tom, did you check to see if the oil pressure  relief valve was free? on the right side of the engine near the timing cover, but in the block is a plug that takes a 13/16 wrench to remove. there should be a spring and a plunger in there. remove the spring and plunger and clean them, it wouldn't hurt to stretch the spring a little. sometimes it is difficult to get the plunger out, if you start the tractor it may blow it out. let me know how you make out, chuck