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How critical is lobe position when checking valve clearances?

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    How critical is lobe position when checking valve clearances?

    Resurrecting an '81 GS550T with 8k miles. Don't know if the valves have been checked so I opened it up. Most of the valve clearances are within the spec ranging from .04mm to .07mm, but a few only hit the spec as the cam shaft turns thru it's rotation. Some of them are a little tight in other positions during the rotation, albeit not when the lobe would be engaging the shim.

    So ... how critical is it that the lobes are the the official position per http://gsarchive.bwringer.com/bikecl...lve_adjust.pdf and only that position when checking clearance? I've always assumed that the lobes were a constant radius during the portions that do not contact the shim.The clearances are so close that swapping in a different shim may throw them out of spec. unfortunately they are currently close on the tight side, rather than the safer loose side.
    Last edited by sacruickshank; 12-04-2020, 09:21 PM.
    Current rides: GS650L, GS550T, GL500, GL1100, Bonnie, Triumph Adventurer, Guzzi California

    #2
    I too was wondering about the off side of the cam.

    but what do need to concider about cam position when checking clearance is to have the 2 cams that are next to each other , both off the bucket at the same time. If one is depressing it’s spring, it is also pushing the cam shaft around and is effecting the clearance reading of the other cam.
    http://webpages.charter.net/ddvrnr/GS850_1100_Emblems.jpg
    Had 850G for 14 years. Now have GK since 2005.
    GK at IndyMotoGP Suzuki Display... ... GK on GSResources Page ... ... Euro Trash Ego Machine .. ..3 mo'cykls.... update 2 mocykl


    https://imgur.com/YTMtgq4

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      #3
      So, yes, cam lobe positions is important.

      so the answer to if should be pointed up, or pointed forward or pointed back is : one forward and the one next to it backward, so neither on that side (say, exhaust 1 & 2) is pushing againnst spring.
      http://webpages.charter.net/ddvrnr/GS850_1100_Emblems.jpg
      Had 850G for 14 years. Now have GK since 2005.
      GK at IndyMotoGP Suzuki Display... ... GK on GSResources Page ... ... Euro Trash Ego Machine .. ..3 mo'cykls.... update 2 mocykl


      https://imgur.com/YTMtgq4

      Comment


        #4
        When using the factory cam positioning the valves are checked in PAIRS, with the adjacent valve to the one you are checking on the base circle. This is important because if you check the clearance with the lobe pointed away from the bucket the adjacent valve may be depressed, and when that's happening it skews the cam in the journal clearance which increases the measured clearance.

        I've done comparisons both ways and when the adjacent valve is depressed it results in a measured clearance about .002" (.05mm) more than with the factory positioning. That's not much, but considering how tight the factory spec is, it's significant.

        Bottom line, if you want to adjust the valves with the lobe pointing away from the bucket you should target a higher clearance range: at .07mm at a minimum. And speaking of clearance, you should always target the top end of the clearance range and consider increasing the clearance up to .12mm. Kawasaki KZ bikes use clearances up to .15mm and the GS 8V engine is a KZ clone so what's good for the goose is good for the gander. There is no reason to target the tighter Suzuki clearance unless you are willing to keep on top of your measurements checks per the manual. If you are prone to skipping checks, target the higher range.
        Last edited by Nessism; 12-05-2020, 01:36 PM.
        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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          #5
          Thanks @Redman and @Nessism for the info. That makes sense.

          I'll check them again once I get the engine back to life. I suspect some residue from sitting may be affecting the clearances. Plus I'll need to change the petrified gasket and I'm not yet ready to tackle that bit of torture. The valve cover came off with minimal damage to the gasket, so it's re-usable for short test starts but not long-term riding.
          Current rides: GS650L, GS550T, GL500, GL1100, Bonnie, Triumph Adventurer, Guzzi California

          Comment


            #6
            Just checked mine on a 1980550e
            This gets it spot on ! from proper workshop manual.
            and yes you when in right position do 2 at once.

            p.s let's have a pic of the bike .... I like to see
            these old bikes.

            20201205_165249.jpg
            UKJULES
            ---------------------------------
            Owner of following bikes:
            1980 Suzuki GS550ET
            1977 Yamaha RD 250D
            1982 Kawasaki GPZ 750 R1
            1980 Suzuki GSX 250E

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              #7
              this may help to get started .....

              20201205_165404_resize_0.jpg
              UKJULES
              ---------------------------------
              Owner of following bikes:
              1980 Suzuki GS550ET
              1977 Yamaha RD 250D
              1982 Kawasaki GPZ 750 R1
              1980 Suzuki GSX 250E

              Comment


                #8
                Originally posted by ukjules View Post
                Just checked mine on a 1980550e
                p.s let's have a pic of the bike .... I like to see
                these old bikes.
                I have problems uploading photos directly, so here's an imgur link. Not a beauty queen but relatively low miles, looks to never have been dropped, and no one has chopped anything off. Some PO did go a little crazy with spray paint.

