I'm having oil pressure problems on my one Gravely 2 wheel tractor that is driving me to drink. What I did was this, since the this tractor had the old style oil filter you can't buy anymore, I robbed the head from another that has the replacable filter on it. This head also had the gauge on it. I hooked this all up then found I had to rob the relief valve body so the tube would reach. [The other one was too short] Got the tractor running and realized the oil pressure wasn't what it should be. As matter of fact, sometimes when I started it, there was no pressure at all. I figured that maybe the pickup tube inside was the problem. Drained the oil, took off both axles, [Did I mention that those gear reduction wheels are heavy suckers?], cleaned the pickup tube screen, cleaned all the slim from the bottom, made sure the tube was clear, put it back together and fired it up. Well, the pressure was a little better, but the needle only went to the high part of the low pressure area, right between low and normal. I decided I would take it out and run it a little to see what happens. After running it for a while under a load using the sickle bar mower, the engine got hot and the pressure went down to almost nothing. This was last weekend. Discouraged, I put it aside and went to work on John Deere LA. Today, I took off the lines and made sure everything was clear by blowing air through them. All was well with the lines. I checked the gears on the oil pump and they seem fine, but still have low oil pressure. The engine has real good compression and doesn't smoke. I'm out of ideas and quite frustrated. Does any one have any ideas for me to try? Is it possible that it is an older engine and doesn't provide enough oil pressure for this setup? I would like to get this tractor running properly because it has the gear reduction wheels on it and I can use the rotary plow on it. One more thing I should mention in case it matters, the valve relief body has the spring and ball in it.