There's a tec tool that's used to hook into the intake port , then the skirt of the piston comes down and sets on it. The tool is .110 thick, the measurement off TDC that it must not exceed is .775 so after you set the exhaust height with gaskets, then you check that intake off TDC and cut the skirt accordingly, after cutting length you can legally cut a champher on the piston skirt not to exceed .030. Jon