Hi Pete,
Well, we are all a bit cray but no, you are not alone :)
The engine I had was rebuilt by a Rotax Repair Center (actually recommended by
Rotax). Had a number of very unique issues with this engine until I decided I
wanted to spend more time flying than learning how to fix a Rotax (which I
really
did!) so I bought a new engine (honestly, best investment in my airplane so
far).
But I saw no evidence of case fretting.
One day I will repeat the analysis with the new engine just for the fun of it.
But I can tell you that with the new engine the feel is very different.
BTW, after a long chat with Phil Lockwood he explained to me how a simple issue
with an older gearbox could cause vibration in the same way I was feeling.
Basically
a small depression where the clutch dogs rub. If this is not caught during
rebuild he says it can generate vibration and it feels as if a switch was
flipped at very specific RPMs. My gearbox had been "rebuilt" but who knows.
My lesson with the Rotax so far is that it is a wonderful engine but a bit
finicky.
It seems that small things will make it run not as smooth. But maybe I am
wrong in my assessment. We will see how my experience with a new engine from
the start is.
Best Regards,
Chris
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