I have a 5 year old Ariens 13hp. I had a phone book jammed in chute stopped it dead! Since then, Drive belt comes off now and then. Could belt be stretched seems odd if it could? I see pully not lined up with idler but is when engaed. Comes off when I let go of drive system as I see it is angled? Need help???? Is there a distance pully should be away from other pully idler?