just to clarify...i have had the block re bored to +0.5mm and have fitted o/size pistons & rings. Unfortunately when i fitted the pistons to the block i chipped the edge of the top ring on one piston, the second ring on that piston is the correct one as is the oil control ring. Rather than purchase a full set of o/s piston rings to use just one i considered whether it is a viable option to use a standard top ring on the one piston. Obviously not an ideal option but seeing as i have a set of standard rings i was interested in any constructive advice......

apologies -- please read the post i put up yesterday on the topic of o/size pinto bores to understand why i felt it necessary to clarify

Although this may work, and the engine run, you will never get the ring gap correct and have lower compression on that bore due to poor sealing of the ring against the bore.

Contact the ring manufacturer and try and get a single.

Rings should be fitted to the bare bore without piston and the ring gaps measured with a feeler gauge, to small a gap is as bad as to big a gap.
I would think the standard rings could give to large a gap.

Not only will the ring gap be wrong but the ring tension (which I think is more important) will be wrong as well, causing serious sealing problems and wear problems as well.

Not sure what engine it is - if a modern engine, they rely on tight tolerances to perform well so don't do it. If an older motor like a crossflow which you are going to keep below say 6500 revs it's less of a problem but it seems a pity to compromise a motor for the sake of a ring or a ring set for one piston.

I know why your asking, but there isn't really any way out of this - you'll need to get a ring the right size

as r1_pete says, you may be able to get a single ring from the manufacturer (which type are they? )

[Edited on 23/9/2010 by mcerd1]

the pistons are ae pistons the engines a pinto