Piston knurling is an old-school tactic for restoring function (temporarily) by taking up the clearance. Works kinda OK for low-rpm tractors n such. I have some old Caterpillar shop magazines from WWII with tips for getting a little more service from worn out engines, when all the new parts were going into wartime production and repair. Heavy ridge reaming, knurling, shimming bearings etc., anything to keep them running reasonably well. High oil consumption was to be expected lol. The old CAT Master Mechanic who gave them to me started out on destroyers in the Pacific in WWII