Very fine grade file in a vise. Grip ring with its gap over file so both ends will be grinded when squeezing it over file.
Move so file will grind from outside of ring to inside. You'll feel which way the file need to sit in vise.
If burrs will crack, it is on inside and no problem.
Worse if filing from in to out which is a no no.
I use a needle file from a set I have in different shapes. The flat one.
Make sure to grind the corners of ring ends to remove burrs sticking out.
I use a grit 400 paper.
Outside will scratch bore, inside might make ring harder to compress completely shut when mounting the cylinder.
Even good JE pistons with new Wiseco rings had sharp burrs sticking out. Easy to feel with finger over ring to end, nail hook into stickouts.
Some oil rails can cause problems if they want to hook into the expander and not fully compress. Filing the inner corner of the thin rails will avoid to hook into expander.
Maybe mostly Wiseco XA rings with very thin rails. (The 2 rings placed outside the expander making an oil control ring).
Check gap in bore in time before filing too much.
Press ring down the bore with help of piston so ring will sit correct and easier to measure with feeler gauge.
