Yep-- - -you lost the spacer. It's a ring about 3/16" thick that fits between the fan and the bearing. I use a 1/2" drive impact wrench to tighten the pulley nut- - - -it needs to be TIGHT! Wrap a belt around the pulley sheave to hang onto while you hammer the nut down with the impact.

Edit: Alternators don't have a key- - - -the friction fit does all the driving.
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!