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8N lost oil pressure again

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FLAcharlie

09-03-2004 03:54:13

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I'd lost oil pressure, and did the "squirt oil in thru the oil pressure relief valve hole" thing, and it was OK for a week after that, but it needed some other things done, so I had my tractor guy overhaul the oil pump parts. He got it all back together again yesterday, and called to tell me it ran fine for about 10 minutes before it lost all oil pressure again. Besides another oil pump failure (possible I suppose), or that tube the oil gets sucked up having some problem, any other ideas what to check ?

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OK-AL

09-03-2004 14:32:35

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Re: 8N lost oil pressure again in reply to FLAcharlie, 09-03-2004 03:54:13

Go over to the 8N forum and do a search on oil pressure. This is a very common problem with 8N's. I had the same problem. It was a loose oil pickup tube. No, it didn't move when you lightly pushed on it, but it did move if you pushed harder. The weld was broken where the tube entered the oil pump. That's what I would guess your problem may be. The oil pump housing may be expanding more than the tube as it warms up.

If that's not it, then did your oil pump housing could be worn out or the bushing in the housing could be bad, allowing the shaft to move.

What did the front main bearing look like when you pulled it? I assume you pulled it because the oil pump is part of the front main bearing housing. Did the main bearing show excessive wear? If you have to pull it again, check the main bearing clearance with plastigauge. Also, pull some rod bearings and check them, too. It's very posssible to have bad bearings but good compression.

Let us know what you find out.

OK-AL

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FLAcharlie

09-24-2004 17:29:56

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Re: 8N lost oil pressure again in reply to OK-AL, 09-03-2004 14:32:35

FINALLY, have an answer. Turned out there was a hairline crack in the oil pump BODY (expensive). While it was all apart replaced a lot inside, like bearings etc.. Compression tests were all excellent so no work on pistons/rings etc.. Also discovered it"s an April "49 unit, couldn"t tell before... So, hope it"s OK for another 55 years or so...

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RAB

09-03-2004 09:46:25

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Re: 8N lost oil pressure again in reply to FLAcharlie, 09-03-2004 03:54:13

What about the pressure relief valve? Could that be where your internal leak is?
Regards, RAB

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FLAcharlie

09-03-2004 11:48:24

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Re: 8N lost oil pressure again in reply to RAB, 09-03-2004 09:46:25

hmmm. since the first thing we try is to remove the oil pressure relief valve and squirt some oil down there, to try to "re-prime" it, I think we'd notice a busted spring or something, but it is one more failure point to double check, thanks.

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RAB

09-03-2004 14:12:38

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Re: 8N lost oil pressure again in reply to FLAcharlie, 09-03-2004 11:48:24

You don"t need a busted spring - just some crap sticking to the seat or just a poor seat - especially if you are on "cheap" oil or an oil pump with tolerances at the limits along with your bearing tolerances a bit on the wide side.
RAB

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Allan in NE

09-03-2004 04:11:12

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Re: 8N lost oil pressure again in reply to FLAcharlie, 09-03-2004 03:54:13

Hi Charlie,

How satisfied are you with the condition of your engine bearings?

Sounds to me like the oil is getting hot(10 minutes), thinning out and then the pressure drops.

Something to think about,

Allan

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FLAcharlie

09-03-2004 04:19:32

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Re: 8N lost oil pressure again in reply to Allan in NE, 09-03-2004 04:11:12

we think the bearings are OK, in fact in very good shape. Before the oil pump overhaul, when first started, oil pressure was like 50, then for the first hour about 22, and after that it would bottom out around 18. wasn"t really burning any oil either, maybe 1/2 quart every 15 hour operating. Before the oil pump overhaul, it had sat for 4 or 5 days, and when started, oil pressure was zero from the get-go. As I said, squirting oil thru the oil pressure relief valve hole brought oil pressure back to normal behavior, and even after sitting for a week it was still OK. My tractor guy also reports that the gears from the pump were indeed worn badly. Also did a compression test and that was fine all around, though has nothing to do with this problem. Anyway, right now my sense is either some problem with the newly installed parts, or that oil pickup tube has a problem, but all ideas are very welcome, thanx !

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Allan in NE

09-03-2004 04:30:13

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Re: 8N lost oil pressure again in reply to FLAcharlie, 09-03-2004 04:19:32

Charlie,

Sure hope you get 'er figured out and going again.

I was just trying to help, as that "good oil pressure when cold & low when hot" symptom just screams of excessive bearing clearances.

Allan

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TheRealRon

09-03-2004 04:01:40

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Re: 8N lost oil pressure again in reply to FLAcharlie, 09-03-2004 03:54:13

Any leak, no matter how tiny, in the pickup tube will cause the pump to suck air and lose its prime. A much more remote possibility is that the pickup is loose and or defective and is laying directly on the bottom of the pan. This starves the pump.

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