Graeme, I dont know if the following is of any relevance to you but I had a
history
of identical cracking to yourself on my 912ULS. Both rear down pipes,
twice each side. The photo attached shows the first time one went. Also
numerous
springs lost too.
My engine was second hand to me, I had the first down pipe crack within 5 hours.
Although the engine was generally very smooth running I had an ongoing problem
with vibration immediately after starting (NOT kickback) and also when
throttling
back during descent after cruising flight (unloading the prop). This
high frequency vibration was teeth chatteringly severe but only lasted a few
seconds each time. I learned to live with it by modifying my starting
technique
and my initial descent technique but looking back now I fully believe it
was this that was causing my exhaust to fail.
On my description, Kevin Dilks immediately diagnosed it to be worn prop shaft
splines.
He said this was common on ex-weight shift microlight engines which mine
was, due to their foot-throttles and very slow idling RPM habits. Kevin
fitted a new prop shaft and the result was absolutely fantastic. All vibration
problems completely gone for good and the engine is now like a sewing machine.
Touch-wood my exhaust has stayed in one piece since and Im very much hoping
that issue has been cured too....!
The new prop shaft was seriously expensive and I put it off for a while but it
was actually the best single payment for maintenance that Ive ever made on the
machine.
--------
G-TERN
Classic Mono
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