Crankshaft

[7] The number of main bearings is determined based on the overall load factor and the maximum engine speed.

[1] Most modern car engines are classified as "over square" or short-stroke,[citation needed] wherein the stroke is less than the diameter of the cylinder bore.

[citation needed] In some engines, the crankshaft contains direct links between adjacent crankpins, without the usual intermediate main bearing.

[20]: 16, 41  This arrangement is sometimes used in V6 and V8 engines, in order to maintain an even firing interval while using different V angles, and to reduce the number of main bearings required.

Today, manufacturers tend to favour the use of forged crankshafts due to their lighter weight, more compact dimensions and better inherent damping.

Cast iron crankshafts are today mostly found in cheaper production engines where the loads are lower.

Though the fiber flow (local inhomogeneities of the material's chemical composition generated during casting) does not follow the shape of the crankshaft (which is undesirable), this is usually not a problem since higher quality steels, which normally are difficult to forge, can be used.

However, the automatic crank mechanism described by the Banū Mūsā would not have allowed a full rotation, but only a small modification was required to convert it to a crankshaft.

[27] The Italian physician Guido da Vigevano (c. 1280 – c. 1349), planning for a new Crusade, made illustrations for a paddle boat and war carriages that were propelled by manually turned compound cranks and gear wheels,[28] identified as an early crankshaft prototype by Lynn Townsend White.

[29] Crankshafts were described by Leonardo da Vinci (1452–1519)[26] and a Dutch farmer and windmill owner by the name Cornelis Corneliszoon van Uitgeest in 1592.

Internal combustion engines of early 20th century automobiles were usually started with hand cranks, before electric starters came into general use.