I own a model 917.275685 lawn tractor. lately I have noticed that if I shut off the pto after a bit of mowing to cross an obstacle it will not engage again. I was surprised to find that it worked again later after everything cooled down. I tested it by doing the same thing. mow for a bit and shut off the pto then try to re-engage. same thing. I have checked the clearance with a feeler gauge and its about 12-13 thousandths. before replacing it outright I though I would check here and see if there are any pearls of wisdom. if replacement is the answer how is the best way to stop the engine from turning when I try to turn the main bolt on the clutch? Thanks in advance for the help.