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Half Moons MUST Be Replaced???

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    #1

    Half Moons MUST Be Replaced???

    Hey guys ~ planning on doing my first valve check & adjust.
    Wondering if the half moons must be replaced if they still look like they are in good shape. I have the tappet tool, gasket, and feeler gauge on the way....

    Didn't realize the half moons MIGHT need replaced as well.
    I will be checking every 4,000 miles on my '82 GS750TZ.

    Is this something required each time you pull the valve cover?!?!
    Thanks in advance!
    Tags: None
    #2
    It really depends on how well they come out in the first place - sometimes I've replaced them and a couple of times I was lucky and didn't need to.
    Cowboy Up or Quit. - Run Free Lou and Rest in Peace

    1981 GS550T - My First
    1981 GS550L - My Eldest Daughter's - Now Sold
    2007 GSF1250SA Bandit - My touring bike

    Sit tall in the saddle Hold your head up high
    Keep your eyes fixed where the trail meets the sky and live like you ain't afraid to die
    and don't be scared, just enjoy your ride - Chris Ledoux, "The Ride"

    Comment

      #3
      Originally posted by cowboyup3371 View Post
      It really depends on how well they come out in the first place - sometimes I've replaced them and a couple of times I was lucky and didn't need to.
      In the pictures I'm seeing on a valve check, the half moons don't look like they are even removed during the process.
      What would you recommend as far as checking them?
      Pull them out and inspect/replace?
      If so, do they need to be sealed back down with something?
      Leave them be?

      Appreciate the input as I'm new to the process.
      It seems easy enough, just want to do it right.

      Comment

        #4
        You typically don't need to replace them unless they have shrunk or cracked. Use some Ultra Black silicone or Three Bond sealer on the curved area of the seal and bond it in place. As long as the flat section is flush or sits a little proud of the gasket surface, you should be fine. If they are stuck in the engine and not leaking, leave them alone.
        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

        Comment

          #5
          Originally posted by Nessism View Post
          You typically don't need to replace them unless they have shrunk or cracked. Use some Ultra Black silicone or Three Bond sealer on the curved area of the seal and bond it in place. As long as the flat section is flush or sits a little proud of the gasket surface, you should be fine. If they are stuck in the engine and not leaking, leave them alone.
          Very informative. Thank you sir!

          Comment

            #6
            What Nessim said... but you could tell that couldn't you? If they're out I would just see if they're still pliable or not. If they're hard they might have shrunk some, best to replace them as they're cheap.
            "Men will never be free until Mark learns to do The Twist."

            -Denis D'shaker

            79 GS750N

            Comment

              #7
              What Ed says. One of mine stuck to the gasket when I removed it once and the other times I could see they were visibly torn.
              Cowboy Up or Quit. - Run Free Lou and Rest in Peace

              1981 GS550T - My First
              1981 GS550L - My Eldest Daughter's - Now Sold
              2007 GSF1250SA Bandit - My touring bike

              Sit tall in the saddle Hold your head up high
              Keep your eyes fixed where the trail meets the sky and live like you ain't afraid to die
              and don't be scared, just enjoy your ride - Chris Ledoux, "The Ride"

              Comment

                #8
                I love the Ultra Black for such uses. Like was said, a little smear on the curved surface of the head AND ( for me anyway ) the half moons. I let it set up about 10 minutes or so to get more sticky than slimey and then set the half moons in place. Use a straight edge to get them setting pretty level across the flats in relation to the heads gasket surface.

                A little proud is good in that when the cover seats it will squish the RTV nice and leak proof.
                MY BIKES..1977 GS 750 B, 1978 GS 1000 C (X2)
                1978 GS 1000 E, 1979 GS 1000 S, 1973 Yamaha TX 750, 1977 Kawasaki KZ 650B1, 1975 Honda GL1000 Goldwing, 1983 CB 650SC Nighthawk, 1972 Honda CB 350K4, 74 Honda CB550

                NEVER SNEAK UP ON A SLEEPING DOG..NOT EVEN YOUR OWN.


