I have a Skil Belt
Seven years later... sorry, man!— Solution — I have a Skil Belt Sander model 7313 which must be very similar if not the same. It has a 3/4HP motor, 3" x 18" belt capacity, a lever for belt release and a single Phillips screw for "adjusting auto-track" which is a misnomer in itself. Very odd. That screw is on the front left as you are using the sander, belt-down. When you "loosen" (CCW) this screw, the belt should move (if at all) toward the body of the sander; "tightening" it (CW) changes the angle of the front roller, which can force the belt off the open side. In my case I had to loosen it all the way just to slow it from slipping off the machine.My tolerances wore over time — or my belts were constructed poorly — so that the belt always rode off and away from the machine no matter where that screw was .So, I "shimmed" the roller closest to the adjustment with a 1/2" strip of duct tape one full wrap around (this made the end of the roller closest to the tracking adjustment "fatter." Tested it. It needed more. I added another piece of tape to the complete circumference of the roller, but this time 1" wide, covering the first tape right up to to the original edge, and over toward the middle. Tested it again. It needed more, but was improved. I added one more tape, 1-1/4" wide from the same edge out to the middle — effectively making a bit of a 'cone' toward the center, and this solved it for me. I think that in my case, the belts I bought at Home Depot were just a bit too long and needed this shimming method to take up slack. I found it easiest to make final adjustments "under load." Sand something right-handed using light pressure and adjust the screw with your left hand. (Note: this differs from the offical instructions in the manual: https://www.manualslib.com/manual/132374/Skil-7313.html?page=8.It may help to lubricate the pivot point of the front roller, which is actually about 4" back of the axel, right at the release lever's rivet, back inside the machine. If this pivot point is not fee moving, your auto adjust may not be able to allow proper rocking for adjustment.Also, with the belt off the machine, you can get a better idea of how the adjusting screw for the so-called auto-track feature does its work. Mine seems to have a lot of room to adjust it exactly the wrong direction, and no adjustment in the opposite direction. Hence my shimming idea.