Are you supposed to change the belt at a certain number of miles or just change it if it breaks? What are signs that it's worn?

 

To inspect it you can look for "glazed" spots, this would indicate you burning the belt. You should look for dry cracks when you bend the belt exessively, if cracked, replace it. There also is a wear factor. On the side of the belt, there is a minimum thickness, which I am unsure of this measurement. I am confident someone here will chime in with the measurement!