Keith sez...
> Thanks to everyone who replied to my previous posting. The general
> concensus seems to be that too weak a mixture, poor cooling or too hot a
> plug are to blame, although the plugs are correct (L87YCC), and it didn't
> show any signs of overheating or weak running.
>
> I got the lump out yesterday and finished off stripping it down. It
appears
> that the problems with that engine were more widespread, when I took the
> pistons out ALL the top piston rings were broken. I'm beginning to think
> that the ring failure could have been the cause of the demise of piston
> no.3, if the second ring had broken as well then a lot of hot gases
would
> try to get past the oil control ring, resulting in molten aluminium. The
> gap in the oil control ring was directly below where the piston failed.
> The question is why did they fail? They were new (+30) hepolite pistons
in
> new bores.
>
I would pay close attention to your distributor advance system. Too early a
spark will play havoc with the top rings and piston crowns. Misadjustment,
weak springs and incorrect vacuum routing can all cause this. Also check to
see if someone put a new set of rings in a bore that was not just recently
bored. There will be a step where the top ring stops in the bore and if you
put new rings in, they will often break. Many piston ring makers sell a set
of rings that are stepped on the top ring to prevent this problem.
My personal advance system is set WAY to fast...
Nick in Nor Cal
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