Originally posted by Flypaper
Used to work in an automotive machine shop.The auto pistons are cam ground,in other words oval shaped, with the fattest part 90 degrees to the wrist pin. They are designed to expand and contract along the pin direction so they can get away with .0015 clearance on average depending on the diameter of the piston.
Well, they're not ground. They are turned with diamond tools. (and axially they are also barrel shaped)