Quote:
kegs wrote:
no3 and it looked like it had a crack i wiped it clean and then took the rings out, whilst doing this i knocked out two broken ring lands...... i wonder what caused it ?? i got the engine hot at one stage, (no coolant) but i ran it after that and it held 135 psi across all four a few days after running hot.. maybe the slight amount of detonation i had is wat killed it???
yep, it was caused by detonation. you used black rings, didn't you? on a boosted engine it doesn't take too much detonation to crack them, then the broken pieces work against each other. sometimes they can overlap and crack the piston's headland.
as for what caused the detonation, when an engine is running hot, it will be prone to detonating for sure. It may just have been that, and it took a bit of time before the broken rings actually caused the problem.
Otherwise, as phunk said, its either leaning out under boost, or running too much timing (what have you done to control the advance?), or it could be caused by a hot spot in a combustion chamber - have you done any work to them? sharp edges can cause hot spots, but so can carbon build up.
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