cold compression on new engine

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  • p_s
    #1

    cold compression on new engine

    New head gasket and rings, honed bores, lapped old valves that passed the gas test.
    Cold compression is 110 psi on #1, 75 on the rest.
    Bad?

    I had poured unequal amounts of oil into the bores when I was doing rings, which would explain the difference. The question is if 75 is bad and I need to redo the head gasket.
    Tags: None
    • GavinJuice
      #2
      You got the throttle WIDE OPEN? Has the engine even been run yet? if not...fast idle till warm up then RIP ITTTTTTTTTT!

        Comment

        • p_s
          #3
          No carbs, no exhaust, no electrical parts, never been started.

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            • Nessism
              Forum LongTimer
              GSResource Superstar
              Past Site Supporter
              Super Site Supporter
              • Mar 2006
              • 35788
              • Torrance, CA
              #4
              Compression test at this point is pretty meaningless. As long as the bores were within spec, and you honed the cylinders and installed new rings, you shouldn't have anything to worry about.
              Ed

              To measure is to know.

              Mikuni O-ring Kits For Sale...https://www.thegsresources.com/_foru...ts#post1703182

              Top Newbie Mistakes thread...http://www.thegsresources.com/_forum...d.php?t=171846

              Carb rebuild tutorial...https://gsarchive.bwringer.com/mtsac...d_Tutorial.pdf

              KZ750E Rebuild Thread...http://www.thegsresources.com/_forum...0-Resurrection

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                • Thomas Kenny
                  #5
                  You might want to consider a "Leak-down" test on it since you can't get it to operating temperature??? A leak-down test will tell you if your rings and valves are sealing properly.

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                    • Guest
                      #6
                      Slap that baby together and seat the rings before taking a compression test. Run it at first startup at about 3000 rpm for twenty minutes or so.
                      Then ride it for 500 miles. Retourque head and then worry about compression. There should be no worry if the cylinders were done right and the ring gap is correct.

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                        • SqDancerLynn1
                          #7
                          You could have one of the cams 1 tooth off ???? On my 45 K mile original 850 with stone cold engine I get 120-130 psi

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                            • p_s
                              #8
                              I added a bit of oil to #4 and then got 150 psi before I stopped. I guess the numbers are just meaningless with a new, cold engine. (I also adjusted all the valves on the bench first.)

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                                • SqDancerLynn1
                                  #9
                                  The motor could be a little tight since it hasn't been run, could be turning slow

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                                    • p_s
                                      #10
                                      Originally posted by SqDancerLynn1
                                      The motor could be a little tight since it hasn't been run, could be turning slow
                                      It's turning very slowly actually. The battery could do with a charge as well. I'd like to hear the engine run, but I still have to swap the front and rear suspension, mount new tires, sprockets, chain, all the controls, ... I'm enjoying it though. I'm glad I picked up an air compressor and an impact wrench before I started the project.

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