Harmonic balancers, also known as crankshaft dampers or vibration dampers, are engine components designed to reduce engine vibration and dampen out potentially damaging torsional vibrations. They are typically made of two parts, an outer ring and a hub, separated by a layer of rubber or other dampening material. As the engine rotates, the harmonic balancer absorbs and dissipates any unwanted vibrations, helping to improve engine performance and reliability.