What's the reccomended piston skirt clearance on an air-cooled Harley engine? If it's anything like the Lycoming aircraft engines I've built, it's several times that of an automotive engine. The pistons flop around like a BB in a boxcar until the engine reaches normal operating temperature, and the 65 HP Continental in the Aeronca Champ had a nasty habit of seizing up on takeoff in hot weather unless the pistons had very sloppy clearances. Yes, ring end gap is important, but the ring has to be round to start with, and it's got to match the cylinder bore before the end gap is cut during the manufacturing process. At least that's what Perfect Circle told me when I attended, and aced their 3-week Doctor of Motors training school with a 96% grade average.
Jerry
