Hi,
While it is possible that it is just a matter of re-torquing the crank bolt, you need to check for messed up threads inside end of crankshaft where crank pulley bolts goes in. Unless you are hearing a loud knocking noise like a piston slap, I dont elieve that you are dealing with a broken crankshaft. If threads are messed up, it is possible to re-thread, but I would recommend having a professional do that. Unless there are other issues with engine, I wouldnt rebuild unless necessary.
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