Crankshaft . The crankshaft collects and transmits to the change the power developed by each of the cylinders in an internal combustion engine . Consequently, it is one of the most important parts of the engine . In rotary motors (electric or turbine), the motor shaft is simply cylindrical , with splines for adjustment with the rotor (electric armature or turbine impeller) and gears or pulleys to transmit movement . In rotary piston engines ( Wankel type ) the crankshaft simply has a circular eccentric for each piston .

Traditional reciprocating engines have a more complicated shape (since there are cranks ), determined by the need to transform the reciprocating movement into rotary movement: precisely given its shape, it is called a camshaft or elbow shaft, in addition to a crankshaft.


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  • 1 single-cylinder crankshafts
  • 2 Crankshafts with cylinders in line and opposite or in V
  • 3 Crankshaft balancing
    • 1 Balancing objectives
  • 4 Manufacturing
  • 5 Sources

Single-cylinder crankshafts

In the early days, the typical engine combustion internal was single cylinder, and the crankshaft, to having a single crank , was completely like the old berbiquí of carpenter , called in French “vilebrequin” . The term vilebrequin is still today the French name for the Spanish crankshaft. The English call it “crankshaft” , which means tree – crank.

Each crank is made up of two arms called crank arms and the crank pin or connecting rod crank , which rotates on the connecting rod head bearing . The crankshaft rotation shaft lugs are called base lugs.

Crankshafts with cylinders in line and opposite or in V

In engines with in-line cylinders the crankshaft is made up of as many cranks as there are cylinders. On engines with opposite cylinders the number of cranks may be the same as that of cylinders or only half. On V-engines, the number of cranks is generally half that of cylinders

Crankshaft balancing

Balancing is achieved by means of counterweights applied to the cranks to obtain, when necessary, the static and dynamic balancing of the crankshaft as a whole and, often, on each of the cranks. It also serves to reduce the effect of some of the forces due to the reciprocating masses.

Balancing objectives

Reduce engine vibrations caused by the forces and moments generated by the pressure of gases in the cylinders and by rotating and reciprocating moving parts ( pistons , connecting rods, and crankshaft). Reduce the loads on the main bearings.


The material generally employed for the construction of crankshafts is steel to the carbon ; In cases of greater stresses, special steels are used, chrome – nickel or chrome- molybdenum – vanadium, heat-treated. Crankshafts are also built in nodular cast iron that have strength characteristics similar to those of carbon steel.

When, due to strong discharges, bearings with a fairly hard surface (antifriction of copper – lead alloy , duralumin , etc.) must be used, the crankshaft seals are surface hardened by cementing , surface hardening or nitriding . In a special surface quenching system widely used in series manufacturing, hardening occurs by means of surface heating obtained by an electrical procedure (by induction) and subsequent cooling with water ; this hardening system is very fast. Another surface hardening system is flaming, in which the heating is obtained with the flame. When economic problems come to a second, as in the case of racing cars, you can choose a special high-strength steel and adopt nitriding hardening.


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