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Burning Oil

Discussion in 'Early CJ5 and CJ6 Tech' started by garage gnome, May 10, 2019.

  1. May 10, 2019
    garage gnome

    garage gnome ECJ5 welder

    Western MA
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    The rebuilt F head in my '56 smokes like crazy only after I let off the throttle from going up a hill or pulling the plow. I have no idea where to start with this one. I'm thinking I should pull the plugs and see if the oil is getting by the pistons first.
     
  2. May 10, 2019
    rejeep

    rejeep Well-Known Member 2024 Sponsor 2023 Sponsor 2022 Sponsor

    Rochester, NY
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    PCV baffle?

    disconnect the PCV and see if it happens.. might be sucking oil under WOT
     
  3. May 10, 2019
    Glenn

    Glenn Kinda grumpy old man Staff Member

    Apopka, Fl
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    I assume you're smelling it too and not just seeing a condensation cloud? I would definitely check the plugs before anything else. Can you drive a bunch of miles and not see any smoke? Only happens when it's working hard? Positive it's not getting too much gas at a heavy throttle? Can you see oil use by checking the oil level?
     
  4. May 10, 2019
    PeteL

    PeteL If it wasn't for physics, and law enforcement... 2024 Sponsor 2023 Sponsor 2022 Sponsor

    Hills of NH
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    Compression test and vacuum test would be quick and cheap to see if one cylinder is bad.

    But usually bad oil-smoke is the reverse... worse upon hitting the gas after coasting down a hill. Are you sure it's not a fuel-rich condition? (Is the smoke blue, or black? Are the plugs oily/cruddy, or sooty?)
     
  5. May 10, 2019
    tarry99

    tarry99 Member

    Northern California
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    Valve guides or bad valve seals if it had any
     
  6. May 10, 2019
    PeteL

    PeteL If it wasn't for physics, and law enforcement... 2024 Sponsor 2023 Sponsor 2022 Sponsor

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    Aren't they likely to act up more in a high vacuum situation, rather than after heavy loading?
     
  7. May 10, 2019
    Glenn

    Glenn Kinda grumpy old man Staff Member

    Apopka, Fl
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    I know bad valve seals will certainly show on startup, especially after sitting.
     
  8. May 10, 2019
    Glenn

    Glenn Kinda grumpy old man Staff Member

    Apopka, Fl
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    Problems after a rebuild always make for head scratching. :)
     
  9. May 10, 2019
    tarry99

    tarry99 Member

    Northern California
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    He said: " only after I let off the throttle"........where vacuum would be present.................might be coming down the valve stem from the overhead into the combustion chamber and out the exhaust valve? ..............................Only a guess?
     
  10. May 10, 2019
    Glenn

    Glenn Kinda grumpy old man Staff Member

    Apopka, Fl
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    At least he only has 4 to check/wonder about.
     
  11. May 10, 2019
    garage gnome

    garage gnome ECJ5 welder

    Western MA
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    It doesn't smoke when it starts.
     
  12. May 10, 2019
    Glenn

    Glenn Kinda grumpy old man Staff Member

    Apopka, Fl
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    How many miles are on the rebuild? Does it have highway miles? Or should I say road miles?
     
  13. May 10, 2019
    garage gnome

    garage gnome ECJ5 welder

    Western MA
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    I don’t know how many miles it has. Daryl drove it around quite a bit after he rebuilt the engine. I’ve only driven it around the yard.
     
  14. May 10, 2019
    Chilly

    Chilly Active Member

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    Smokes after being under load, or under load as in dropped a gear and running high revs? Possibly pumping rocker box full of oil, then sucking it past the valve seals when you let off and vacuum goes high? Anything blocking drains from top of head back to crankcase?

    But since this is freshly rebuilt it seems odd to have valve seal leaks. Rich condition seems more likely. I dont know what carb you have or how it works but if it was a motorcraft 2100 I'd be thinking of a power valve that comes on later (lower vacuum), if in fact it is rich mixture and not oil.
     
  15. May 10, 2019
    62CheepJeep

    62CheepJeep Member

    Spartanburg SC
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    Mine smokes like a chimney upon goosing the throttle and under a load. I have no idea what is the issue with mine. I am afraid of going down the rabbit hole so to speak. Mine is a whitish blue smoke.

    Mine smoked using both stock Fuel/Vacuum pump and aftermarket pump without Vac for wipers.
     
    Last edited: May 10, 2019
  16. May 10, 2019
    1967 CJ5A

    1967 CJ5A Mike 2024 Sponsor 2023 Sponsor 2022 Sponsor

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    Do you have the combination fuel/vacuum pump? If there is a crack in the vacuum diaphragm, oil can be sucked through the diaphragm and into your pcv system. This happened to me and it took me a while to figure out how oil was being burned!
     
    PeteL and Glenn like this.
  17. May 10, 2019
    Glenn

    Glenn Kinda grumpy old man Staff Member

    Apopka, Fl
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    Interesting. Not something normally suspected. Usually fuel pump problems are gas in the oil.
     
  18. May 10, 2019
    garage gnome

    garage gnome ECJ5 welder

    Western MA
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    I rebuilt the vac/fuel pump. I can disconnect the vacuum pump and see if the problem goes away.
     
  19. May 10, 2019
    Jw60

    Jw60 Sitting up n buckled down. 2024 Sponsor 2023 Sponsor 2022 Sponsor

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    With my f-head I had the issue where the exhaust back pressure and intake pressure was entering the crankcase thru worn valve guides that have no seal and pushing everything out the breather which would go into the oil bath. It got 1 mile per quart of oil so that was rather extreme and unlikely under normal circumstances.
    But this was under load and wide open throttle.
    Edit:
    I would suspect an issue with the intake guides allowing oil to be drawn into the intake, or a pcv issue (it is positive crankcase ventilation)
     
    Last edited: May 11, 2019
  20. May 11, 2019
    Jw60

    Jw60 Sitting up n buckled down. 2024 Sponsor 2023 Sponsor 2022 Sponsor

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    Does your oil dipstick still have the baffle?
     
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