Harmonic damper

A harmonic damper is a device fitted to the free (accessory drive) end of the crankshaft of an internal combustion engine to counter torsional and resonance vibrations from the crankshaft. This device must be an interference fit to the crankshaft in order to operate in an effective manner. An interference fit ensures the device moves in perfect step with the crankshaft. It is essential on engines with long crankshafts (such as straight-six or straight-eight engines) and V8 engines with cross plane cranks, or V6 and straight-three engines with uneven firing order. Harmonics and torsional vibrations can greatly reduce crankshaft life, or cause instantaneous failure if the crankshaft runs at or through an amplified resonance. Dampers are designed with a specific weight (mass) and diameter, which are dependent on the damping material/method used, to reduce mechanical Q factor, or damp, crankshaft resonances.

A harmonic balancer (sometimes called crankshaft damper, torsional damper, or vibration damper) is the same thing as a harmonic damper except that the balancer includes a counterweight to externally balance the rotating assembly. The harmonic balancer often serves as a pulley for the accessory drive belts turning the alternator, water pump and other crankshaft driven devices.^[1]