After a couple hours moving gravel and grading on a hot day, I noticed my oil pressure had dropped to 35 psi. Time to adjust the oil pressure.
Looks easy in the service manual. What it doesn't say is that the relief valve adjusting screw is behind the left cylinder about 5" in from the cylinder head cover in a space about 3" wide. There is not enough room for my big hands to fit in this small space. You can loosen the jam nut from the block with a 5/8" socket and extension. The problem is, the jam nut is just that, a jam nut. It holds firmly onto the adjusting screw and makes it difficult to turn the screw inside the nut even when its loose from the block.. No room for a conventional box end in this tight space. The adjusting screw takes a 7/16" Allen wrench.
To make things more difficult, my tractor has a model 20 loader. The front support tube and loader frame are pretty much in the way. To solve the problem, I heated and bent a 5/8" combination wrench 90° near the box end. The Allen wrench issue is not a problem if if you have a 3/8" drive set of Allen sockets, extension and ratchet. I don't see any way a conventional Allen wrench would work. By clamping a set of vice grips on the open end of the bent combination wrench, you can hold the jam nut while applying enough force to the adjusting screw to turn it inside the nut. You have to adjust it in stages, loosen nut, turn in the screw a half thread, snug the nut, start the tractor. If pressure is still too low, repeat the process until it gets high enough...40-50 psi while idling at operating temperature. Then tighten the nut securely against the block.
Just to add to the confusion, the tractor side cover wouldn't clear the loader support tube. It took a lot of twisting, turning and lost paint to get it out. I'll have to modify it slightly to get it back in more easily and repaint the affected areas.