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  • Wierd compression results

    So i was changing the timing belt today, and decided to go ahead and change the plugs while i was working. While i had the old plugs out i did a compression test. Came up with 3 210's, 1 205, 1 195, and 1 odd cylinder was 145. It runs perfect, but it smokes and if you hold your hand in front of the exhaust a light film of oil will cover your hand. I was thinking it was a valve stem seal before the test, just because it ran so good. But now i am debating if it is a head gasket or the rings. Hoping some restore or lucas will help out. I want to n2o this thing, but now i am not so sure. Oh yea and this is the 85 NA. Any suggestions would be appreciated.
    KILL HADJI

  • #2
    do a leak down test. when you test each cylinder make sure its at tdc with on the comp stroke and pressurize that cylinder. listen in the radiator for head gasket leak, listen in the intake for intake valve leak, exhaust for exhaust valve and oil cap for rings. repeat with all cylinders
    85 Z31 6.0 LSX turbo 766whp/792wtq
    04 GTO, LS6, big cam, porting, N20... underway for summertime daily driver.

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    • #3
      What if i don't have an air compressor readily available. Also it isn't burning any coolant, it is oil. So if i got my hands on some compressed air, would i feel for air on the breather opening? Also with that how would i be able to tell the difference between the air going through the oil passages on the gaskets or through the rings?
      KILL HADJI

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      • #4
        Hmm. well you can poor a cap full of oil into the spark plugs hole crank the engine a couple of times to let the oil get all around the rings (acts as a seal) then do your comp test again. if your numbers go up from what they were then its your rings that are fuxored. otherwise it could be the head gasket, intake valve or exhaust valve.
        85 Z31 6.0 LSX turbo 766whp/792wtq
        04 GTO, LS6, big cam, porting, N20... underway for summertime daily driver.

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        • #5
          210 is high anyway

          non-turbo should be around 165, turbo slightly less 145-ish, unless you have brand new rings or something then maybe more

          anything above 120 is ok as far as an engine goes as long as you don't have too much variation (fsm lists 14psi difference max)

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          • #6
            Ahh, nice little trick. I will try that tomorrow, hopefully a little addittive will help. Any suggestions on an oil addittive? I have heard lucas and restore were the top two, but i have never really tried either. thanks!

            210 is high anyway
            I was thinking the same thing. You should have seen the look on my face, my bro thought something was wrong and about shit himself. The previous owner did some work to the heads, i think. I was thinking that somebody shaved the head or resurfaced it too much and it upped the CR. Maybe that would explain the amazingly high results.
            KILL HADJI

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            • #7
              an additive for what you are trying to do should be a temparary solution, unless you dont care about the car. whatever your comp pressure is, a variation as high as that is very very not good. we did a comp test in a turbo civic with JE pistons and it had 145 highest and 110 lowest and we pulled it apart and found chunks of piston missing in two cylinders! Not small chunks either.

              Your situation could be either really really bad as far as the pistons go or it could just be that you are running on half of a ring. no way to tell unless you do the leak down or pull it apart. :?
              85 Z31 6.0 LSX turbo 766whp/792wtq
              04 GTO, LS6, big cam, porting, N20... underway for summertime daily driver.

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              • #8
                Did the smoke and oily exhaust start before or after the t-belt ?

                Just thinking that the recent maintenance could have possibly made the issue or made it worse. Just a thought.
                Just stand back and throw money.
                Performance costs money.
                Reliable performance costs more.

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