Piston oil ring gap

[andrew neville]

Hi
What would be the recommended Oil ring gap for a Mahle 82.5 mm piston please. ( New installed)
Thanks
Andrew.

[C J Murray]

I guess you are dealing with a one piece oil ring? Modern multi piece rings don't require gapping, just a quick check. I would use the same gap as the lower compression ring. Being low on the piston the ring will not expand much.

[andrew neville]

Yes it is a one piece oil ring . The original broke on installation it appears that it was too long . The 3 other cylinders went on without any issues . Interesting that 3 pistons had the same markings but this one with the issue has a different 3 digit number but it could mean just the batch build number ?
Thanks for responding CJ.
Andrew

[Ron LaDow]

Rule of thumb for air- or water-cooled engines is .004"/1inch of bore, so say .0013" or so.
Cliff's right, the oil ring is going to expand by the oil temp, rather than the chamber temp, so you could cheat a bit. But how much?
What gap are you finding in the supplied part?

[andrew neville]

Thanks Ron we ended up pulling another cylinder and measuring the gap , it was 0.012" so I filed the new oil ring to suit. We have the engine finished and have test run it.

[Ron LaDow]

Sorry for the missed decimal - should have been .013"