Had a heck of a time, even with an air impact, getting the Alt. pulley on tight enough (I went through 3 Alt's AND pulleys) so it wouldn't spin on the shaft. These newer Alt's don't have a key/ keyway to keep them in place. They are held in place by the nut's pressure only. Be sure to paint indicator marks are the pulley & Alt. shaft & check frequently to insure it's not slipping. When they slip, it wears the ID of the pulley & the OD of the Alt. shaft, destroying both. The external fan of the cheaper Alt's can do a lot of damage too, that's why I went to the 100 Amp just to contain the fan internal to the Alt. housing.