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low compression has me stumped.

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  • low compression has me stumped.

    Well I finally got my car runnning decent and it had a small consistent misfire. So I bought some new plugs and while I was changing them I did a compression test. 150, 148,130,148. video VV

    http://www.facebook.com/photo.php?v=275262599202873

    So I figured it has to be a blown head gasket, or a bent valve or something, I was not thinking and just didn't even do a wet test. But there was no scoring on cylinder 3 wall , I took all the valves out and none are bent, and I dont see any signs of a blown head gasket.





    The cylinders look to be in great condition. I can still see all the crosshatching and no signs of wear.

    I am going to take the head to have a valve job done with some new valve stem seals, BC springs and a valve job. Any direction would be greatly appreciated.
    2008 crew cab z71 DD
    1998 240sx se
    2012 Chevy Equinox family hauler

  • #2
    You are already going in the right direction.

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    • #3
      How long had the engine been run? That small of a variance could be a stuck ring, so you could do some seafoam and run it hard and they'll usually free up.

      My old engine had about a 8-10 psi spread between a couple of cylinders, but some seafoam and a few track events and they were all dead on 155.
      '18 Chevrolet Volt - Electric fun hatch for DD duty!


      DefSport Koni Sleeve and Spring Perch Buy!!!
      http://www.nissanroadracing.com/showthread.php?t=5902

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      • #4
        yeah... freshen the head and put it back together and drive the piss out of it.
        Originally posted by SoSideways
        I don't care what color they are as long as they are LONG AND HARD.
        '04 G35 Sedan 6MT- The DD
        '96 240SX- The Track Toy

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        • #5
          Yea, even if a valve isn't bent you can have a small nick or angle mismatch on a valve to have a small leak. Being that much down it's probably not more than 1 valve.
          '18 Chevrolet Volt - Electric fun hatch for DD duty!


          DefSport Koni Sleeve and Spring Perch Buy!!!
          http://www.nissanroadracing.com/showthread.php?t=5902

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          • #6
            I had put aero kroil in the cylinders and I had driven the piss out of it several times. The miss was only after it had warmed up. Also both the intake and exhaust cam were off 1 tooth, both clickwise . I am just going to do a little more investigating. I just don't want to miss anything.
            2008 crew cab z71 DD
            1998 240sx se
            2012 Chevy Equinox family hauler

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            • #7
              Misfire only at operating temperature is going to be in the cylinder head. Looks like you have a carbon trail at #3 cylinder. Sticking valves will cause this, too.

              I agree. Check the cylinder head and correct valve timing.

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              • #8
                Ok thanks for all the help. I dropped the head off at the machine shop today and they are going to do a valve job, and I asked them to do a pressure check and a thorough inspection of everything. He is going to get into it tonorrow I will let you guys know what's up when I get it back.
                2008 crew cab z71 DD
                1998 240sx se
                2012 Chevy Equinox family hauler

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                • #9
                  So I went up to the machine shop today, and they said that all of my exhaust valve guides were sloppy. Then he told me he already ordered them. I then explained to him that if they aren't coming from a performance shop or Japan they probably aren't right. Well he said he measured the ID, OD and length and found some that are .001 longer. He said they would be fine. Should I just order some Jwt or oem guides and tell him to hold off or just let him move forward? The ones he got were cast iron. I am just worried about quality and dependability.
                  2008 crew cab z71 DD
                  1998 240sx se
                  2012 Chevy Equinox family hauler

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                  • #10
                    cast Iron Valve Guides?

                    not on a turbo car, you need soething like bronze or BeCu to dissipate the heat into the head, I wouldn't allow him to assemble with cast iron
                    I am SKULLWORKS

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                    • #11
                      Originally posted by Tower240sx View Post
                      cast Iron Valve Guides?

                      not on a turbo car, you need soething like bronze or BeCu to dissipate the heat into the head, I wouldn't allow him to assemble with cast iron
                      What this ahole said...
                      '18 Chevrolet Volt - Electric fun hatch for DD duty!


                      DefSport Koni Sleeve and Spring Perch Buy!!!
                      http://www.nissanroadracing.com/showthread.php?t=5902

                      Comment


                      • #12
                        So, the machinist claims valve guide excessive clearance for #3 low compression and other cylinders?

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