Thats a thought, I removed the injectors without pulling out the push rods but I'll check them when I go back in. The timing gears look good. I checked the key on the cam but not the crank, really don't see how a key could be partly sheared.
The tractor was running fine, except for a little black smoke, then it started loosing power and backfiring almost didn't make it back to the barn. So far I haven't gotten inside the engine just the valve cover and timing gear cover. I think the camshaft may have to come out. Ever heard of camshaft breaking or some other disaster happening to it? Also I can turn the engine CCW with a wrench but not reverse. I don't remember if that was the case when I overhauled the engine about 20 years ago.