Number 5 cylinder smoking

Discussion in 'Troubleshooting & Diagnosis' started by sped, Dec 26, 2017.

  1. sped

    sped New Member

    19
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    Sep 28, 2014
    Henderson, NV
    I have a '72 Chevelle with a 350 crate motor, millage is less then 5000 miles on it but it keeps fouling out #5 cylinder spark plug. When I am on the freeway doing 70MPH I hit the throttle and some blue smoke appears but when I let off lots of smoke appears.
    I just did a compression test and it was a solid 125 as were the rest of the bank on that side. A friend said I have varnish built up in the oil rings from letting the car sit too long. Could it be that? I also thought it may be a bad valve seal.

    Any suggestions?

    Regards,
    Ed
     
  2. CorkyE

    CorkyE Veteran Member Lifetime Gold Member

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    Ringgold, GA
    Sounds more like a bad valve guide and/or seal, try replacing the seal first since it's the easiest. The reason it smokes when you let off the gas, the engine has high vacuum and it's sucking oil past the seal.
     
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  3. bourbon_scotch

    bourbon_scotch Veteran Member Lifetime Gold Member

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    maybe its just a bad spark plug
     
  4. CorkyE

    CorkyE Veteran Member Lifetime Gold Member

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    Ringgold, GA
    I've never seen a bad spark plug cause an engine to smoke, but there are a lot of things I haven't seen. A bad plug can cause fouling, but not smoke.
     
  5. Rdobbs1977

    Rdobbs1977 Huge Guns N Roses Fan

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    Dec 1, 2014
    Nashville
    i'm with corkye so far. bet if you put a vacuum gauge on there, you'll see a flick in the needle. if it is a loose valve guide or worn seal, a leak down tester if you have one is not going to validate that. never hear of the varnish/ring thing, sounds like a stretch there. i've fired up motors that sat for years with no smoke issues.
     
  6. bourbon_scotch

    bourbon_scotch Veteran Member Lifetime Gold Member

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    what color is the second smoke?
     
  7. Blown Camaro

    Blown Camaro Veteran Member

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    Dec 13, 2009
    Deltona, FL
    Valve guides. Pull the heads and send them out.
     
  8. cadillac_al

    cadillac_al Veteran Member

    540
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    Apr 22, 2015
    Maine
    It could be a bad intake gasket seal on that cylinder sucking oil from the valley. Did you install the intake with good gaskets or was it already installed?
     
  9. Mike N

    Mike N Moderator Staff Member Lifetime Gold Member

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    Spencerport, NY.
    125 seems low to me. Did you have all the plugs out of the engine and the throttle propped wide open for that compression test?
     
  10. sped

    sped New Member

    19
    1
    Sep 28, 2014
    Henderson, NV
    I pulled the intake and found the gasket had moved on installation, could be sucking oil from the valley. I also changed the valve seals on #5. I am waiting for new gaskets and will put it back together as soon as I get them, we'll see what happens.

    Thanks for all the replies!

    Ed
     
    FlaJunkie likes this.

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