JW51 I have seen where the pumper took a center punch and just covered a 52 fairbanks-morse oilfield engine piston with deep centerpunch marks same thing as a knurl. They would then file till it went in the cylinder,wash in coal oil put it together. Slow running engine,well worn from dry "field gas". In 1972 when I built a machine shop in the local parts store we got a new knurling machine. Some racers liked to knorl their pistons to hold oil,I just did what they paid for !!
