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Cylinder Head Problems - cracked??

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by BigBadJap, Jun 19, 2003.

  1. BigBadJap

    BigBadJap Registered Member

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    Hi. Since I bought my 89 Jimmy, it has used oil. I knew that when I bought it, but I didn't think it would go through as much as it does.

    Here are the symptoms:
    208 000KM - 125 000Mi all stock
    About 3 seconds to start engine from cold
    Instantly starts when warm and puffs blue smoke on startup
    Compression is ~135-140 on all cylinders EXCEPT #8 is 120
    #8 Sparkplug black and tarry
    Coolant is clean
    Vacuum Gauge reads ~18" but rapidly quivers between 17 and 18"
    Runs great when cold, no blue smoke at all - no pinging.
    Different story when at operating temperature...
    Cruising very light throttle for a while, then slightly increase throttle produces a two or three very quick knocks and a big blue puff out of the exhaust.
    Pedal to the metal when hot, blue smoke trailing vehicle.

    I think the engine is actually quite strong. I've got 3.42 open diff on stock tires and can chirp the tires from dead stop.

    I initially thought the problem was all in the valve guides and seals as indicated by the vacuum gauge, BUT from what I have read, worn guides and seals should not affect engine compression. I understand that oil being sucked into the engine can cause detonation from increased compression, and as the oil becomes less viscous at running temperature more oil can be sucked in...

    But does anybody think that there is more wrong here than just worn valve guides/seals?
     
  2. BRN78BLAZER

    BRN78BLAZER 1/2 ton status

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    doesn't sound like your heads are cracked. Valve guides could leak, but more likely it sounds like the rings are worn if the compressions down a bit and blue smoke trails on hard accel. But if it runs good other than that, I would suggest you dumped somw heavy weight oil in it. 20w50 is what my uncle used to run in his oil burner, and it helped quite a bit. Also put a few squirts of oil into the cylinder then do the compression test. If it reads higher it is worn rings, the oil will seal them for a few cranks.
    I think the engine is actually quite strong. I've got 3.42 open diff on stock tires and can chirp the tires from dead stop.

    Then if you can, just replace the rings and hone the cylinders. That is if your not looking to rebuild or buy a new engine.

    Good Luck -Steve-
    After all this if it rings, and as you say [ QUOTE ]


    [/ QUOTE ]
     
  3. BRN78BLAZER

    BRN78BLAZER 1/2 ton status

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    ok my post screwd up... hmmm, maybe thats why that preveiw selection is there, o well sorry.

    Here is what I was trying to quote

    [ QUOTE ]
    I think the engine is actually quite strong. I've got 3.42 open diff on stock tires and can chirp the tires from dead stop.



    [/ QUOTE ]

    The I was suggesting that if you aren't looking to spend money on a rebuild or a new engine, and want to keep using thick oil then you could just hone out the cylinders and put a set of rings in it. The sell rings specifically for oil burning engines.

    anyway good luck -steve-
     
  4. BigBadJap

    BigBadJap Registered Member

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    Hmm.. I'm just not convinced it's rings. Why would only one cylinder be 120 while every other cylinder is around 140.
     
  5. BRN78BLAZER

    BRN78BLAZER 1/2 ton status

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    Hmmm, mot sure, but I know my 305 has 150-170 all around. Find out what the compression is for your motor, and if there is and overall drop of atleast say 20psi, then you can assume there is something wrong compression wise. Also try the wet test. If the pressure increases you know your rings are worn. a wet test will not increase compression if the rings are good.
     
  6. imiceman44

    imiceman44 1 ton status

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    [ QUOTE ]
    Hmm.. I'm just not convinced it's rings. Why would only one cylinder be 120 while every other cylinder is around 140.

    [/ QUOTE ]

    Actually when only one is low, it usually is the valves, the rings tend to wear almost evenly.
     
  7. BigBadJap

    BigBadJap Registered Member

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    What would the impact on the rest of the engine be if I were to get some remanufactured heads and slap them on without a bottom end rebuild? (Assuming that the rings are in decent condition)
     
  8. blasterD

    blasterD 1/2 ton status

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    Assuming that your rings are good, a new/rebuilt set of heads should cure your problem. Try the wet compression test first though, just to rule out rings.
     
  9. BigBadJap

    BigBadJap Registered Member

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    Ya... Actually, I think I'll get a leak down test done on the engine. That should confirm things for me.

    I always hear: "You can't replace the top end without the bottom end going..."

    What exactly does that mean? Even if the bottom end does go, is there potential to cause damage to the new top end?
     
  10. Panther

    Panther 1/2 ton status

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    I haven't heard that per se, but I assume it means that once you tighten up the top, the rings will go faster.

    The valve seals that were keeping your cylinder pressure down at 120 are now sealed up. Because the presssure was low, there wasn't too much stress on your rings. Now the rings will be your weak point and will wear faster.
     
  11. imiceman44

    imiceman44 1 ton status

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    [ QUOTE ]
    I haven't heard that per se, but I assume it means that once you tighten up the top, the rings will go faster.

    The valve seals that were keeping your cylinder pressure down at 120 are now sealed up. Because the presssure was low, there wasn't too much stress on your rings. Now the rings will be your weak point and will wear faster.

    [/ QUOTE ]

    Exactly.
    /forums/images/graemlins/thumb.gif
     
  12. BigBadJap

    BigBadJap Registered Member

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    That I can live with. If I can delay the inevitable for even a year, I'll be a happy camper.

    I unfortunately have more ambition than money.
     

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