Heavy cases cracking

woxof

Pre-takeoff checklist
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May 6, 2015
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woxof
Has anybody else had crankcase cracking problems. Sounds like they may not be any better than the light ones.

"....when it was torn down, my engine looked much as he would expect of a big-bore Continental run to TBO and beyond. The lifters had some spalling; the oil cooler was rejected because of a crack; and the starter adapter shaft and gear were worn beyond limits—all common findings. However, one important and expensive part didn’t pass muster: the crankcase. After cleaning and upon inspection, Pinnacle discovered a crack that was not repairable. Cha ching! An overhauled case added $6,500 to the bill. The original was a “heavy” case—as opposed to earlier models with thinner cases. The thicker, heavier cases were introduced to reduce cracking, but Kuti says they see a fair amount of cracking of heavy cases. It may be too much of a good thing, he suggests: the heavier cases don’t flex under stress, which may lead to cracks. Nonetheless, that is still the recommended case."
 
I have been told that the light cases do not crack more frequently; this, by a very detailed and anal A&P/IA who has flown his bird around the world 3 times, all behind a light-case 520.

In any event, my plane had a heavy-case, and it cracked most spectacularly.
 
Could this be inadequate preload on the through studs? Were there signs of fretting on the cylinder base-crankcase interface or on the adjacent main bearing seat faces?
 
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