Originally Posted by zoodude

It would most likely be easiest to either call shimano or look up what kind spline your bottom bracket is. Either square or diamond would be my guess. From there grab a replacement crank set. As for which one, just match how many teeth your crank currently has as close as possible so that it will be a close replacement in gearing and fit your front derailleur. From there you should also replace your chain and rear cassette/freewheel. All the parts of a drivetrain stretch together and if it is stretched enough that it is slipping on your crank, most likely the rest is pretty bad. It is good practice to replace the chain and cassette/freewheel together and the crank when needed. Finally, if you do decide to use my suggestion you will need a crank puller to get the cranks off. A simple little tool that makes your life ten times better!