Do you have an aftermarket underdrive pulley? If so, they are bad news. The stock pulley has some kind of a damper in it to reduce vibration in the crank. The aftermarket ones don't, and therefore put lots of wear on the bearings inside the bottom end. If you have a stock pulley, you should be able to get away with just tightening it, unless damage has already been done to your engine. There is a little key that goes in the crankshaft to keep the pulley aligned and the bolt on the crankshaft has to be torqued to some ungodly amount (something liike 200-250 ft-lbs) You should just be able to tighten it with a REALLY good impact gun and a big compressor (like real professional shit). Unless you have stripped the hole for the bolt that holds the pulley on; In which case you are F-U-C-K-E-D. FUCKED!