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  1. #1
    New Member
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    Mar 2014
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    Fond du Lac, WI
    Tractor
    Ford 8N

    Default Frustrating Oil Pressure Issue

    Hello,

    I am obviously new to this forum hopefully a few of you take the time to read this post. Thanks in advance. I have a few old 8Ns and one is currently on its way back together after a bit of a resortation. For engine work, I did not do a complete rebuild, I did rings and rod and main bearings using the same size bearings as original. I also checked tolerances with plastigauge and it seemed to be ok (I think I did it correctly... not sure).

    The problem is low oil pressure... nearly 40psi upon cold startup with 40w oil. Within 10 minutes of running the pressure was down to about 10psi with a wonderful engine knocking noise. I then replaced the oil pressure relief spring and plunger for an increase in oil pressure to nearly 50psi at cold start up then dropping to just below 20psi with in 10 minutes of running. So I gained a few psi but the knocking noise is still noticeable even at about 18psi. I am very frustrated because the plasti gauge tells me tolerances are ok.

    I will be pulling the oil pump to rebuild it which I should have done right away. I hope to gain another 10psi. But my main concern is the knock noise. Is there anything I can do to mitigate the problem? Next size up for bearing shells?

    By the way, anything above 18-20psi, the engine is very quiet and runs great.

    Thanks for any input!

  2. #2
    Gold Member 8N Ren's Avatar
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    Apr 2013
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    305
    Location
    Manitoba, Canada
    Tractor
    8N Ford

    Default Re: Frustrating Oil Pressure Issue

    18 PSI on a warm 8N isn't a problem, it's braggin' rights.
    As for the knocking, where's it coming from???
    More info is needed.

  3. #3
    Bronze Member
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    69

    Default Re: Frustrating Oil Pressure Issue

    I don't know why but a lot of folks tend to forget the cam bearings when rebuilding an engine. These also need to be checked for clearance while the engine is torn down. If they are out of spec. you can easily be loosing oil pressure there.
    Does the knock tend to go away when the engine is under load or does it get louder?
    to the forum!

  4. #4
    New Member
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    Mar 2014
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    14
    Location
    Fond du Lac, WI
    Tractor
    Ford 8N

    Default Re: Frustrating Oil Pressure Issue

    Thank you. I will try to explain a little better. I can live with 18psi but its the knocking i'm concerned about...

    I have not yet been able to test the tractor under load, it is not completely back together yet.

    But the knocking seems to be coming from the front of the engine but I can't pin point it. And only when engine is warm and oil pressure drops below 20 psi. If I speed up the throttle, oil pressure goes to about 30-35 and the knocking goes away and it sounds great. But as soon as I bump the the throttle back down to idle speed, oil pressure drops to just under 20 (about 18 according to the guage which is brand new) and the knocking sound comes back.

    I did not do anything with the cam bearings mainly because I didn't have the time to get that far into the engine even though I should have.

    I think once I go back and rebuild the oil pump, oil pressure will be where it should be. But even if I don't hear the knocking noise, would it still be causing damage?

    Hopefully this helps. And thanks your help!

  5. #5
    New Member
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    Mar 2014
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    Location
    Fond du Lac, WI
    Tractor
    Ford 8N

    Default Re: Frustrating Oil Pressure Issue

    In other words... Had I rebuilt the oil pump before I ran the engine and had better oil pressure, I may never have noticed the knocking noise. Hmmmm...

  6. #6
    Bronze Member
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    Oct 2009
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    69

    Default Re: Frustrating Oil Pressure Issue

    I'm not that familiar with the internals of your engine. Off hand I would say that if the engine is quiet when under load for a couple of hours, just run it.
    Why rebuild the oil pump? Are they that expensive that replacing it with a new one is out of the question. When we used to rebuild a car engine it got a new oil pump no questions asked. Cheap piece of mind.

  7. #7
    Gold Member 8N Ren's Avatar
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    Apr 2013
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    305
    Location
    Manitoba, Canada
    Tractor
    8N Ford

    Default Re: Frustrating Oil Pressure Issue

    I don't think you need to be rebuilding the oil pump, I could be wrong and if I am Soundguy will correct me, but like I said before your pressure is fine. 10 PSI with a hot N motor idling is good.
    Maybe the water pump??? Mine knocked like that once upon a time.
    Can you smell coolant???
    Can you see evidence of coolant that has splashed on the motor or under the gas tank?
    Are you running your tractor on 6 volts with the genny???
    If so maybe it's the pulley, not an uncommon thing to happen as bearing wear out.

    Don't just go and throw money at it, troubleshoot what's going on, unless of course your rich, then throw your hearts content lol.
    Do yourself a favor if you haven't already and go check out yesterday's tractors, they have an entire forum dedicated to 2 9 and 8N's.

    And one more thing, with the tractor off, grab the fan and try to wiggle it, might be able to tell if the bearing is shot in the water pump.

  8. #8
    Epic Contributor Soundguy's Avatar
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    48,766
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    Central florida
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    ym1700, NH7610S, Ford 8N, 2N, NAA, 660, 850 x2, 541, 950, 941D, 951, 2000, 3000, 4000, 4600, 5000, 740, IH 'C' 'H', CUB, John Deere 'B', allis 'G', case VAC

    Default Re: Frustrating Oil Pressure Issue

    6psi per 1000 rpm is minimum needed pressure.

    18 psi on an N is plenty.. she's worn.. but plenty.

    knocking noise.

    gig you have the head or block milled?
    souNdguy

    sent from my NOKIA LUMIA

  9. #9
    Epic Contributor Soundguy's Avatar
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    Mar 2002
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    48,766
    Location
    Central florida
    Tractor
    ym1700, NH7610S, Ford 8N, 2N, NAA, 660, 850 x2, 541, 950, 941D, 951, 2000, 3000, 4000, 4600, 5000, 740, IH 'C' 'H', CUB, John Deere 'B', allis 'G', case VAC

    Default Re: Frustrating Oil Pressure Issue

    Quote Originally Posted by Cvans View Post
    I don't know why but a lot of folks tend to forget the cam bearings when rebuilding an engine. These also need to be checked for clearance while the engine is torn down. If they are out of spec. you can easily be loosing oil pressure there.
    Does the knock tend to go away when the engine is under load or does it get louder?
    to the forum!
    giving advice on an engine you are unfamiliar with is counter productive.

    you will look a looooong time to find cam bearings in a N engine.. .. because ford didn't put cam bearings in!

    the cam runs bare int he parent bore.

    you CAN custom machine for cam inserts however...

    if I was the OP.. and I did not mill the head or deck.. id drop the pan and look at main and rod shells.

    first i'd kill 1 cyl at a time and see if the knock is on a cyl ( rod ).. or not
    souNdguy

    sent from my NOKIA LUMIA

  10. #10
    Veteran Member
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    N. Yarmouth, Me.
    Tractor
    N. Holland tc30

    Default Re: Frustrating Oil Pressure Issue

    Knock with no load?

    Loose front pulley? Worn thrust bearings? Sticky piston pin?

    Knock sounds like what?
    Coming from the upper or lower end?

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