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  • #1

    Compression

    bike has been really hard to start but once going works fine and lots of power.. sometimes she use to hesitate so i figured it was carbs dirty. i also added half liter of oil for 710km's so i was thinking that maybe rings bad so to ease my mind i check the compression and #3 was lower..
    #1- 135
    #2- 135
    #3- 120
    #4- 135
    is it possible that my valve lash could be causing this little amount of difference although that dont explain the oil, i still aiming towards rings on #3. what are the next steps to look for before stripping her down?
    1980 Yamaha XS1100LG Midnight Special
    Tags: None
  • #2
    Not unusual for one to be off and the basic rule is 10%, which you are just a touch over. I would adjust valves first and try that again.

    Also, try adding a teaspoon or tow of oil to the cylinder and let it soak for about ten minutes, then try the compression test again. If the number improves noticably then you have some level of confirmation it is the rings.
    Life is what happens while your planning everything else!

    When your work speaks for itself, don't interrupt.

    81 XS1100 Special - Humpty Dumpty
    80 XS1100 Special - Project Resurrection


    Previously owned
    93 GSX600F
    80 XS1100 Special - Ruby
    81 XS1100 Special
    81 CB750 C
    80 CB750 C
    78 XS750

    Comment

    • #3
      Originally posted by captjanes View Post
      bike has been really hard to start but once going works fine and lots of power.. sometimes she use to hesitate so i figured it was carbs dirty. i also added half liter of oil for 710km's so i was thinking that maybe rings bad so to ease my mind i check the compression and #3 was lower..
      #1- 135
      #2- 135
      #3- 120
      #4- 135
      is it possible that my valve lash could be causing this little amount of difference although that dont explain the oil, i still aiming towards rings on #3. what are the next steps to look for before stripping her down?
      You might want to reconsider taking it apart, stock size rings are VERY difficult to obtain if not impossible. It would be cheaper and easier to start with checking the valve clearances...
      '79 XS11 F
      Stock except K&N

      '79 XS11 SF
      Stock, no title.

      '84 Chevy K-10 "Big Blue"
      GM 350, Muncie SM465, NP208, GM 10 Bolt with 3.42gears turnin 31x10.5 Baja Claws

      "What they do have is an implacable, unrelenting presence and movement that bespeaks massive power lurking behind paint and chrome. They don't wail like a screeching ninja, the don't rumble like a harley. They just growl like a spactic, stressed out badger waiting to rip your face off and eat your soul." Trainzz~RIP~

      Comment

      • #4
        compression check: engine warm, plugs out, tci unplugged, ive put around 5k miles on it this year, the only thing i forgot to do was open the throttle, 149/150/155/155.....
        also the valves were recently done...
        just to give u an idea...
        79 XS11 special "Loki" - homemade 4-2 exhaust, pod filters, rebuilt forks with progressive springs, tkat fork brace, progressive shocks, rebuilt all brakes and MC's, rebuilt carbs with #142.5 main and #42.5 pilot, a custom front and chin fairing, and a handmade set of saddlebags....

        09 YZF-R1 " Toothless"

        04 Buell XB12R "Butterfly"

        "I had a name at some point, a birth-name, but now everyone just calls me Wolf...."

        Wolf
        Moto Militia MC

        Comment

        • #5
          Originally posted by airborneXS View Post
          compression check: engine warm, plugs out, tci unplugged, ive put around 5k miles on it this year, the only thing i forgot to do was open the throttle, 149/150/155/155.....
          also the valves were recently done...
          just to give u an idea...
          Those are pretty good numbers considering your throttle wasn't full open.

          I did mine last year and got 155, 140, 150, 160. And my valve clearances were all too tight then. (and still are )
          (that 160 on #4 was after I replace the piston because the previous one had a hole in it)
          Last edited by GLoweVA; 07-26-2012, 12:46 PM.
          Hi, my name is George & I'm a twisty addict!

          80G (Green paint(PO idea))
          The Green Monster
          K&N A/F, TC's fuse block, '81 oil cooler, TC's homemade 4-2 w/Mac Mufflers, Raptor 660 ACCT
          Got him in '04.
          bald tire & borrowing parts

          80SG (Black w/red emblems & calipers)
          Scarlet
          K&N A/F, TC's fuse block, WJ5, Shoei bags, Raptor 660 ACCT.
          Got her in '11
          Ready for the twisties!

          81H (previously CPMaynard's)
          Hugo
          Full Venturer, Indigo Blue with B/W painted tank.
          Cold weather ride

          Comment

          • #6
            Just pulled plugs I got 150,150,130,150 I put oil on #3 and got 150,150,180,150 so I guess rings are gone on #3.. She started before now I can't even get her to start.. My spark also looks very weak I can barley see it.. Should I change pistons as well or just the rings on that piston?
            1980 Yamaha XS1100LG Midnight Special

            Comment

            • #7
              Don't just assume you've got to replace those rings just yet.

