Compression Test 140-120-35-120

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  • bjmorel
    #1

    Compression Test 140-120-35-120

    I have been trying to get my 1980 GS750L running for awhile, I did the Carb cleaning thing and it would only run on choke. I just did a compression test and I got 140-120-35-120. I know the answer is probably rings or valve seats, but was hoping someone here might have an idea that doesn't include a rebuild. I checked the valve lash on the bad cylinder and it had at least 0.004 in. when the cam lobe was opposite the valve plate. Any ideas?

    Brian
    Tags: None
    • Guest
      #2
      Pour a little oil in the 35 psi cylinder and see if the number rises. If it does it's probably rings. Did the bike sit for awhile?

        Comment

        • bjmorel
          #3
          The bike sat for some time before I bought it for $450, not sure how long though.

          Brian

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            • Guest
              #4
              Your rings might be froze up. You might be able to free them up with some penetrating oil.

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                • Jethro
                  Forum LongTimer
                  Charter Member
                  GSResource Superstar
                  Past Site Supporter
                  • May 2002
                  • 17888
                  • The only Henniker on earth
                  #5
                  Most people wouldn't, but I'd pour some Marvel Mystery Oil in there, turn it over by hand a few dozen times, let it sit overnight and then- stomp the ever loving sh!t out of it the next day.
                  Currently bikeless
                  '81 GS 1100EX - "Peace, by superior fire power."
                  '06 FZ1000 - "What we are dealing with here, is a COMPLETE lack of respect for the law."

                  I ride, therefore I am.... constantly buying new tires.

                  "Tell me what kind of an accident you are going to have, and I will tell you which helmet to wear." - Harry Hurt

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                    • chiphead
                      #6
                      Originally posted by Jethro
                      Most people wouldn't, but I'd pour some Marvel Mystery Oil in there, turn it over by hand a few dozen times, let it sit overnight and then- stomp the ever loving sh!t out of it the next day.
                      I like your style. What have you got to lose except a little metal[-o<

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                        • rkubik
                          #7
                          where buy MMO?

                          where do you buy this Marvel Mystery Oil? Sounds like something I could use. Napa, Walmart?

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                            • rpickle
                              #8
                              Both probably carry it. I have picked it up at AutoZone.

                              Rick

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                                • vtcycle
                                  #9
                                  The MM oil is a good suggestion, sometimes.

                                  My 1971 Honda SL175 has MM oil in it for the past 2 weeks, and is still froze up. Looks like a total tear down is in order.

                                  Oh well, it will give my son something to do and hopefully keep him out of trouble for a few weeks.:-D

                                  peace,
                                  michel

                                    Comment

                                    • BadBillyB
                                      #10
                                      Originally posted by bjmorel
                                      I have been trying to get my 1980 GS750L running for awhile, I did the Carb cleaning thing and it would only run on choke. I just did a compression test and I got 140-120-35-120. I know the answer is probably rings or valve seats, but was hoping someone here might have an idea that doesn't include a rebuild. I checked the valve lash on the bad cylinder and it had at least 0.004 in. when the cam lobe was opposite the valve plate. Any ideas?

                                      Brian
                                      Dont know if your bike has the vacuum hose for the petcock going to #3 carb. If it does and the diaphragm is ruptured in the petcock, cyl #3 may be washed down with fuel. Block off the fuel going to the carbs, drain the float bowl for #3, do the overnight MM oil soak and see if your compression comes back up....If not, do a leak down test.......BadBillyB

                                        Comment

                                        • Guest
                                          #11
                                          On the 80 it connects to the #2 carb. Which carb is it if you go 1-4 left to right sitting on the bike?

                                            Comment

                                            • bjmorel
                                              #12
                                              Number 3. The Vacuum is on number 2, but it is plugged right now.

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