Knurling is typically a crutch to get you by, and generally doesn't last as long as the original skirt did. Mostly because you have less skirt surface area to bear the brunt of the piston load, as opposed to a non-knurled skirt.Just depends on the application,and what your expectations are.Cast pistons generally run at around .003 clearance on a stock street engine.Many non trained enthusiasts will try to tell you "the book" says this, or "the book" says that, and .003 is too loose. But you will(can)stick a piston if you load it heavy(tow a trailer), or run it hot if you run it tighter. I've built many Pro Stock Big Blocks that the piston clearance starts at .012, but they have a 4.600" bore or larger, and use a good quality JE forged piston. It also depends on how much taper the skirt has in it as well. An average 350 race motor for circle track with JE's will run .007 clearance on a 4.030" bore, and the skirt will have .003-.004 taper in it. With a good air cleaner and regular oil changes, those engines will run 1500-2000 laps at 7500-8500 RPM and only need about .001-.0015 of material honed out at freshen up, and ready to go again for 1500-2000 more laps. On the second freshen up, you usually need to go to .035" over and buy pistons. But by then you have raced almost 2 full seasons. Most races are 50-75 laps, 1500-2000 laps is a lot of racing.
Last edited by CNC-Dude; 11/20/08 03:31 AM.
