Interestingly enough, in this month's Sport Pilot, p 31, there was an article about an Engine failure survey: Of note:
* of 3200 aircraft registered with RAAus, 429 responded to the survey.
* of those 429, 1/3 were Jabs, 1/3 were Rotax 4 strokes, and the rest were lycomings, 2 strokes, VW, etc.
* of those, 1/5th (or about 100) experienced an engine failure - most jabs being for thru bolt, piston/ring, exhaust valve and most rotax for sprag clutch issues, CDI or electronic ignition failures, or gearbox problems.
The survey is still open as far as I know, and full analysis and results aren't available.
Maybe concerned parties (or everyone really) should take the survey to help build an accurate picture?
Of course, in typical style, they say "information is available on the RA-Aus website", which buggered if i can find it. And they provide a link which contains roughly eleventy-billion random numbers and letters in the hyperlink - ever heard of tinyurl, guys??