Harmonic balancer coming off engen.

I broke down on the side if the road with a
broken belt. I called a mechanic friend of
mine to help me he told me that the
harmonic balancer was coming off. He
replaced it for me but told me the
crankshaft was sticking out further then it
should be so he pushed it back in. Less
then a week latter once again the harmonic
balancer is pushed out. Any ideas on what
could be causing this? I have never heard
of a crankshaft coming out and neither has
any one else I have asked.