There is another problem that occurs when the crankshaft pulley - I am not sure that it is actually a "harmonic balancer" - is loose:
The key and the keyway that holds the timing belt gear - and the attached crank pulley - in place gets wallowed out because a mechanic/previous owner did not properly tighten the pulley bolt on the end of the crankshaft. This causes the timing to advance and/or retard which is a very bad thing!
Many have cleaned up the damage a bit and JB-Welded the key back in place, solving the problem. Unfortunately, this fix can make it difficult to replace the oil pump, should it fail.
The ultimate repair is a new/remanufactured crankshaft.
Get a flashlight and a little mirror-on-a-stick tool and inspect the end of the crankshaft to see if the bolt has worked loose. It may be necessary to remove the radiator fan to make room for the inspection...
I hope that this helps!