Lapping piston rings

[Alan Nyhus]

Herman showed me his lapping setup. It was a piece of aluminum round stock that had a recess machined into it that was .061 deep for 1/16" (0.625) rings. When he ordered the pistons for Super Stock motors (BRC, generally...some Venolias), he spec'd the ring grooves at .061. The ring would go into the aluminum holder and he put some Comet mixed with parts cleaner solvent on a big piece of thick plate glass and rubbed the fixture in a circular pattern, checking the fit of the ring to the groove as he went.He had the same holder for the .043 rings..probably some others as well.

On the Stocker pistons with the 5/64 grooves, he would tighten up the ring lands by lightly dimpling them with a small punch and lap the rings to the now-tighter grooves.

With the advent of CNC equipment, the need for a lot of this is gone.

Anyway, that's how I remember the process.