Piston ring end gap

[Nonyab]

I am looking for some sound advise on piston ring end gap. I am rebuilding an engine that has been bored .020 oversize. The required ring end gap is .008 to .014. I have tried new rings from two manufacturers and each has an end gap of .020 to .023 on the top ring, with the second ring and the oil ring being at the max. The bore and piston side clearance is .0024 which is correct.

I understand that manufacturers are notorious for their replacement rings having excessive ring end gap beyond what the engine manufacturer requires. My question is would it cause a problem if I tried to use .030 oversize rings which should allow me to set the proper end gap or would the additional oversize ring cause me other problems. I have read of others doing this. Any thoughts or recommendations, please.

John

[Doug Rodrigues]

I don't know what official publications mention about this, but personally I'd go with the .030 oversized rings and use a ring grinder to achieve the desired gap. The hand operated ring grinder can be purchased at most aircraft tool supply businesses such www.averytools.com, www.clevelandtool.com, www.aircraft-tool.com or www.ustool.com. Just make sure that the gap isn't less than minimal required as those rings do expand and the gap will lessen.

Of interest, I did bore a race car engine once to .010 that used standard size pistons with .010 rings. The drive told me that "the piston noise disappeared after a couple of laps after the pistons get real hot." I took his word for it because the clearance he had would have been way too loose even for a diesel engine!