Well , you've seen all those cool looking billet aluminum dash knobs, right? Think of a piston as a big knob. You put a piston in a lathe and use a knurling tool to "rough" up the piston skirt surface to give it a slightly larger diameter. Knurling doesn't take away material. It moves it. It takes metal from the flat smooth sides of the skirt and stands it up to make the piston 'Larger". Back in the time when labor cost were less than material costs knurling, lapping, shims, and boots got lots of folks back on the road.
Thanks guys, This is interesting and useful to me! Beater
