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Oil Pressure problem-John Deere

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Jim Ghormley

04-08-2005 10:01:50




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I have a 1939 John Deere Model L with a Hercules NXB engine. I rebuilt it and checked all the clearances which were within tolerance. It only has 2 PSI of oil pressure. I can take out the gauge and blow out the line with compressed air and the oil pressure will go up to about 25 PSI, which is normal when I start it again but within 5 minutes it has slowly dropped back to about 2 PSI. I have already checked the gauge. Any ideas on how to fix it without tearing it all apart again to replace the oil pump? And where can I get a new oil pump?
thanks, Jim

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buickanddeere

04-09-2005 10:01:43




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 Re: Oil Pressure problem-John Deere in reply to Jim Ghormley, 04-08-2005 10:01:50  
Can you close off that oil pressure relief passage 100% and check the oil pressure? This should narrow down the possibilities.



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Jim Ghormley

04-09-2005 10:26:42




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 Re: Oil Pressure problem-John Deere in reply to buickanddeere, 04-09-2005 10:01:43  
I will try to close off the oil pressure adjusting valve as much as possible. It has a spring and a small little piston looking valve at the end of the spring that is about 1/2" x 1/2" in diameter. I will cut a small piece of pipe to put between the spring and the valve to increase the tension of the spring on it. I think I want to also try in a different test to fill up the crankcase with more oil to see if there is a problem with the oil flowing back into the crankcase. I am still wondering if something isn't caught or stuck in an oil passage or in the screened in pickup tube connected to the oil pump. I wasn't able to get into the screen covered looking hockey puck size pickup for the pump and clean it really well. It looked fine but maybe there was some junk in it that I didn't see. Jim

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DRL

04-08-2005 20:53:28




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 Re: Oil Pressure problem-John Deere in reply to Jim Ghormley, 04-08-2005 10:01:50  
What brand of oil filter do you have in it? Some aftermarket filters do not allow enough flow for these type of engines. Would start there. Install a John Deere filter and see what happens. If this doesn't help, would bite the bullet and pull the pan or whatever you need to do to get to the pressure relief valve. Look at your parts book or a blow up of the valve and be sure that all the washers and springs associated with it are still there. Then see if the springs are within tolerances. If nothing else helps, would still spend the money on a gasket set and open it up again and see what is the problem. Carb cleaner and the such is going to be hard on seals and gaskets and not going to get the job done. Well worth the cost of a gasket set to fix it right. A lot less expensive than having to redo the motor because of ruined bearings.

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Jim Ghormley

04-09-2005 07:16:28




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 Re: Oil Pressure problem-John Deere in reply to DRL, 04-08-2005 20:53:28  
This is a 39 Model L with a hercules engine. It doesn't have an oil filter and you can't just drop the pan. You have to pull all the sheet metal back off and pull the entire engine and take off the bell housing to get the oil pan off. That is why I am trying to avoid it. The oil pressure adjustment valve is on the top of the engine and I have had it out and tried a number of different settings with it. I will try and put a spacer in between the spring and the small piston on the end to see if maybe the spring doesn't put enough pressure on it. Any more ideas???
Jim

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Hermit

04-08-2005 19:09:44




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 Re: Oil Pressure problem-John Deere in reply to Jim Ghormley, 04-08-2005 10:01:50  
Possible oil filter problems? Not seated properly. Changed to a new free flow type. If this is the reuseable type, both elements assembled and seated properly.



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Jerry/MT

04-08-2005 17:37:01




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 Re: Oil Pressure problem-John Deere in reply to Jim Ghormley, 04-08-2005 10:01:50  
Sounds like a pressure relief valve is sticking open.



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1945 Ar

04-08-2005 13:06:36




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 Re: Oil Pressure problem-John Deere in reply to Jim Ghormley, 04-08-2005 10:01:50  
Don't know anything about the particulars of your engine, but wondering, if it's possible the oil isn't draining back to the sump fast enough (plugged return passage/s)----
Just a thought....



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Allan in NE

04-08-2005 11:14:49




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 Re: Oil Pressure problem-John Deere in reply to Jim Ghormley, 04-08-2005 10:01:50  
Jim,

Does the oil pressure climb back up when you speed the engine?

I had a machinist leave out a plug on an oil gallery one time, and that is the way it acted.

Dunno,

Allan



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Jim Ghormley

04-08-2005 11:24:25




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 Re: Oil Pressure problem-John Deere in reply to Allan in NE, 04-08-2005 11:14:49  
I have already played with the oil pressure adjustment screw and removed it and blew this passage out. I have drained the oil and sprayed an entire can of carburetor cleaner down this hole and the gauge hole followed by compressed air till it came out the oil drain plug thinking some junk may be stuck in the oil pump line somewhere or in the screen. I rebuilt the engine myself and did not take out any oil plugs or even see any. The oil pressure goes up slightly with RPM but not near enough to where it should be. It still puzzles me why the oil pressure would be good for 5 minutes then slowly go down. When I first started the engine after rebuilding it, it had good oil pressure for 5 min. I have changed the oil 3 times.
Jim


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Allan in NE

04-08-2005 11:57:44




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 Re: Oil Pressure problem-John Deere in reply to Jim Ghormley, 04-08-2005 11:24:25  
Jim,

Not trying to be an alarmist, but when you say the bearings where "within tolerance", what kinds of clearances did you have anyway?

Good oil pressure cold, followed with it dropping when hot, just screams bad bearings.

Just tryin' to help,

Allan



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Mike M

04-08-2005 18:42:16




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 Re: Oil Pressure problem-John Deere in reply to Allan in NE, 04-08-2005 11:57:44  
Or bad oil pump.



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Jim Ghormley

04-08-2005 13:32:40




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 Re: Oil Pressure problem-John Deere in reply to Allan in NE, 04-08-2005 11:57:44  
That is a good thought about the return oil passages being clogged. Should I overfill the crankcase with oil to test it to see if I get some good oil pressure? If that works then do I drain the oil and fill the whole crankcase and all the engine up with carburetor cleaner and leave it set for a while? I am trying to avoid tearing the whole thing down again. I had the rod bearings rebabbited and honed the cylinders and put new rings in it. We checked all the engine tolerances as shown in the hercules engine manual and checked the rod and main bearings with plastigauge and they were within the tolerances specified in the manual.
Jim

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Weirsdale George

04-08-2005 10:38:13




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 Re: Oil Pressure problem-John Deere in reply to Jim Ghormley, 04-08-2005 10:01:50  
Don't know the particulars of that engine, but I would check to see if there is a pressure relief valve that might be sticking or leaking.



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