The Long Piston Stop is a necessity for performing leak-down tests and valve seal replacements on HEMIspherical engine designs.

Prevents shop air from rotating crank shaft when removing valve stem shields.

Once installed, it holds the crank shaft in place so shop air can be applied to a piston that is at top dead center.

Up to 100 lbs per square inch of shop-compressed air can be applied to a cylinder at the top of it's stroke with valves closed. (This pressure holds the valves in place, allowing the valve stem seals to be replaced without taking the engine apart.)