190xt Engine Oil Pressure issue

Decent oil pressure when cold and drops when warmed up indicates a worn out oil pump (doubtful) or worn main and rod bearings (probable).  I'm guessing .003" is a good bearing clearance, but I'm not looking at the service manual.

We pulled the plunger out. We weren't really sure what it should look like, but it did seem like it might be seating unevenly. There's a local guy that might let me pull his to compare and he might have a different oil pump to try. It looks like we are pointing towards a rebuild though. When we did the plasti-gauge i didn't think about the motor orientation being a factor, but I could see it. We were really hoping that an injection pump was all this tractor was going to need. Thanks for the help

Back in the 70's the factory fill was straight 30w Shell Rotella.

to me if it were worn bearings, it would not have good oil press ever. 

It really doesn't have good oil pressure when cold. With the pressure regulator bottomed out, I would xpect to see 75 or 80 psi for the first few minutes and gradually fall as it warms up.  Spec is 35 psi (hot) to 55 psi (cold) wide open throttle.

when you plasti gauged  the bearings out was there any copper showing? if there was i would change all main and rod bearings, and  slide in all new bearings.  Better yet pull the crank out and get it ground new bearings and resize the rods. I  slipped in new bearings  with my d-19 diesel and it helped alot without grinding the crank, my crank was not badly oblong on the journals.  you could also see how much play is in your rocker arms /shaft and if those corks are still there doing their job. you could run it wth the valve cover off and see how much oil is leaking out of the rocker arm/shaft. each worn part looses more pressure.  I like the idea of air pressure. you loose pressure as the oil heats up. your oil pump spring might also be worn out. your air pressure will tell u what psi the pump will bypass at.

You've got bigger issues than rocker arm shaft corks.

I finally had some time to work on this again. I pulled the valve cover off and found a bent pushrod. I replaced it, reset the lash and started the engine up without the cover on to watch it for a while. Oil pressure behaved the same. As far as I could tell, everything else in the valvetrain was functioning as it should. I am now to the point of an overhaul. Is there anything else I should look into/replace while I'm in this far?

Another thing to look at is to see if the engine has rods that have the piston cooling jets along with the rod bearing with the holes for them. I have run into this problem before.

if you have too much bearing clearance  you will loose alot of oil pressure there and sometimes in the camshaft and the rockers too, it all adds up. Reliance power parts  RELIANCE (reliancepowerparts.com)  has a oil pump listed,  you could start there.  It depends if you want to keep the tractor you could replace the rod and main bearings paying attention if they are oversize or not. the crank can be oblong from wear so it may not fix the problem entirely, but if its it not too oblonq  should help the problem. 

I can't see the Reliance part without logging in so I applied to be a "dealer" and we'll see...

Dr allis and others will know. What is the deal about the galley plug in these engines for oil cooler VS non cooler? Have no idea if this could be in play. I just remember talk about it and even though this engine hasn't been converted one way or the other as far as we know it made me wonder. Seems like a huge pressure change for loose brgs but I'm no expert in that field.

Here is an image from the bore scope. It is hard to tell from the picture, but is there a seat there?? I'm not sure what it is supposed to look like.