Crank Pulley (Harmonic Balancer)
Crank Pulley also known as Harmonic Balancer is a device connected to the crankshaft of an engine to reduce torsional vibration and serves as a pulley for drive belts.
However, every time the cylinders fire, torque is imparted to the crankshaft. The crankshaft deflects under this torque, which sets up vibrations when the torque is released. At certain engine speeds the torques imparted by the cylinders are in sync with the vibrations in the crankshaft, which results in a phenomenon called resonance. This resonance causes stress beyond what the crankshaft can withstand, resulting in crankshaft failure.
In order to prevent this vibration, a harmonic balancer is attached to the front part of the crankshaft. The damper is composed of two elements: a mass and an energy dissipating element. The mass resists the acceleration of the vibration and the energy dissipating element absorbs the vibrations.
Moreover, the energy transferred from the piston to the crankshaft can induce as much as 2 degrees of twist in the crankshaft, which has many follow-on effects on all engine elements that require adequate timing such as valve opening, cam timing, ignition timing etc.