                And the "need it gone" price was right.

                Discover the magic of the internet at Imgur, a community powered entertainment destination. Lift your spirits with funny jokes, trending memes, entertaining gifs, inspiring stories, viral videos, and so much more from users.
                Current rides: GS650L, GS550T, GL500, GL1100, Bonnie, Triumph Adventurer, Guzzi California

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                  #9


                  1978 GS 1000 (since new)
                  1979 GS 1000 (The Fridge, superbike replica project)
                  1978 GS 1000 (parts)
                  1981 GS 850 (anyone want a project?)
                  1981 GPZ 550 (backroad screamer)
                  1970 450 Mk IIID (THUMP!)
                  2007 DRz 400S
                  1999 ATK 490ES
                  1994 DR 350SES

                  Comment


                    #10
                    sacruickshank
                    Since you already an Imgur account, it’s just a few extra steps to post pics so they show up in the thread instead of just the link. Follow the link in my signature about using Imgur, post #6 in that thread.

                    Rich
                    1982 GS 750TZ
                    2015 Triumph Tiger 1200

                    BikeCliff's / Charging System Sorted / Posting Pics
                    Destroy-Rebuild 750T/ Destroy-Rebuild part deux

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                      #11
                      Thanks Rich, i'll use that next time.

                      For the record, the bike does have the fenders and throttle, they just weren't mounted at the time of the photo. It does not have a headlight (will buy), functional seat or side panels, so those will be make or buy decisions.
                      Current rides: GS650L, GS550T, GL500, GL1100, Bonnie, Triumph Adventurer, Guzzi California

                      Comment


                        #12
                        Originally posted by Nessism View Post
                        Bottom line, if you want to adjust the valves with the lobe pointing away from the bucket you should target a higher clearance range: at .07mm at a minimum.
                        I have a slight problem with that suggestion, Ed.

                        You had mentioned that the cam could be skewed in the journal by the adjacent lobe pushing on a valve. That is very correct, but it only happens for one of the two valves in that pair. If you set the clearance loose for both of them, one might end up just right, but the other one will be too loose.

                        Loose isn't all that bad, within reason, but it also helps of the clearances are somewhat consistent.

                        .
                        sigpic
                        mine: 2000 Honda GoldWing GL1500SE and 1980 GS850G'K' "Junior"
                        hers: 1982 GS850GL - "Angel" and 1969 Suzuki T250 Scrambler
                        #1 son: 1986 Yamaha Venture Royale 1300 and 1982 GS650GL "Rat Bagger"
                        #2 son: 1980 GS1000G
                        Family Portrait
                        Siblings and Spouses
                        Mom's first ride
                        Want a copy of my valve adjust spreadsheet for your 2-valve per cylinder engine? Send me an e-mail request (not a PM)
                        (Click on my username in the upper-left corner for e-mail info.)

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                          #13
                          Steve,
                          When adjusting the valves with the lobe pointing away you can't adjust the valves in pairs. The crank/cams must be repositioned for each valve you are checking. I haven't checked every position but pretty sure that for each valve, then the lobe is pointed away from the bucket, the adjacent valve will be depressed, thus it's important to target a higher clearance range.
                          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


                            #14
                            Very true, you can NOT adjust in pairs if you do it the wrong way,which is what many of the new guys think is correct. And that is because that's the way that most cars get adjusted.

                            It's definitely best to follow the factory procedure to position two adjacent lobes so they are pointing about 45° away from their respective valves and adjust them as a pair.

                            All three service manuals (Factory, Clymer, Haynes) show that same goofy picture that says "position the cams like this", but only the factory manual puts into text that you position the cams for a PAIR of valves and check them BOTH without moving the cam.

                            Once it is understood exactly how to position the cams and WHY, it makes the procedure go so much easier and quicker.

                            .
                            sigpic
                            mine: 2000 Honda GoldWing GL1500SE and 1980 GS850G'K' "Junior"
                            hers: 1982 GS850GL - "Angel" and 1969 Suzuki T250 Scrambler
                            #1 son: 1986 Yamaha Venture Royale 1300 and 1982 GS650GL "Rat Bagger"
                            #2 son: 1980 GS1000G
                            Family Portrait
                            Siblings and Spouses
                            Mom's first ride
                            Want a copy of my valve adjust spreadsheet for your 2-valve per cylinder engine? Send me an e-mail request (not a PM)
                            (Click on my username in the upper-left corner for e-mail info.)

                            Comment


                              #15
                              Originally posted by Steve View Post
                              Once it is understood exactly how to position the cams and WHY, it makes the procedure go so much easier and quicker.

                              .
                              This ^^^^^^^^^^. For years I adjusted them by appearance, one at a time (heel of cam at bucket) and by adopting the proper method it made things a bit easier and quicker.
                              ---- Dave

                              Only a dog knows why a motorcyclist sticks his head out of a car window

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