Crankshaft

Connecting rods link each piston to an offset journal on the crankshaft. As combustion pushes the pistons down, the crankshaft rotates. It runs in main bearings in the engine block, lubricated by pressurised oil. The crankshaft also drives the camshafts through the timing chain or belt, and the auxiliary belt from a pulley at the front. A flywheel or flexplate at the rear connects it to the clutch or torque converter.

The crankshaft is made of forged or cast steel or iron and turns in main bearings in the engine block. Counterweights balance the forces of the pistons and connecting rods.

Counterweights balance the forces of the moving pistons. Oil from the pump reaches the bearings through drillings, forming a thin film so metal does not touch metal. At its front end the crankshaft drives the timing belt or chain and the auxiliary belt; at the rear it carries the flywheel, which connects to the clutch or torque converter.

Bearing wear from low oil pressure causes a deep knock that rises with engine speed, a serious warning sign. The crankshaft position sensor reads a toothed wheel on the crankshaft and is essential for the engine to run. Crankshaft damage is rare but serious, usually caused by oil starvation that destroys the bearings. A deep knocking noise from the bottom of the engine is a sign to stop driving immediately.