I have a 2654 Husqvarna and my daughter jammed a stick between the 2 back transmission pulleys. It only has about 50 hours and about 9 mths old but the belt will not stay on now. Can it be a pulley or the belt? It isn't making any noise but as soon as you put it in reverse it comes off. Is the belt usually tight? How can I tighten the belt tensioner?