Crank balancers have two functions,they are first and formost a dampener for vibrations cause by harmonic frequenticies and secondly are a torsional dampener for the torsional twisting that occurrs as rpms accelerate and the rotating mass strays from its neutral alignment allowing it to return to original neutral position.It is not used as a balancer except on externally balanced assemblys where extra weight is added to the crank dampener to compensate for internal rotating componants that are not practal to be balanced close enough for mass production at reasonable cost.For instance with the advent of cast cranks that in order to balance is quite expensive,it is easier to externally balance at the dampener and flywheel.A similar reason that a sixpax balancer used offset weight to compensate for the heavy rods rather than forge a new crank with heaver counterweights.Most all cast crank applications after 1971 used the offset balancer and weighted flywheel or flexplate.Balancing cast cranks requires the use of expensive"heavy metals" or extensive lightening which can in some cases weaken them.