An engine’s crankshaft is the main driving shaft which captures the two-way motion of the pistons, and converts the planar motion of the pumping pistons into rotary motion. The pistons are connected to the crankshaft by the connecting rods.

The crankshaft is not only intimately related to the camshaft, pistons and connecting rods, but also the valves, cylinder head and timing belt. All of these particular engine components must operate perfectly together so that the timing is impeccable; engine operation will cease otherwise. If any component fails, then major engine damage will occur. Although extensive tests are carried out in new engine designs, crank-shaft failure does occur. Crank shaft failure can be attributed to manufacturing or material defects, but these are, fortunately, few in number. Crankshaft damage and overheating can also be caused by poor engine maintenance as a result of the bearings being starved of oil (ouch!)

How a crankshaft is designed varies with the number of cylinders and how the cylinders are arranged. Four-cylinder engines have a shorter crankshaft design than the bigger 6-cylinder and 8-cylinder engines. A V8 engine has a shorter crankshaft than its straight-eight cousin.

Crankshafts can be forged from a steel bar or cast in ductile iron. Modern car manufacturers tend to favour the forged crankshafts because they are lighter and have better inherent properties.

We hope that helps answer the question ‘What is What is a Crankshaft?’!

Back to Car Glossary