ok i have an old swisher big mow, with an 8hp briggs. its the 2 speed one. i mowed with it just a couple times and some putsing around the yard, and then the drive pulley that attaches to the gearbox shaft seems to be spinning on that shaft!!! it has a set screw but no matter how hard its tightened it still gets loose then spins on the shaft again. there is a flat spot on the gearbox shaft and you would think there would be a flat side on the inside of that pulley to match the flat spot on the gearbox shaft but it isn't, its round. any help would be greatly appreciated thanks!