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  1. #1
    New Member
    Join Date
    Oct 2012
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    Location
    Jefferson City, MO.
    Tractor
    1947 8n Ford

    Default 8n-High oil pressure

    My 1947 8n worked fine on Sept. 22nd. Put it in the shed turned off gas let it run out. Got on it the next day and it was locked up. Took the starter out, was'nt that. Pulled it around trying to break it loose and nothing. So I put it back in the shed, pulled the plugs out they looked fine so I left them lay. Got back to the farm on Sept. 28th with intensions of taking the motor out (Which I had already located a used one) thought I would try to turn it over for whatever reason and now it turns over. So, I put the plugs back in, changed the oil, which looked good no shavings, turned the gas on and it fired right up however, the oil pressure is at 40+ at idle and pegs the gauge at half throttle. It's not making any noises or smoking. I only ran it for about 45 seconds. I did research this and came up with the pressure relief spring. Any help on this? What would have caused it to lock up then come unlocked and why the high oil pressure now? Thanks

  2. #2
    Epic Contributor Soundguy's Avatar
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    Mar 2002
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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: 8n-High oil pressure

    the lockup could have been hydraulic lock with fuel setting atop pistons.. then evaporated after you left plugs out.

    high pressures?

    i'd pull the relief plunger and inspect it make sure it is not sticking int he bore or somethng ood like that.

    go ahead and pull the oil gauge too.. when in doubt.. a new gauge is 10-15$..

    post back

    you really shouldn't see much over 45psi as that's where the relief should crack.. so cold throttle on thick oil shouldn't be over 48 or so...

    soundguy

  3. #3
    New Member
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    Oct 2012
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    3
    Location
    Jefferson City, MO.
    Tractor
    1947 8n Ford

    Default Re: 8n-High oil pressure

    Thanks for the info! I won't be back to the farm till this weekend. I will check the relief plunger. As far as hydraulic lock would the spark plugs have been wet with gas, anti freeze, or oil and/or came out the exhaust at start up? Just hoping that was it and not something more serious. When I pull the plunger out, are there obvious things to look for? Should I unhook an oil line and blow air backwards in the system for any obstructions?

  4. #4
    Epic Contributor Soundguy's Avatar
    Join Date
    Mar 2002
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    48,804
    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: 8n-High oil pressure

    at the time of hyd lock, there might have been something showing on the plugs.

    whatever was locking it likely drained thru the rings while setting.. thus there was nothing to blow out the exhaust.. not that it would have made it past the exhaust valves anyway unless open...

    i wouldn't blow air BACk thru the system...

    stuck plunger is what i would look for... it will have a flat spot onthe end.. that's normal..

  5. #5
    Veteran Member Jerry/MT's Avatar
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    Feb 2008
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    2,059
    Location
    Western Montana
    Tractor
    New Holland TD95D, Ford 4610 & Ferguson TO-30

    Default Re: 8n-High oil pressure

    Your relief valve is probably stuck closed.

    On newer or newly rebuilt engines, the relief valve is most likely opened somewhat and some of the oil is bypassed to hold the design oil pressure. As the engine wears, the valve moves toward closing, holding design pressure, until the wear gets great enough to cause the oil pressure to start to drop below the relief setting. As the engine continues to wear, about the only time the valve will open is with high viscosity oil (either cold oil or a hot, higher SAE viscosity grade oil). Eventually, with increased wear, the oil pressure will be higher when cold then drop lower as the oil heats up and the clearances open and the oil pressure will remain low. The relief valve will have no influence on the oil pressure at this point unless it sticks open

    On my TO-30 with a rebuilt engine , the pressure is independent of viscoity, oil temperature and engine rpm.It stays at 27 psig at all times that engine is running.

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