That part of the engine which transmits the reciprocating motion of the pistons to the driven unit in the form of rotary motion. That part to which the connecting rods are attached.

In the case of many of the older stationary engines the crankcase was open.

Open crank stationary engine.

The three main components of a crankshaft:

  1. Big end - small shaft that locates the conrod and reacts the force transmitted from the piston.
  2. Main journal - this carries the crankshaft in the main bearings and reacts all of the forces.
  3. Crank webs - connect the big end to the main journal.

Crankshaft for a 4 cylinder in-line engine.


Series of weights attached to or forged integrally with crankshaft & placed to offset reciprocating weight of each piston and rod assembly.

Crankshaft Gear

A gear mounted on the front of the crankshaft that is used to drive the camshaft gear.

Crankshaft Journal

The journals running in the main bearings as opposed to those for the big-end bearings.

Crankshaft Pulley

A wheel attached to the front end of the crankshaft which is connected by fan belts to the fan, the alternator, and other devices so that the rotating crankshaft can drive these other parts as well.

Crankshaft Sprocket

A chain-sprocket mounted on the nose of the crankshaft which drives the camshaft by means of a timing chain.

Crank Web

One of the pair of arms which carry the big-end journal.

Position Sensor

A sensor which sends information concerning the precise position of the crankshaft so that accurate ignition timing can be achieved.


A term used to describe how much a crankshaft is bent.

Throw of Crankshaft

The distance between the center of the crankpins and the center of the journals of the crankshaft. It is equal to half the stroke of the engine.

See also: Big End, Connecting Rod, Crank, Crank Web, Crankcase, Crankshaft Journal, Crankshaft Pulley, Internal Combustion Engine, Timing Chain, Timing Gears, Top Dead Centre.

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Subjects: Engines