by mike.smith » Tue May 23, 2017 10:30 pm
Required "rebuilds" I think are few and far between. And how do we define an "overhaul?" I think the kernel of the question is how reliable is a VW airplane engine, and how often do we need to do something major to it? I have never seen any quantifiable information that makes me say one VW engine is better than another (Great Plains vs Sonex, etc). Lots of personal opinions, but not much empirical data. So I'm inclined to lump most VW's together. That said...
My VW is not an example of precision German engineering. It's a wonderfully basic, simple engine that can take a licking and keep on ticking. And if it breaks down it is SUPER simple to fix. And CHEAP to fix. Believe me, I know about both of those.
At my first annual I found I had low compression in two cylinders. To make a long story short, I had run the engine too lean for too long (from my maintenance logs, about 25 hours of run time) and burned a couple of valves. Operator error. I had mismanaged what my instruments were telling me about the needle and settings I was using on the AeroInjector. Hint: if your engine is running hot and you are burning only 2.5 gph, then you are too lean! Quit doing that! It was not the fault of the VW, it was my lack understanding of the AeroInjector, and my slowness to actually do something about it. Once I changed the needle and got everything to about 4.5 gph, I have had a very happy engine. I have had ZERO issued with the AeroInjector since. I had a local engine guy replace the valves, after buying the valves from Sonex. The guy charged me $50. Try that with a Lycoming or Continental!
I had 124 hours on my engine before it became obvious from oil samples and some other evidence, that there was trouble with the aluminum Nickasil cylinders. They were being crushed by the heads and the engine was making more and more metal. I took off the cylinders and replaced a lot of parts. Because of the metal in the oil I had to tear the engine down to FULLY clean everything!
Retained: Case, crank, conn. rods, cam, heads
Replaced: Bearings, cylinders (cast iron), rings, wrist pins
None of this was the fault of the VW engine. It was the weight-saving cylinders that were not up to the task (I have my own theories why).
From 124 hours to 150 hours the engine ran like a top. ALL the numbers were better than the original build, including CHTs.
Then I had a bad day. I freak gust of wind picked up my tail while taxiing, and I had a catastrophic prop strike (one blade was found 200' away). I replaced the crank, bearings, prob hub and cam gear (though later inspection showed I did not need to replace the cam gear; I was just being cautious). To do all that I had to open the case. To my insurance adjuster the cost was a joke. He couldn't believe a new crank only cost $350.
Again, none of this was the fault of the VW. My engine has never failed (I just knocked on my wood desk!). It even kept going when the original cylinders were in hideous condition. So I HAVE rebuilt my engine, but NOT because the tried and true VW did anything to require it. I now have 230 total hours on the engine without any further issues. I change the oil and get an oil analysis religiously. I gap the valves and check all my connections.
So what is the common thread here? The engine has never failed, even when I did bad things to it. By doing regular maintenance checks and oil analysis I have been able to find every problem before it became an engine stopping event. And when I did have to "rebuild" or "overhaul" the engine, it was from operator error and not from a failure of the VW. And the costs were almost laughably low for aviation.
Since my last "rebuild/overhaul" at 150 hours (prop strike) I have had 80 hours of awesome engine operating numbers. I hope in another 200 or 300 hours I'll be able to revive the thread and report that I've not done any more dumb things to my engine, and haven't needed a "rebuild/overhaul".