              I bet if you put a little oil in all the other cylinders, those numbers would go up too.

              If you can't get it to start, I'd look at the spark issue first.
              The compression numbers 130 going to 180 sure indicates that the rings on #3 MIGHT need some TLC, but they also may just 'free' up and start sealing better again after running some.
              Get the bike running again first, then warmed up and try the compression readings again. Even with 130# on #3 you should be able to get it running.
              re-reading your first post, you probably need to clean your carbs, paying attention to the pilot/idle circuits. Get those clean and adjusted right and she should start right up on choke and then once warmed up idle okay.

              Occasionally you can find stock sized rings on ebay. (I got mine last year from there) (you may be able to re-use the rings in there. They may just be 'misaligned'. They've got to be so many degrees offset from each other, otherwise there's a path for the compression to 'leak' by into the case.
              Hi, my name is George & I'm a twisty addict!

              80G (Green paint(PO idea))
              The Green Monster
              K&N A/F, TC's fuse block, '81 oil cooler, TC's homemade 4-2 w/Mac Mufflers, Raptor 660 ACCT
              Got him in '04.
              bald tire & borrowing parts

              80SG (Black w/red emblems & calipers)
              Scarlet
              K&N A/F, TC's fuse block, WJ5, Shoei bags, Raptor 660 ACCT.
              Got her in '11
              Ready for the twisties!

              81H (previously CPMaynard's)
              Hugo
              Full Venturer, Indigo Blue with B/W painted tank.
              Cold weather ride

              Comment

              • #8
                If a bike has been setting there will always be a little build up of rust on one cylinder or the other because the valves on one are always open. You may find that after continued running the rings will reseat and the value will improve some. You may want to run it for a couple of hundred miles and see if it improves.
                To fix the problem one should not make more assumptions than the minimum needed.

                Rodan
                https://www.youtube.com/watch?v=khm6...liHntN91DHjHiS
                1980 G Silverbird
                Original Yamaha Fairfing and Bags
                1198 Overbore kit
                Grizzly 660 ACCT
                Barnett Clutch Springs
                R1 Clutch Fiber Plates
                122.5 Main Jets
                ACCT Mod
                Mac 4-2 Flare Tips
                Antivibe Bar ends
                Rear trunk add-on
                http://s1184.photobucket.com/albums/z329/viperron1/

                Comment

                • #9
                  DO NOT pull it apart! Those compression numbers are better than lots start with. Get it running as is and run it for awhile (1000 miles or so maybe) and then if you feel like it check compression again. Over time the rings freeze up and stuck. Running it for awhile and getting some heat cycles is the best thing to help that and get the rings to repeat.

                  I REPEAT DO NOT TEAR THE ENGINE APART! NUMBERS ARE GOOD!!!!!
                  Nathan
                  KD9ARL

                  μολὼν λαβέ

                  1978 XS1100E
                  K&N Filter
                  #45 pilot Jet, #137.5 Main Jet
                  OEM Exhaust
                  ATK Fork Brace
                  LED Dash lights
                  Ammeter, Oil Pressure, Oil Temp, and Volt Meters
                  Green Monster Coils
                  SS Brake Lines
                  Vision 550 Auto Tensioner

                  In any moment of decision the best thing you can do is the right thing, the next best thing is the wrong thing, and the worst thing you can do is nothing.

                  Theodore Roosevelt

                  Comment

                  • #10
                    My compression is about 100 PSI across the board. It does not start at the tap of the button, but it starts, and runs pretty well really. So I think you are focusing way to hard on that one cylinders compression number.

                    If you know you have a spark issue, focus on that before you go tearing into the engine.
                    Life is what happens while your planning everything else!

                    When your work speaks for itself, don't interrupt.

                    81 XS1100 Special - Humpty Dumpty
                    80 XS1100 Special - Project Resurrection


                    Previously owned
                    93 GSX600F
                    80 XS1100 Special - Ruby
                    81 XS1100 Special
                    81 CB750 C
                    80 CB750 C
                    78 XS750

                    Comment

                    • #11
                      If you use the "choke", don't give it any throttle or it defeats the function of the choke. (But you probably knew that). I have one 78E model that I have to turn the petcocks to prime if the bike has been sitting a week or more, AND also use the choke once the carbs are filled.
                      Skids (Sid Hansen)

                      Down to one 1978 E. Stock air box with K&N filter, 81H pipes and carbs, 8500 feet elevation.

                      Comment

                      • #12
                        Hi CaptJanes,
                        as others have already said get her running and put some miles on her or kilometers in your case Mine used lots of oil for the first 1000km after a long time in a barn. 25000km later hardly uses a drop of oil.
                        I would not open the motor
                        Phil
                        1981 XS1100 H Venturer ( Addie)
                        1983 XJ 650 Maxim
                        2004 Kawasaki Concours. ( Black Bear)

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