I have bought pistons for a 70's 400 ci Pontiac Firebird to be fitted in the cylinders. My dad has been doing the task of fitting them on to the piston rods. This did not go easy. Getting the old 370 pistons off of the rods was hard work as the crank pin was not coming out untill a load of pressure was used. For assembling the new pistons to rods was easier but still needed to be cautious. If the crank pin is not sitting well or there is a bit of dirt in the way, it can break the piston or the rod. But my dad has put a lot of effort and care into it and succeeded!