Join Date: Mar 2005
Bikes: Trek, Spesh, GT, Centurion
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Replacing a chainring is trivial -- no special tools are needed, just a regular allen wrench. There's no need to replace your whole crankset unless you bent the spider also.
Remove the bolts holding the rings to the crank spider, remembering where all the bolts and nuts and washers go. Replace your middle ring -- your 4500 has a 32-tooth chainring in the middle. You can probably find one for less than $20 if you looked around. Get your Local Bike Shop to help you out.