Broken Rings - What causes this?
 

A friend of mine is doing a rebuild of a 944 n/a motor. It ran, but not well and was down on compression.
Upon disassembly, he found that one of the pistons had a crack, and all the top rings were shattered...

The rest of the rings were intact.

Bores were still in decent condition.

I'm curious to learn what would cause this?

He did say it looked as if it had been rebuilt before as it had a turbo head gasket.

Insufficient ring gap?
Incorrect rings?
Over heating?

It's a stock n/a motor so I don't think it would be a detonation problem..
Thoughts?http://forums.pelicanparts.com/uploa...1599173718.jpg
http://forums.pelicanparts.com/uploa...1599173718.jpg

Mike, looks like miss detonation or too much play in the ring grooves
Bruce