A crankshaft—relatit tae crank—is a mechanical pairt able tae perform a conversion atween reciprocating motion an rotational motion. In a reciprocating ingine, it translates reciprocating motion o the piston intae rotational motion; whauras in a reciprocating compressor, it converts the rotational motion intae reciprocating motion. In order tae dae the conversion atween twa motions, the crankshaft haes "crank throws" or "crankpins", additional bearing surfaces whose axis is offset frae that o the crank, tae which the "big ends" o the connecting rods frae each cylinder attach.


It is teepically connected tae a flywheel tae reduce the pulsation characteristic o the fower-stroke cycle, an whiles a torsional or vibrational damper at the opposite end, tae reduce the torsional vibrations eften caused alang the lenth o the crankshaft bi the cylinders farthest frae the output end actin on the torsional elasticity o the metal.