I bought an old belt-driven air compressor from craigslist, and I'm having difficulty keeping the belt on the tracks. The pully doesn't have a single deep valley like most compressor's I've seen, but instead has several fine grooves/channels and the belt has treads to match. When I brought it home I noticed that the belt wasn't seated in the grooves, so I loosened the motor and reseated it. Apparently, the previous owner had left it running like that for a while since there are wear marks in the pulley where the belt was previously sitting.

After I reseated it, I started it back up and the belt jumped off the tracks again. I'm thinking this is an alignment issue, but there is no way for me to adjust it as everything bolts in to factory holes. The other thing I'm wondering if maybe I just need to get it really tight.

 

Check the alignment of the pulleys with each other using a straight edge. If the straight edge doesn't hit all four points on the pulleys, one is out of adjustment and should be moved in or out on the shaft. Also check your motor mount to ensure the motor shaft is parallel to the compressor shaft. If it is askew, it can cause the belt to jump. Let us know how it goes..

 

Sure enough, it was belt alignment. Once I was able to free up the pulley on the motor, I was able to get everything more or less parallel, and it hasn't slipped off.