crankshaft

A crankshaft is a rotating shaft with offset crankpins connected to the pistons via connecting rods. In four-stroke engines, the crankshaft converts the reciprocating motion of pistons into rotational motion that powers the vehicle and drives ancillary systems.

The main body includes main journals for bearings, crankpins or throws for each cylinder, and sometimes multiple throws per crank. The distance from center to crankpin (the throw) determines piston stroke. Connecting rods link piston pins to crankpins. Most designs include counterweights to balance the reciprocating masses and reduce vibration. Fillets at transitions, oil galleries, and end sections for flywheel mounting and timing gears are typical features.

Materials and manufacture: for mass production, crankshafts are cast from ductile iron, compacted graphite iron, or steel; higher-performance units are forged from steel. Finishing operations include precision grinding, heat treating, shot peening, and surface hardening. Some are designed with modular construction to ease manufacture.

Balance and maintenance: engines rely on static and dynamic balancing; incorrect balance or out-of-balance condition can cause vibration and bearing wear. Crankshafts require proper lubrication via oil passages, and regular maintenance is needed to prevent wear and fatigue cracks, especially at fillets and at crankpins.

Applications and failure modes: used in automobiles, trucks, motorcycles, aircraft engines, marine and stationary power plants. Common failure modes include bearing wear, fatigue cracking at fillets, torsional twisting from overheating or over-revving, and oil starvation.