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'81 GS650G: Aftermarket oversize pistons hit head

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    #16
    Just maybe the 750 bigbore bit for the 650 will fit into a 550 with 650 Barrels and 550 head. the shape of the 550 pistons more resemble the 740 kitt.........

    550 pistons are the only GS pistons to have a raised crown the 740 BBK could fit
    1-264.jpg
    82 GS650E (Canadian), 83 XS650SK (Canadian), Main machines Running
    Aussie, 74 TX650A, 80 XS650SG, 81XS650SH, 80XS850, in various states of repair/disrepair
    Introduction and ongoing thread for myGS650Ez
    Albums

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      #17
      Just checked the x-ref for cylinders, head and pistons between the G and the E models.
      The exact same parts.
      Looks like Cruzin ballsed it up, there's no way of fitting them.
      ---- Dave
      79 GS850N - Might be a trike soon.
      80 GS850T Single HIF38 S.U. SH775, Tow bar, Pantera II. Gnarly workhorse & daily driver.
      79 XS650SE - Pragmatic Ratter - goes better than a manky old twin should.
      92 XJ900F - Fairly Stock, for now.

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

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        #18
        That's all really unfortunate, I'm very sorry to hear all of this. The Honda CB 750 big bore kits that they sell, maybe even other CB models, are very popular and get great reviews for the long-term & short-term. Engine builders and machine shops have told owners that the pistons seem to be the same quality as OEM.
        They just went out on a limb on the GS650 kit, and really did not look into the cylinder head design whatsoever. I doubt they had a head in hand or even a mold of a combustion chamber when they "designed" those. I'm willing to bet that they are identical to their GS750 8v 77-79 stock piston offering, which also will not work on a 650 head, and probably not on a stock GS550 head either...

        In the past I had considered helping out my friend who could not afford one of the Wiseco 740 kits, to perhaps fit a GS650 cylinder bored for stock GS750 8V pistons, with a 1980 - 1982-ish 8V GS550 head.

        65mm is really the limit for the 650 cylinders in regards to the stud spacing and sleeve location. And also, the 550 combustion chambers are a slight bit smaller than the 750 combustion chambers, and the valve spacing is slightly closer together as far as the valve relief locations in the pistons.
        I deemed it potentially a possibility to do some machine work to the pistons to cut down the outer perimeter of the crown slightly, and cut new valve reliefs inboard slightly further towards the center of the piston, and make that work. Or possibly machine the combustion chamber slightly larger as well as cutting the valve reliefs different in the pistons.
        Last edited by Chuck78; 05-25-2021, 08:28 PM.
        '77 GS750 920cc heavily modded
        '97 Kawasaki KDX220R rugged terrain ripper!
        '99 Kawasaki KDX220R​ rebuild in progress
        '79 GS425stock
        PROJECTS:
        '77 Suzuki PE250 woods racer
        '77 GS550 740cc major mods
        '77 GS400 489cc racer build
        '76 Rickman CR1000 GS1000/1100
        '78 GS1000C/1100

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          #19
          Originally posted by 650Skull View Post
          From the cruzinimage site description for the GS650 - 740 BBK. Cruzinimage state the pistons are a different shape

          81-83 SUZUKI GS650 740cc BIGBORE PISTONS KIT 65mm PISTON


          -DESCRIPTION-◆10-GS650BB◆
          *81-83 Suzuki GS650 Bigbore pistons kit with Head Gasket
          Aftermarket
          Piston size: 65mm( 3.00mm Oversize )
          Head gasket: Bore size is 68mm
          *Set includes: pistons, pins, clips,rings and head gasket
          Note: Cylinder boring required
          These pistons are aftermarket.different design from of the Suzuki genuine pistons
          I bought these pistons back in 2019. Can't recall if the text back then also mentioned it has a different piston design.
          What I know is, that it already had the 'note' part that the cylinder needs boring.

          If they call it the 'GS650 bigbore kit' and mention a different design, I would expect them to also mention, that these pistons won't ever work in the original GS650 head. Anyway, that's my 2 cents. Learned my lesson and paid for it.

          This is just information for other people that also look into this option.
          Vancouver, BC
          Suzuki GS 650G '81

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            #20
            Originally posted by Berti View Post
            I bought these pistons back in 2019. Can't recall if the text back then also mentioned it has a different piston design.
            What I know is, that it already had the 'note' part that the cylinder needs boring.

            If they call it the 'GS650 bigbore kit' and mention a different design, I would expect them to also mention, that these pistons won't ever work in the original GS650 head. Anyway, that's my 2 cents. Learned my lesson and paid for it.

            This is just information for other people that also look into this option.
            Didn't mean for my post to sound aggressive. Tried to alter the font size but it wouldn't do it.

            These 650/740 BBK piston being th wrong shape has been mentioned on other threads.

            Cruzinimage XS650 pistons, standard size up to the BB 700cc pistons are spot on and no one has had any trouble with them.

            Tiss unfortunate. here is a thread with a couple of links to the 740 pistons, and some information on a bulk buy situation from wisco

            82 GS650E (Canadian), 83 XS650SK (Canadian), Main machines Running
            Aussie, 74 TX650A, 80 XS650SG, 81XS650SH, 80XS850, in various states of repair/disrepair
            Introduction and ongoing thread for myGS650Ez
            Albums

            Comment


              #21
              Those pistons def look like the gs750 2 valve pistons. Back in my day i took my 550 and punched it out to a 650 like everyone does. But then I took the 750 pistons and bored out the cylinder and installed a cylinder spacer to drop the pistons in the bore in order for them to clear the valves. It worked but the combination of everything didn't really provide the power delivery i was hoping for. Plus the motor ran HOT.

              I would recommend NOT using those pistons.
              1980 Gs550e....Not stock...

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                #22
                Hey everyone,

                Just wanted to let you guys know - with great help from Chuck I was able to "finish" the engine. He was very kind to send me over a set of the Wiseco pistons and after some more machining on my side I was finally able to put the engine together this weekend. Have to take photos and show them to you guys.

                But I'm a very happy guy now. I can 'easily/freely' rotate the crankshaft and everything looks/feels smooth. Time to get the rest going on this never ending project.... I originally wanted to ride this summer. But looks more like I will be done on time for christmas haha
                Vancouver, BC
                Suzuki GS 650G '81

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                  #23
                  Yay, Chuck.
                  If you're not living on the edge, you're taking up too much space.

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