My Mini Z 52" with 160 hours on it threw the blade belt off of the idler pully today when I engaged the PTO. I have felt for about a week now, that the blades might have been slipping a bit. I remounted the belt and adjusted the idler adjustment chain one link tighter. I know all belts stretch a bit . Is this considered a normal wear adjustment ?. All pulleys are free turning and not binding. I will get a new belt tommrow. thanks for any advice.