When does a VW make sense?

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orion

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While I would never argue against a certified engine for someone who wants one, part of the issue here is that $5,000-8,000 would buy you an complete brand-new VW-conversion engine and all-new accessories, instead of just an overhaul. The overhaul on the VW, even a major, will only be a fraction of the top-end overhaul price on the certified engine.
But keep in mind that for an Experimental you can use after-market parts and do the work yourself. As such, the cost to overhaul that Cont. is actually much closer to the VW than commonly published numbers might suggest.
 

PTAirco

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True, there are folks out there who get extended usage, some by quite a bit, but last I heard the average life of these small engines is in the range of about 200 hours. So you may have to figure the increased frequency of rebuild or maintenance into your cost numbers when comparing the auto alternatives and the certified engines.
I would say if you only get 200 hours out of a VW conversion, you are doing something wrong. A friend of mine has a turbocharged VW in his KR2, and recently pulled it out after 600 hours, more for tinkering purposes than necessity. I have known at least one 1000 hour VW. These may be the exception, but I feel that the operator and how it is maintained and flown may be more to blame than the engine itself.
 
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Mac790

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I would say if you only get 200 hours out of a VW conversion, you are doing something wrong.
I think it can be realated with rpms, maybe they cruise only at 50% rather than at 75%. Generally car engines don't like higher rpms. It's hard to judge without more details. You know oil type, rpms, propeller size, etc.

Seb
 

Topaz

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I would say if you only get 200 hours out of a VW conversion, you are doing something wrong. A friend of mine has a turbocharged VW in his KR2, and recently pulled out out after 600 hours, more for tinkering purposes than necessity. I have known at least one 1000 hour VW. These may be the exception, but I feel that the operator and how it is maintained and flown may be more to blame than the engine itself.
Yeah, that's more in line with what I've heard over the years, as well, and not just for guys that "baby" the engines by running them at less than 75% power.

200h TBO? With absolutely all due respect to Orion's far greater experience, if that were the norm I think I would've heard about it over the years. Many, many of the much older conversions (pre-1980's) had heating problems induced by inadequate cowling/baffling provision, and I know that before oil coolers became pretty much standard (again, 1980's) that such a life may have been more common, but now with those factors far better understood and addressed, I find a 200h average TBO rather hard to believe.

And again, with all due respect, my glider club services as much of our O-540's (in the towplanes) as we can (a member is an A&P), and even though we're doing the work ourselves, to say that overall costs are anywhere even remotely close to what it would cost to do the work on an auto conversion is a bit of a stretch, too. I understand that this work is with certified parts in a certified engine, but we're not really paying any labor on most of the work.

I'm not saying that auto conversions are better than certified. Most of the time, they're not as good, IMHO. But the VW conversion has over fifty years of development on it, and it's about as bullet-proof as you can get in an converted auto motor. Granted, I'm talking about modern conversions that use a forged crank and better accessories, a dedicated oil cooler and such, instead of the old-style "plug in a magneto, key a prop-flange to the pulley end and go fly" conversions.

Perhaps that's where the radical difference in perceptions is occuring.
 
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orion

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My information may be somewhat dated - the causes I remember were an issue of redrive wear and fatigue, improper cooling (valve problems and premature ring failure) and main bearing wear due to sporadically insufficient lubrication (which could also be a cause of the ring issue). However I have the feeling that this dates back a ways - I also know a few airplanes (BD-5s) that have accumulated a bit over 700 hours with no issues.

Nowadays I think the bottom line is simply that if you want a good long life out of your engine you must use it. The most damage occurs as a result of long periods of inactivity and in that case no engine, certified or otherwise, is immune.
 

Topaz

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The heat-related lubrication problems you mention are the ones I remember, also, and IIRC, were the reason for the big push towards oil coolers by GP and Revmaster back in the '80's. Especially as the higher-output conversions were coming online for the Q2, bigger KR-2's, Dragonfly, and the like, I remember a number of articles being published with oil coolers suggested as a mandatory item for VW conversions of almost any output. The stock VW auto setup doesn't really provide much oil cooling, and the oils of the time were breaking down under the extended high-power load and causing all sorts of devilry in the engines.

It was also a highly-recommended modification for my 914 (basically running a Porsche-reworked Type 4 engine with fuel-injection and a different cam) for any kind of time trials or racing. Oil temps could climb quite a bit under that kind of usage, and oil life dropped drastically without some kind of dedicated cooler.
 

Mac790

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Topaz

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Have you seen a post by radfordc about VW engines?...
I have. I don't know what happened with his, and I'm sure it must've been terribly frustrating for him. However, his experience is counter to what I've seen in most late-model (post-1980's) full VW installations.

I'll admit that I know little of the 1/2 VW engine conversions. I've never really studied them much, and most of the time I've been interested in larger aircraft that take the four-cylinder 'full' model engine. It's a neat little engine, at first glance, but I would imagine that all the machining and welding must be done very carefully, lest one mess up the alignment of critical parts within the engine. Don't know if that was the root of radford's problems, or if it was something else entirely. He certainly seems to have gotten a lemon of an engine in that particular case, unfortunately, and seems to have had trouble with a four-cylinder conversion as well. If it were the root coversion of VW's for aircraft use that was a fundamental problem, I find it hard to believe that it would've stayed such a "secret" over all these decades. It's not like the conversion has been rarely done.
 

Midniteoyl

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Seems to me that the redrive and heating issues would be the most common failures, as orion suggests - but - premature wear in the bearings and rings could largely be remeadied with the use of modern parts, ie: 3/4 grove crank bearings and low tension rings. Having pulled apart several late '90's engines recently, I am amazed at the very small amount of wear compared to earlier ones. A Vortec I pulled with over 110K miles had no ridge in the cylinders and no scuffing of the bearings, was cleaned, belts and water pump changed (still working) and put back into service... and thats now the norm.
 
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