Why does my belt want to run off my expandable wheel?

Make sure you are running at the motor RPM 1725. Check the diameters of both pulleys they should be matched. For example, a 2" and a 2" (basically 1:1). If you have a stepped pulley on the arbor, match as close as you can to the motor pulley. Make sure the Drum is mounted properly, the slots should be opening when you start it. Never run it without a belt. Feel the drum and make sure the rubber is still soft and pliable.