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Ring End Gaps

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I am in the process of building an engine and the ring end gap is too large for my application. I purchased a set of oversized rings (.5mm oversize) and I plan to file them down to my target spec.

I have heard mixed opinions on this subject. I have read that using oversized rings to file and achieve the desired end gap will “oval” and distort the ring and it will cause a combustion leakage/sealing issue. I have also read that it is a common practice and there shouldnt be any worry. I’m hoping someone can provide input as to if this will cause a major issue.

Thank You!

Hi John it is common practice, But when buying oversize rings often it is just buying a different brand of the ring not actually buying a .010 piston ring, although i have seen this commonly used also with out issue,

I would be very surprised to find many new ring sets that are already too big so please measure the piston to bore clearance carefully, it only takes a small amount of excessive more diameter to make a large difference to the ring end gap.

As Ross said, the ring end gap changes rapidly with the bore diameter - by 3.1412 (pi) times the bore change*. I have done this, also, on engines where ring packs were 'pre-gapped' rather wide - if you're concerned, after gapping them place them in the bores and shine a light from the other end - you shouldn't see light coming past between the ring and bore.

*This can become very important if re-ringing in a cylinder with a bit of bore wear and taper - what may be plenty of clearance at the top of the bore may be much tighter at the lower end of the stroke, so it's critical that's also checked.

I understand now, thank you!

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