- The piston is 87mm, that's 1mm larger compared to the normal 86mm, and the fabric is lightweight and robust A4032 forged aluminum alloy. The required clearance of 0.In any case… If a crank incorporates a 0.02mm runout, that means it will require up 0.01mm of oil clearance because it rotates in the bearing. Don't just do we need to know how much