Update to JD 755 challenges - 2 obstacles remain

[Moukie]

Hello to all......brief update to where i am. I got the front end all put together; basically with all new bearings seals, shafts, etc. I put it back on tractor and ran it on jack stands Sunday and everything appears to work as it should. No odd noises, or obvious tricks. Had a really hard time getting dope in the spindle fill ports; can easily understand why they could be overlooked or neglected. I think she is ready to run from the front end standpoint. Yes!

Now that gave me a compelling reason to get back on the engine to investigate the oil pressure issue. After several hours of work, i got pan bolts out and tonight i got pan off. Initial take is OK. I took off 3rd main cap away from oil pump; one slight groove, barely enough to feel with fingernail. Journal looked super. Measured with plastigage and came up with about .003". I don't have manual in front of me, but i believe initial spec is .0015, and replacement is suggested at .006"? Seems like i would not be having 10 psi at idle with only that much wear, but i am not an expert. Does that seem correct? Engine block and ambient temp is about 40F.
Next, on to the middle rod bearing. Same story, about .003" with plastigage. I believe same specs as main bearing clearances.

I was really hoping to find something very obvious, but i did not. Now the decision is whether i go ahead and install new rod bearings which i have. Should i order and put in new main bearings? Or, should i maybe pull engine and look elsewhere like oil pump?

Any advice you all can give is great. I am kind of in a conundrum at this point. Just checked manual and it states .001-.003 is ok; replace at .006. Now what? Pull more caps? Oil pump? How hard is it to remove oil pump, and does injection pump have to come off first? If yes, is that tough to re-install? Never done that before.

Thank you,
David in SC

 

[beenthere]

What does your service tech manual say for pulling the oil pump?

 

[Agvg]

Suppose you have checked the pressure valve for the oil pump? Are you lucky it's just a bad spring or adjustment. No cracks in the oil pickup?

 

[Moukie]

Oil pump is next to read about. I suspected bearings because the psi drops way low on hot engine, but psi is not good on cold engine either. I will look close at OP. Pickup tube is on and screen was not clogged.

Thank you for the feedback.

 

[Agvg]

Have you tried to measure clearance with a new bearing?

 

[Moukie]

I have not....got too late and too cold. I may do that tonight; let me read up today on oil pump removal and check procedures. Do you know if i can remove OP without removing engine?

 

[mike48130]

Like AGVG said check the oil pressure relief. Usually a spring with a steel ball or plunger. They can wear or get dirt in them and not seal properly. Also when you get it running, pull the valve cover. Sometimes there are oil galley plugs. Possibly one is leaking or fell out. I think if your oil pick up line had a leak, you would get foamy oil from the air.

 

[Moukie]

Thank you for all the feedback. Plan for tonight is to pull the main bearing farthest away from the oil pump; if it looks good like the one next to it, I will torque those two mains up and check one more rod bearing. I might go ahead and install the new rod bearings since I have them. I will plastigage them to verify clearances before I final torque them. I also intend to remove the pump pickup tube and verify 0-ring condition; screen and bottom of tube look to be ok. After all this, I think I need to pull oil filter and the spring/plunger assembly to check it out. If all that checks out OK, not sure what the next step would be.

Thank you so much for the advice. I am getting very excited about being able to use this machine. Should be in pretty good shape once I finish up all I am doing.

David in SC

 

[Moukie]

Good evening from rainy SC. Finally figured out the low oil psi issue. The other night, I pulled another rod and another main bearing. Plastigage shows .003", which is inside spec, and everything I could see looked to be in great shape. So, I pulled the oil filter pressure valve. Ah ha. Spec for the spring is 43.5 - 48.5 relaxed, and mine was 37mm. Had two 0.5mm shims, but still nowhere near long enough to get the proper psi. Manual stated I could add 1.6 psi for every one mm of shim added, but I could have only added about 2mm before I ran out of housing room. Even adding 3.2 psi would have only brought me to about 15 psi; not near where I wanted to be. So, two days and $82 later, I picked up my new pressure valve assembly today; JD would not only sell me a new spring. No problem; really a small price to pay for what I got. I torqued everything back up, cleaned up and painted oil pan, and started her up just before dark.. Wow, 56 psi! Unbelievable difference. Oh yeah, I went ahead and adjusted valves while I was in the area. Took longer to access valve cover than it did to remove oil pan.
I am tickled now. Have a working 4WD tractor with a super-strong engine. Now, I can get to using it and not have to worry about the oil pressure. So happy.

Thank you all so much for your help on this. I am sure there will be more, but for now I will likely use the tractor and quit pampering it.

I actually had this happen once before on a freshly built 8N. Maybe next time I will remember to check that before going much deeper.

Thank you all, and have a nice evening,
David in SC

 

[beenthere]

:thumbsup: :thumbsup:

Thanks for reporting back on the successful find/fix. Good info for the TBN archives and good for you to have the up-and-running tractor.