I have a Ferris IS 3100 Z that the drive pulley keeps falling off. Any tips on keeping it from happening. Installation tips? I think it may have something to do with how I put it back together. A friend of mine thinks I'm running out of threads to compress it on the shaft. There is room for 1/8" of thread space in the upper pulley when it falls off and bolts are snugged tight. Torque values on bolts? I have them pretty tight, by feel I'd guess close to 100 ft/lbs. If you haven't seen one of these, the pulley is two pieces. the inner one is pulled into the outer one by the bolts and one is tapered which compresses the inner one onto the shaft. Dealer didn't have any ideas.