There are more Rotax 912 around than Lycoming 320/360. Most of the Lycomings are certified, most of the 912s are not. Still, failures with a 912s are rare, failures with Lycomings are happening all the time. Maybe not catastrophic failures, but cracks and valve related failures. That is my impression.
The important thing is that there is nothing going on at Lycoming to improve the engines. They are just producing overpriced parts using manufacturing tools from the 50s and 60s. It's like the old east block countries before the wall fell. They did the same producing 50s and 60s type cars, copies from western Europe, at least they had the decency to sell them cheap. The Lycomings are good engines, the engineering done when they were designed was top notch. But thing has happened since the 60s. Cylinders don't crack anymore, valves don't burn and so on. And if they do, then things are redesigned so it won't happen again.
What you say may be true in Europe, but the opposite is true here stateside. I have a friend with a 7/8 scale Storch he built, 912ULS. He keeps temps well monitored and in line with guidance. So far he's had an in-flight failure caused by using auto fuel (water entrenchment?), a broken head stud (as best as we can tell, caused by detonation) and 4 cracked mufflers. ~300 hours on it.
Rotax 912UL installed on a CTSW, factory motor, <90 hours on it since new, low oil pressure problems, temps exceeding redline, seems like it wasn't broken in, but Rotax said no break in required?
Rotax 912 Certed as installed on DA20A. Spent 10 or so man hours on the bing carbs balancing, prop balancing, to try and figure out a vibration problem. Turned out to be the gearbox trying to eat itself.
That is the extent of my experience on Rotax 9xx series engines... not just the bad experiences mind you, but all of them.
Lycoming and Continental have incrementally improved their engines over the last 50 years, to the point that I'd be willing to bet that not ONE part number is the same in a new O-360A1A as one that was built in 1960. My current Citabria motor is from 1969, has two original cylinders (and two that have been replaced) never been split, and has 2400 hours on it, Still runs strong, although it's getting replaced soon, due to camshaft wear. With roller tappets and the improved oiling available today, I'd not be surprised to be able to get 3500 to 4000 hours out of a new manufacture 150HP O-320.
The same flight school that operates the CTSW from the 912 example recently got 2400hrs out of their 2006 DA40's IO-360 before replacing with a factory rebuilt. While these engines appear to be unchanged and lacking in technology, they are really very carefully engineered to do what they do, and nobody has really been able to do it better.
Theilhart tried to best the O-320 market, and failed quite dramatically.
