While installing a pulley, it's always important to occasionally back off the snout a little and ensure the bolt in the nose is seated firmly and isn't loose. You also have to ensure the bigger bolt is seated firmly against the snout and also isn't loose. Don't forget to drip a little lubricant on the bolt and nut to unsure they don't sieze too.

If your snout is stripped... there's really not much you can do but purchase a new snout.

Best of luck,
Marc