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Technical SBC Motor smoking mystery

Discussion in 'The Hokey Ass Message Board' started by Scumdog, Oct 12, 2019 at 6:54 PM.

  1. Scumdog
    Joined: Mar 3, 2010
    Posts: 605

    Scumdog
    Member

    Hi All, I know generally only God knows what's wrong with a motor before it's pulled down

    But here goes; got an '8Os' OT truck with sbc, possibly a 305.

    On start up cold it runs great, then after 45 seconds or so it starts smoking out of the right hand tail-pipe, a bit on the left side too but not that noticeable.

    As the motor warms up the smoke really pours out of the tailpipes, just about all out of the right hand one - which also 'puffs' a bit.

    Disconnecting the hose that runs from the passenger side valve cover to the air filter sees fumes/smoke puffing out of that hose.

    Going down a long hill sees no (visible) smoke behind the truck but going back up it looks like a crop-duster plane is going up the road, smoke everywhere!

    Points of note: the po has overfilled the oil - but not by much, maybe 3/8th inch, compressions all within 10lb but lower than the Haynes manual says they should be, motor runs great hot or cold.

    Any ideas before I tear it down - or fit another motor?
     
  2. BJR
    Joined: Mar 11, 2005
    Posts: 5,710

    BJR
    Member

    Bad oil rings is my guess.
     
  3. It sounds like it’s plain worn out


    Sent from my iPhone using H.A.M.B.
     
  4. 32v
    Joined: May 20, 2007
    Posts: 920

    32v
    Member
    from v.i.

    is it auto or standard
     
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  5. Scumdog
    Joined: Mar 3, 2010
    Posts: 605

    Scumdog
    Member

    My suspicion too, 57Fargo - possibly even damage to a piston on the passenger side as evidenced by the 'puffs' of smoke on a regular basis.
     
  6. Scumdog
    Joined: Mar 3, 2010
    Posts: 605

    Scumdog
    Member

    It's auto TH350
     
  7. How much lower ?
    You could do a leakdown test as well.
    And this sounds like a great candidate for a new crate engine.
     
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  8. Desoto291Hemi
    Joined: Apr 21, 2009
    Posts: 635

    Desoto291Hemi
    Member

    Overfilled oil will cause one to smoke like you described.
    Usually has to be way over,,,but try draining some of it out to take that from the equation.

    Tommy
     
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  9. 32v
    Joined: May 20, 2007
    Posts: 920

    32v
    Member
    from v.i.

    check 6 and 8 plug for fouling
    if they are check modulater valve
     
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  10. Deuces
    Joined: Nov 3, 2009
    Posts: 17,606

    Deuces
    Member
    from Michigan

    Valve seals need replaced?????.......
     
  11. blowby
    Joined: Dec 27, 2012
    Posts: 5,891

    blowby
    Member
    from Nicasio Ca

    Just drive it in 45 second bursts. :)

    If it's puffing out the breather hose, and the PCV valve is working, you got worn out rings.
     
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  12. sdluck
    Joined: Sep 19, 2006
    Posts: 2,178

    sdluck
    Member

    Older 305 and 350 had a problem sucking oil from the valley side of the intake manifold.replace intake gasket look for oil in the intake ports
     
  13. Rickybop
    Joined: May 23, 2008
    Posts: 5,654

    Rickybop
    Member
    from Michigan

  14. Rickybop
    Joined: May 23, 2008
    Posts: 5,654

    Rickybop
    Member
    from Michigan

  15. lippy
    Joined: Sep 27, 2006
    Posts: 3,983

    lippy
    Member
    from Ks

    I agree with Tommy, drain the oil down to the proper level, but sounds like bad rings to me. Your results may vary. Lippy
     
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  16. lippy
    Joined: Sep 27, 2006
    Posts: 3,983

    lippy
    Member
    from Ks

    Might as well do like sdluck says, your gonna have the intake off anyway. Lippy
     
  17. Pull valve covers and ensure drain-back holes aren't plugged. Easy check.
     
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  18. Scumdog
    Joined: Mar 3, 2010
    Posts: 605

    Scumdog
    Member

    Yep, that's the plan, I have heard of this issue with the intake gasket not sealing the bottom of the ports, even saw it on an episode of Fantom Works.
     
  19. blowby
    Joined: Dec 27, 2012
    Posts: 5,891

    blowby
    Member
    from Nicasio Ca

    If the intake gaskets were sucking in oil it would happen under high vacuum, like going downhill, like valve guides, I think.
     
  20. Budget36
    Joined: Nov 29, 2014
    Posts: 2,219

    Budget36
    Member

    Seems like blow by to me, but if you feel it runs fine, then weigh the cost of carrying some oil vs pulling the engine and having it rebuilt.
     
  21. Scumdog
    Joined: Mar 3, 2010
    Posts: 605

    Scumdog
    Member

    Ahem, when I said it smokes it SMOKES!!

    Backing into the workshop fills it so full of smoke that it looks like SWAT has paid a visit.
     
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  22. Baumi
    Joined: Jan 28, 2003
    Posts: 2,163

    Baumi
    ALLIANCE MEMBER

    Check if you´ve got a bad vacuum modulator on your th350. You might aswell be sucking ATF into the intake manifold. I had that happen and the engine smoked after warm up I couldn´t see anything in my rearview miror. Easy fix though.
     
  23. Evidence of trans modulator sucking oil would be a loss of trans fluid without noticeable puddles.
     
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  24. Desoto291Hemi
    Joined: Apr 21, 2009
    Posts: 635

    Desoto291Hemi
    Member

    Yes,,,,and transmission fluid smokes like a freight train!

    Tommy
     

  25. What can you easily get in New Zealand?

    Rebuild kits, pistons, and machine work or junk yard SBC, or new crate motors?

    That truck probably has the better of the 305 heads.
     
  26. What he said...
     
  27. And when it’s blowing smoke out of the breathers/valvecovers as well as the tail pipe with the cranking compression even across all 8 but “lower” than the printed manual specs,,,,
    That pretty much condemned the engine.

    If a leakdown test were performed my suspicions would be results relatively equal reading across all 8 cylinders but percentages too high.

    We’ve got no history provided. And ALL of the rings could be mysteriously stuck or it could be a good engine that worked hard and evenly till the end of its useful life and now needs a rebuild.

    As far as being over full,,, if it’s smoking that bad it would not be over full for too long and in need of more oil soon.

    Really no mystery here other than the actual reading from the compression test that’s lower than manual specs.
     
  28. LM14
    Joined: Dec 18, 2009
    Posts: 1,683

    LM14
    Member
    from Iowa

    How many miles are on it?
     
  29. X-cpe
    Joined: Mar 9, 2018
    Posts: 648

    X-cpe

    If it's the modulator, the smoke tends to be bluer than engine oil.
     
  30. ccain
    Joined: Jun 13, 2009
    Posts: 123

    ccain
    Member

    Seconded. Back when I didn't have two pennies to rub together, I bought a cheap 88 C1500 with a 305 as a daily. Smoked just like you described.

    My boss, at the machine shop I worked at at the time, suggested I pop the valve covers and make sure the oil drain-back holes weren't completely sludged up. Sure as shit, they were.

    I carefully dug all the crap out with a coat hanger, and also cleaned the rest of the crap that was laying in there. Must have gone through all the shop rags I had.

    Changed the oil, put it all back together and the smoking went away. Fix only cost the price of valve cover gaskets and an oil change. Ran the truck for 3 more years until it spun a bearing.

    It's worth a look.
     

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