I've got a 2002 61" Scag Turf Tiger. Bought the spindle powered Scag vacuum system for it. Haven't used it for any extended amount of time for most of the summer. Used it yesterday for about 1 1/2 hours straight. Then the vac drive belt started coming off. Put it back on three times and it came right off again. Anyone else have this problem? Is it cause the belt gets hot and stretches? How do you fix it?