Go back to the basics...
If the valves are now opening then check to see if you have air moving into the intake and out the exhaust. An engine works like an air compressor If the valves are opening Turn the motor by hand and make sure the intake is opening on a down stroke and the exhaust is on an upstroke ( can pull a injector and or a glow plug to check that). Are you getting bubbles in the radiator? Is the head gasket leaking? I am going to assume that when you had the head off the cylinders looked good that there were not any gouges or deep scratches going up-down that could indicate a problem with the rings.
Another thing you can do squirt a small amount of motor oil in the cylinder then hook up the compression gauge to see if that changes the reading. If it does you have bad rings.
The forum member we all respect, North Idaho Wolfman, has advised against this oil in cylinder practice:
From memory, his concern is that the volume of head and piston in these diesels is so small at TDC that you risk hydro locking the cylinder and bending or breaking very expensive parts destroying the engine.
I have a feeling there are some important chapters in this tractor's story which are missing.
You do not go from having sufficient compression to run, park for two weeks and then the compression is now zero.
Dave
