Crankshaft harmonic balancer reduces engine vibrations

A crankshaft harmonic balancer is an important engine component that is attached to the front of an engine’s crankshaft, which is generally built into the crankshaft pulley. The primary function of a crankshaft harmonic balancer is to alleviate and absorb the vibrations caused due to the rotation of the crankshaft.

Source: http://www.jskautomotive.co.uk/blog/symptoms-bad-crankshaft-harmonic-balancer/