Crankshaft

Crankshaft
Image courtesy of ClearMechanic.com

The crankshaft is a hardened-steel shaft running the length of the engine that converts the linear force of the moving pistons into rotational force. To use the bicycle analogy, the cyclist’s legs are the pistons, and the pedals and crank are the crankshaft. A failure in the crankshaft or piston connecting rods typically produces loud knocking or banging sounds from the engine and represents expensive repairs in the form of an engine rebuild or replacement.