                I would rather trust my bike to a "QUACK" that KNOWS how to fix it rather than a book worm that THINKS HE KNOWS how to fix it.

                Comment

                  #9
                  Its a misnomer that the half moos " shrink". They are metal plugs that are rubber coated. What happens is the metal gets squished so many times and they get loose. Yes they can be picked up with a magnet..i discovered this myself when one stuck to my pencil magnet on the bench.
                  Last edited by chuck hahn; 10-20-2013, 10:00 AM.
                  MY BIKES..1977 GS 750 B, 1978 GS 1000 C (X2)
                  1978 GS 1000 E, 1979 GS 1000 S, 1973 Yamaha TX 750, 1977 Kawasaki KZ 650B1, 1975 Honda GL1000 Goldwing, 1983 CB 650SC Nighthawk, 1972 Honda CB 350K4, 74 Honda CB550

                  NEVER SNEAK UP ON A SLEEPING DOG..NOT EVEN YOUR OWN.


                  I would rather trust my bike to a "QUACK" that KNOWS how to fix it rather than a book worm that THINKS HE KNOWS how to fix it.

                  Comment

                    #10
                    Originally posted by chuck hahn View Post
                    Its a misnomer that the half moos " shrink". They are metal plugs that are rubber coated. What his the metal gets squished so many times and they get loose. Yes they can be picked up with a magnet..i discovered this myself when one stuck to my pencil magnet on the bench.
                    Ha! Did not know that! Of course rubber still shrinks, gets hard, and cracks whether it's wrapped around metal or not. I guess the metal limits the distortion of dimensions that come with age.
                    "Men will never be free until Mark learns to do The Twist."

                    -Denis D'shaker

                    79 GS750N

                    Comment

                      #11
                      true that Allie. But my surmation is that even though the rubber coating looks fine and undamaged, its more the metal base is squished and we all know that its not gonna be spinging back. Its squished and thats that in the end run. Yes the new gaskets thickness does press them down again, but maybe a bit less than if they were new. Thats why i like the Ultra Black as a stop gap for them.
                      MY BIKES..1977 GS 750 B, 1978 GS 1000 C (X2)
                      1978 GS 1000 E, 1979 GS 1000 S, 1973 Yamaha TX 750, 1977 Kawasaki KZ 650B1, 1975 Honda GL1000 Goldwing, 1983 CB 650SC Nighthawk, 1972 Honda CB 350K4, 74 Honda CB550

                      NEVER SNEAK UP ON A SLEEPING DOG..NOT EVEN YOUR OWN.


                      I would rather trust my bike to a "QUACK" that KNOWS how to fix it rather than a book worm that THINKS HE KNOWS how to fix it.

                      Comment

                        #12
                        A mechanic I know always replaces them because they are cheap and a failure means he has to redo the work for free. For home use, he told me to reuse them if the rubber is still pliable and not chewed up. Add a bit of black goo like Chuck suggests and they should be OK.

                        Jim
                        1981 GS550T (Long gone)
                        1983 GS650G (Rolling rebuild is now a full rebuild.)

                        Comment

                          #13
                          Thanks for the replies everybody.
                          I did the valve check/adjustment today.

                          Old gasket was destroyed (glad I had a new one).
                          However, the half moons were in great shape.
                          Utilized some gasket sealant, and it was good to go!!!

                          Comment

                            #14
                            I have used the cheap Vesra copies from Z1 Enterprises. They seem to work ok
                            sigpic Too old, too many bikes, too many cars, too many things

                            Comment

                              #15
                              Originally posted by 850 Combat View Post
                              I have used the cheap Vesra copies from Z1 Enterprises. They seem to work ok
                              Gasket & tappet set came from Z1. Worked like a charm!
                              Now just waiting on my oil filter & speedo cable.

                              Comment

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