what needs to be replaced?? the pulley or the harmonic balancer??

the harmonic balancer is 2 shafts that are inside the engine that turn at twice engine speed and in the oppisite direction... these "cancel" out a lot of engine vibrations to make the engine smoother, especially at idle.

what you pictured in red is the crank pulley... but the part that drives the timming belt and harmonic balancer belt...