Compression Check on removed motor

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  • crazy steve
    XS-XJ Guru MODERATOR
    • Jan 2009
    • 7932
    • Beautiful outer Yelm, WA

    #16
    I'll repeat... check the valve clearances. Too-tight valves can drop compression numbers by 2/3. The XS valves get tighter (not looser) as they wear and this is a common problem on neglected motors.
    Fast, Cheap, Reliable... Pick any two

    '78E original owner - resto project
    '78E ???? owner - Modder project FJ forks, 4-piston calipers F/R, 160/80-16 rear tire
    '82 XJ rebuild project
    '80SG restified, red SOLD
    '79F parts...
    '81H more parts...

    Other current bikes:
    '93 XL1200 Anniversary Sportster 85RWHP
    '86 XL883/1200 Chopper
    '82 XL1000 w/1450cc Buell, Baker 6-speed, in-progress project
    Cage: '13 Mustang GT/CS with a few 'custom' touches
    Yep, can't leave nuthin' alone...

    Comment

    • skids
      XS-XJ Super Guru
      • Jul 2002
      • 5048
      • Florissant, CO, USA

      #17
      Originally posted by crazy steve
      I'll repeat... check the valve clearances. Too-tight valves can drop compression numbers by 2/3. The XS valves get tighter (not looser) as they wear and this is a common problem on neglected motors.
      And by that, you are talking about shim-to-lobe measurement getting tighter right? As that measurement gets tighter the actual valve gets looser (opens bigger).
      Skids (Sid Hansen)

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

      Comment

      • crazy steve
        XS-XJ Guru MODERATOR
        • Jan 2009
        • 7932
        • Beautiful outer Yelm, WA

        #18
        Yes. I've personally seen tight valves reduce compression numbers by as much as 100 lbs, lesser reductions are very common. Once valve clearances get below about .003", the valve 'closed' duration gets shorter. So before you go off on a tangent with leakdown tests and pulling the head, this should be the first thing you look at if you get low numbers...
        Fast, Cheap, Reliable... Pick any two

        '78E original owner - resto project
        '78E ???? owner - Modder project FJ forks, 4-piston calipers F/R, 160/80-16 rear tire
        '82 XJ rebuild project
        '80SG restified, red SOLD
        '79F parts...
        '81H more parts...

        Other current bikes:
        '93 XL1200 Anniversary Sportster 85RWHP
        '86 XL883/1200 Chopper
        '82 XL1000 w/1450cc Buell, Baker 6-speed, in-progress project
        Cage: '13 Mustang GT/CS with a few 'custom' touches
        Yep, can't leave nuthin' alone...

        Comment

        • copeland3300
          XSive
          • Apr 2012
          • 50
          • Ft George G Meade, Maryland

          #19
          OK, so I checked the other bike and I got similar numbers.

          I'll check the valve clearances and see what I can figure out.

          How do I do that again?
          1980 XS1100G - Coming together
          1979 XS1100 Midnight Special - Still in one rusted piece

          Comment

          • copeland3300
            XSive
            • Apr 2012
            • 50
            • Ft George G Meade, Maryland

            #20
            Ah, I found the section in the service manual on how to do this.

            Where can I get the shims without getting dealer gouged?
            1980 XS1100G - Coming together
            1979 XS1100 Midnight Special - Still in one rusted piece

            Comment

            • bikerphil
              Master of XSology
              • Jan 2008
              • 8640
              • South Flori-DUH

              #21
              New 29MM valve shims...

              Valve Shims for Bikes in CRC2's Online Catalog of New motorcycle Parts and Accessories Indy
              2H7 (79) owned since '89
              3H3 owned since '06

              "If it ain't broke, modify it"

              โ˜ฎ

              Comment

              • Rasputin
                XS-XJ Super Guru
                • Apr 2008
                • 3180
                • Lacombe, Alberta, Canada

                #22
                There is also supposed to be a valve shim library on this site, but as I have heard nothing about it lately I do not know who runs it or if it even exists now. Many members like myself will swap shims if we have what you need. Often it is just a matter of posting the values you need and see who has them.
                2-79 XS1100 SF
                2-78 XS1100 E Best bike Ever
                80 XS 1100 SG Big bore kit but not fully running yet.
                Couple of more parts bikes of which 2 more will live!

                Comment

                • copeland3300
                  XSive
                  • Apr 2012
                  • 50
                  • Ft George G Meade, Maryland

                  #23
                  Hmmm, ok. I googled around and found these and other resources. I was hoping there'd be some secret stash somewhere, haha.

                  I'll post again when I know more about my clearances.
                  1980 XS1100G - Coming together
                  1979 XS1100 Midnight Special - Still in one rusted piece

                  Comment

                  • Rasputin
                    XS-XJ Super Guru
                    • Apr 2008
                    • 3180
                    • Lacombe, Alberta, Canada

                    #24
                    I know I have at least 20 shims lying around here. Problem is some are the same size value so it ends up being 10 different shim sizes I have available for swap. Once you know what you need post it up and others will help if they can.
                    2-79 XS1100 SF
                    2-78 XS1100 E Best bike Ever
                    80 XS 1100 SG Big bore kit but not fully running yet.
                    Couple of more parts bikes of which 2 more will live!

                    Comment

                    • copeland3300
                      XSive
                      • Apr 2012
                      • 50
                      • Ft George G Meade, Maryland

                      #25
                      I figured out what I have and what I need. I don't have the paper on me, but I figured it out using the manual. Crazy Steve was right, things got tighter!

                      Anyway, I also came across this if anyone is interested:



                      They're more expensive than the other place, but it's another resource.
                      1980 XS1100G - Coming together
                      1979 XS1100 Midnight Special - Still in one rusted piece

                      Comment

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