The purpose of a harmonic balancer is to dampen the harmonic vibrations that all engines produce.
Crankshaft Harmonic Balancer
The crankshaft harmonic balancer is also known as the crank pulley damper.
The crankshaft harmonic balancer is a device connected to the front of an engine’s crankshaft, usually built into the crankshaft pulley.
It sounds musical, but what it really does is disperse vibrations that travel through the crankshaft to prevent damage to it and other vehicle components.