need help on 4020 John Deere

My father has been working on this one a couple of days and it is whipping both of us.The tractor is a diesel and the problem is there is no oil coming out of the rocker arms to lube them.This tractor sat a while but the engine runs great and has good oil pressure. The oil pressure was running around 30-35 on idle but there is absolutely no oil coming out to lube the rockers.We have taken the shaft off several times and it is completely clean inside.You can easily blow through it with air.The roll pin that locates the shaft to the head is good and the oil hole lines up with the head just as it should.With the rocker shaft off you can turn the starter to build the oil pressure up to 30 but only a trickle or small pulse tries to come out of the head.Is there a check valve somewhere in the block that regulates the oil to the rocker shaft? We are both VERY competent diesel mechanics but this one has us whipped and we are at the point of tearing into the motor to try to find the problem.ANY help would be greatly appreciated.

HaleyHas the head been off lately?Gasket turned end for end or not correct?Or it could be a spun rear cam bearing as it oils the rocker shaft from the rear cam bearing.

Not knowing the engine, but with a formerly useful idea!
If the passage from the hole in the rocker shaft support in the head is a straight drilling to the cam bearing (probable), the use of a thin brazing rod to probe down the hole,while very slowly turning the engine by hand, will allow you to feel the cam journal aligning with the hole. If it will not "find" the hole, expect a spun, or improperly installed cam bearing.
You could also blow air down the hole and listen for a change in flow when the holes line up. Jim

Look at the ends of the rocker shaft, are the rubber plugs right against the cotter pins? Had a 4020 that the rubber plugs got hard and moved into the shaft tube and cut off the oil to the shaft. But it does sound like the problem is deeper. The brazing rod trick that Janicholson mentioned won't work unless the head is off. Also the oil gallery for the sender, rear main, and rear cam bearing all are off of the same passage if memory is right. And no check valve for that port. chris

I would take the rocker arm shaft off and then blow compressed air down through the oil port. Then listen to the air flow. I have seen spun cam bearings cause this. I also have seen a chunk of dirt/carbon plug the port. Where using parts cleaner and compressed air will some times clear the passage way.

Has the rocker arm assembly been taken apart??? The rear rocker arm support is the only one drilled to allow the oil to flow up around it. If someone put the wrong support in the rear then you would not be getting any oil up to the rocker arm shaft.

There is not a check valve or anything else like that in this engine.

The oil comes up from the oil pump and then up through the oil cooler. Then down the line from the top of the oil cooler to the oil pressure rail/galley that runs the length of the motor on the right side. Then the block has passage ways to each cam bearing. Then the oil on all of the cam bearings but the back and front go to the main bearing only. The front passage goes to the main bearing but also on across to where the ventilator pump is on the older engines. The rear passage way goes to the main bearing and the internal passage way up to the rocker arm assembly. I just happened to have the JD 4000 series manual laying on my desk. LOL

Another thing I have done is drain all the engine oil. Put two quarts of new engine oil in then fill the motor up the rest of the way with diesel fuel. Start the motor and run it at low idle until it comes up to operating temperature. Drain the mix out and see how much dirt you get out of the block. If you have a plugged port this may clean it out.

If none of this helps than you have an internal failure. More than likely a spun cam bearing.

Thanks for all the comments and ideas.You guys may be on to something with a spun cam bearing.We have tried blowing air back down through the oil hole for the rocker shaft and hardly any goes through. We have also tried blowing air through the oil galley plug just to the rear of the tach drive and none comes out the top.We also tried shimming the oil pressure spring to 100 psi idling and still no oil goes up top.We did notice that when you spin the starter with the rocker shaft off the little bit of oil(very little) that does come out the rocker shaft hole has a distinct pulse to it instead of a steady stream like the oil galley plug closer to the bottom.How common is it for these engines to spin a cam bearing? We have worked on literally hundreds of engines over the years and have never seen one with a spun cam bearing.If it turns out to be a spun cam bearing it will be a first for us.

If you are luky ,I think jd has the rite idea , I would look hard at those rocker arm supports,make sure the correct passage bolt is in the correct spot ,. just did valve job on Pops case 188 /430,,. it oils from back pedestal but another 188 I workt on 5yrs ago oils from the front pedestal,Naturally I put Pops together Basackwards and was stumped and concerned when it did not oil, just like you are.. ///.. if you choose to flush the motor as JD suggests,,. that ought to do it ,and remove all doubt and probably everthing else too fast ... if indeed that solves the problem ,.then you are home free ..?kinda? , you have done the best method I would suggest ,, BUT , you are dealing with a filthy engine ,I would suggest lite duty , til she cleans up ..,watch your oil pressure guage and change oils and filter early ,. the diesel fuel could loosen too much crud and foul up the works ,. add about 3 pints of atf to the oil to slowly loosen that crude down and capture it in the filter .case in point ,. ,,. about 10 yrs ago i pikt up a cheap 86 Celebrity ,,. good running v-6, terribly gunky inside , had about 150 thousand miles ,, I put a can of seafoam in the oil,. they state on the can it will clean the engine up inside ,, I think it was too aggressive ,my best guess is that it took up some gunk and plugged a journal , bottom line , it spun a bearing

The oil passage in the cam journal aligns with the cam bearing hole only once per cam revolution (1;2 crank shaft speed). Very poor odds that it stops at that point. You need to rotate the engine slowly to find the alignment (not a mark to turn to) Jim

So what you are saying is that the cam bearing does not have a groove on the inside to let oil flow continuously around the journal? We actually rigged up an air hose to blow continuously into the lower oil galley plug by the tach drive yesterday.We then turned the motor extremely slow and at one point in the circle air blew out the rocker shaft oil hole up top just like it should.My father is convinced now that the rear cam bearing is spinning in the block but if what you say is true that may not be the case.If you are right this brings us right back to square one and out of ideas.