Dave, I have the OEM 220 piston out. Looking up under her skirt [intake side] where the intake window is cut through, the edges of that hole are very jagged = a number of acute angles which is an open invitation for a crack to form. I can't measure it exactly but the metal in the relieved area just below the window is probably no more than .030" --just not good in that location due to the slapping of that skirt. If one did choose to run the OEM piston, There'd be a way better chance of survival if you took a file or Dremel burr and went around the inside of that window and radiused it out smoothly, then finished it with either 320 paper or a cratex wheel. I'm pretty sure that the poor metal finish in there is causing the failures.