The crankshaft is one of the most important parts in the engine. It bear the force of connecting rod came, and turn it into a torque output and other attachments on the engine with the crankshaft. Periodic changes in the quality of the crankshaft is rotating centrifugal force, gas reciprocating inertial force and inertial force work together, make the role of crankshaft bending under torsion load. So the crankshaft has enough strength and stiffness, shaft neck surface need to wear uniform, work, good balance.