C2 BIG BLOCK RING END GAP

[Rob A.]

I am helping a friend rebuild his '66 390HP block. The block was already "30 over", showed little wear and was not rebored. The new top compression rings were put in to measure the end gaps. Most of them were around .018-.20 with one at .023,(which I always considered about the limit). We are considering using "35 over" rings and filing our own gaps to make them smaller. Just out of curiosity we measured the end gap of one of the old rings, and it was a "whopping" .032, which according to most rebuild guides is out of limits. The engine ran fine before it was dissassembled and showed little or no cylinder taper. Are the ring end gaps not as critical as most of the rebuild manuals suggest? What is the consensus as to the allowable end gap limits on a big block?

[Clem Z.]

Re: C2 BIG BLOCK RING END GAP

you are better off with too big a end gap than too small a end gap because if the ends butt you have a bigger problem than having too large gap. for street engines that may overheat should be gapped at .005 X the bore size. race engines should be gapped at .0045 X the bore size. some piston require as much as .030 end gap because of the type of material used they hold the heat and cause the top ring to expand more.

[Rob A.]

Re: C2 BIG BLOCK RING END GAP

Since they are being reused, perhaps I should identify the piston type, which could explain the large gaps in the rings that were removed. I believe they are cast, with #242-99 stamped on the underside. When we have them balanced I'll ask the shop about the ring end gap.

[Joe L.]

Re: C2 BIG BLOCK RING END GAP

Rob-----

Hypereutectic cast usually are the ones that require a greater end gap. However, the numbers which you provided don't "ring a bell" for me. Unfortunately, except for numbers, I don't know of any way to distinguish a hypereutectic cast piston from a "standard" cast piston.