Did you heat the gear before installing it? Get it just hot enough to need a welder's glove to handle it, and it will slip on all the way to the bottom without hammering on it at all. Too late now, I know, but you might consider pulling it back off and cleaning up any burrs the hammer job created, then heat it with a Propane torch.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!