Harmonic Balancer - Can they be rebuilt

with a bad balancer, aside from not being able to tell where your ignition timing is at, they cannot function if the rubber is fractured, or doesnt fit as tight as designed. The harmonics it dampens can ruin bearings, and lead to crank and/or rod problems in your engine. If it were me, I would replace it. Find an NOS one if it's financially worth while, or buy a new current design.