It's likely stuck/tight fit. You can try tap/hammering it a little to loosen.
September, 19, 2011 AT 8:45 PM
You need to first un-thread the fan blade off and that should have been done while the pulley and belt were still in place to help hold it.
September, 19, 2011 AT 8:59 PM
Ok wait a second. What did the bolts hold on? Just the pulley? Is there a large nut on backside of fan on shaft? If so, that's what's holding it on. You can borrow tool to remove from chain auto supply store.