The “crankshaft pulley” can be a separate part that bolts to the harmonic balancer or the pulley can be an integral part of the balancer… The term 'Balancer" is used rather loosely…It’s main purpose is to absorb torsional vibration in the crankshaft and keep them from reaching destructive levels. The longer the shaft, the worse the problem…Crankshafts tend to “wind up” like a spring as the result of power impulses delivered by the pistons and connecting rods. This winding and unwinding can lead to crankshaft failure. As Mountainbike said, the harmonic balancer absorbs this “whip” and returns it to the crankshaft out of phase with the original impulse canceling it out…The balancer consists of two parts laminated together with a rubber layer that absorbs and cancels out the “whip” in the crankshaft…