You will need to check for 12V and ground at the harness for starters. AN increased gap will not always let a clutch engage, but would it pop the fuse getting hot enough? Never say never. Is it possible a wire backed up in the connector behind the pto switch?

I'll try to explain as best I can. The "PTO" I'm referring to is the front pulley that the belt coming from the mowing deck wraps around. This is the pulley that transmits the power from the engine to the mowing deck. It is at the front of the tractor beneath the engine. If you grab it and try to rotate the pulley it should barely move. Mine was moving about half a turn, the only thing stopping it was the wire coming from the wiring harness. The rod fits into a hole on the top of the pulley. If you are standing in front of the tractor facing the engine, the rod and hole are on the left side of the pulley. If you can raise the front of the tractor, you can get enough leverage to move the rod back into place. Try to bend the rod a little so there is a tighter fit and hopefully it won't pop out again. Or call sears and they will come out and fix for $150 Hope this helps

Think Timing... For power to be developed, the ignition of the compressed air/fuel mixture must take place at exactly the correct instant - just before the piston reaches Top Dead Center (TDC) on the compression stroke. Timing is set on older mowers with point type ignition systems by adjusting the point gap and generally only changes due to wear. However, these changes are gradual and unless the points come loose for some reason, will not likely suddenly prevent the mower from starting. On newer electronic ignition systems, there is basically no adjustment as the position of the electronic ignition coil/module fully determines ignition timing and this is fixed. However, timing can be grossly messed up if the flywheel key gets sheared and the flywheel then rotates a fraction of a turn on its mount on the crankshaft. The result may be a mower that does not start, backfires or runs erratically, lacks power, won't run and/or start when hot, etc. This is very likely to happen should the blade strike a rigid object causing the mower to stop instantly. In this case one or both of the blade lock key and flywheel key have sheared to (hopefully) protect the very expensive internal parts from damage. There are likely not going to be any timing marks for that old timing light you have sitting gathering dust somewhere. The only test really is to inspect the flywheel keyway to determine if damage has occurred.

You could try- with the engine off of course, pulling sideways on the pto belt and seeing if the idler cam goes back into position. At least that way you are mowing today.If not, drop the deck- 5 pins plus the linkage pin, and have a look. This can be binding on the top from rust or debris, the idler cam beeing worn where the brake arm rollers make contact or damaged brake arms. For this vintage, you want to confirm that the area where the top plate is welded to the rear of the deck is still solid. Tell tale signs that it is not would be notable wear on the top of the brake arm wher the spindle pulley had made contact from the plate being pulled up when the deck wa s engaged.