I was doing some road work, after a few hours, the engine developed a knock around #1 cylinder. I would have bet it was a rod knock. 20 year old engine rebuild with around 500 hours on rebuild. Parked the tractor, dropped the pan and pulled the head. No metal in the pan, no marks on the head or pistons. Rod and main caps are tight. Have not checked rod and main bearings yet. Rotate engine by hand, rotates smoothly. Water pump, front pully, timing gears all tight. No place in crank or cam. There is some discoloration in the red paint front left corner of head and block, like it got hot, but temp gauge was normal. I have read about sleeves coming loose but when I was turning the engine by hand, sleeves don't move. But that could be because the engine is cold, could move when hot.
I'm out of ideas.
I'm out of ideas.