Marshall,
When driven on, you are striking the center portion of the balancer. The outer portion is held to the inner portion with a vulcanized rubber ring. That outer ring is heavy and has a lot of inertia. When you smack the inner part, you stress the rubber joints between the inner and outer parts of the balancer. If you are lucky, you didn't damage it, but if it wobbles, something is screwed up. Either it isn't straight on the bore or the rubber joint has failed. Drawing it on without a hole in the crank is almost impossible when it is still in the rig.
