How do you remove the tension pulley on a 1992 Chevy pickup?

Hi, I have have the very same problem. I have a 1991 Chev 3/4 tonne. The long stud (bolt) keeps turning and turning ...and the pulley has become loose but won't remove...and the stud keeps turning without coming off even though I put a pry bar behind it at the same time as using my rachet! Rodney