, 2016

### BBerson

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Right, if you need about 50hp, then consider the original VW based engines. If you need say 70hp then look at the VW based engines that are heavily modified and not much original VW.
If you need 80-100hp, like Scrapper, then a bigger engine is the only reliable option, like the o-200. Because trying to get too much power from a small engine decreases reliability.
It's more a question of suitability, not reliability.

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20. Dec 25, 2016

### Pops

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Well said. I consider a good ROC a safety factor. What is why I would never consider a two place VW powered airplane.