[Jacksonlll]

Your tapers don’t match. Tightening the nut does nothing. Get a new fan that fits tightly on the shaft and matches the shaft taper. Don’t run you fan belt tight. As loose as possible that will still run your generator. A tight belt will hammer out the taper on the fan hub.
Or, get some shim stock and fit it place to make a better match to the taper. That’s usually a field fix to get you home. Have a lot of bandaids. Those shims are sharp. Good luck.