A crankshaft—related to a crank—is a mechanical part able to convert reciprocating and rotational motions. A reciprocating engine translates the piston’s reciprocating motion into rotational motion; a reciprocating compressorconverts the rotational motion into reciprocating motion. To do the conversion between two motions, the crankshaft has “crank throws” or “crankpins,” additional bearing surfaces whose axis is offset from that of the crank, to which the “big ends” of the connecting rods from each cylinder attach. It is typically connected to a flywheel to reduce the pulsation characteristic of the four-stroke cycle, and sometimes a torsional or vibrational damper at the opposite end to reduce the torsional vibrations often caused along the length of the crankshaft by the cylinders farthest from the output end acting on the torsional elasticity of the metal.

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