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GS 650G crankshaft and signal generator

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    GS 650G crankshaft and signal generator

    Hi guys, this is my first post after browsing the site with much admiration for the knowledge here I'm asking for a bit of help.
    I'm busy building a 650 katana out of a bunch of old parts and junk. Time consuming but so far very rewarding.
    So far I am still at the stripping / cleaning / measuring and cataloging stage, and things are going pretty well except for 2 problems. I have been chatting a few people here in South Africa about these, and there seems to be a variety of opinions. So I thought I'd ask for your opinions too and try to build up a consensus!
    Problem No 1: (the main one) - Crankshaft. All 6 main journals seem to be fine, 3 of the crank pins are hovering just under the limit, while the 4th is way undersized and oval (0.3mm in one axis and 0.8 in the other). Obviously oil starved at some point. (And probably why I picked the engine up cheap!) My options so far seem to be:
    Option 1) Weld the bad crank pin, straighten, and grind all 4 crank pins down to the first U/S bearing shells (0.25mm U/S). Assuming I can source the shells, the shop will match the crank pins to the bearings.
    Option 2) Hard chrome all crank pins and re-grind back to stock.
    Option 3) Find another crankshaft. (Unlikely to happen).
    As you can imagine, I want to make the right decision here.
    Problem No 2: Signal generator plate. I don't have one. I do, however, have a GS 550M signal plate. Would that work in my bike if the correct wiring connections are done? (it seems from the circuit diagrams that one end of the 650 pulse generator coils are connected together and earthed, while the 550's are routed to the igniter). Surely they are just coils with a magnet? or do they have different windings? etc etc.
    One last point, here in South Africa it is difficult and expensive to order parts from overseas due to unreliable and expensive postage plus HORRENDOUS exchange rate. If I have to buy parts then I will, but I would rather not!
    Oh yes, if I am really stuck, then I could possibly build up the parts as a GS 550 with 650 top end. The 550 gear box and crankshaft which I have seem to be good, but I really wanted the shaft drive. Also the nearly new seat I found is for a 650, about an inch and a half longer than the 550 seat... Like I said, it's all good fun!
    Thanks guys, hope to hear from you.
    Ian

    #2
    Not suggesting you buy this, but it might be worth investigating-

    sigpicSome of the totally committed probably should be.
    '58 + '63 Vespa 150's' (London, GB/RI, US)
    '67 X6 T20 ('67 Long Beach, Ca.- misty-eyed)
    '71 Kaw. A1-ugh ('71 SF, CA- worked @ Kaw dlr)
    '66 Yam. YL1('72 SF-commuter beater)
    '73 Kaw. S2A-2Xugh ('73 SF-still parts slave)
    '78 GS 750C ('77 SF-old faithful-killed by son)
    '81 KZ 750E ('81 SF-back to Kaw. dlr)
    '81 GS 650G ('08 back to NE&ME- (project)
    '82 GS '82 (2) GS650GZ, L, Middlebury, G current

    Comment


      #3
      Thanks, good spot.
      I've sent a query re postage. Let's see

      Comment


        #4
        Hi Ian

        Welcome to this site from a fellow GS enthusiast in SA!

        The GS650G Katana is a really nice bike, and is scarce here in SA. My brother has one that has only done about 15,000 km. If you can build it up to look original, it will really be worth your efforts.

        Send me a photo of the right hand side of your engine where the signal generator plate goes, and I will enquire at a local bike breaker.
        1981 GS850G "Blue Magic" (Bike Of The Month April 2009)

        1981 GS1000G "Leo" (Bike Of The Month August 2023)

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          #5
          Hi "2BRacing:"

          I'm afraid I can't send you a picture as the engine is completely stripped, but it should be pretty much identical to your 850. I believe the signal generators are the same. As I mentioned, the 550 plate seems to fit, but the wiring is different. Although the circuit diagram doesn't show the current path through the "black box" of the igniter so I'm not sure exactly where the common wire goes on the 550. As for breaker yards, Bike Hospital found me a signal generator but they wanted R1500 for it. As I'd seen the same thing advertised on e-bay from a breakers yard in the Netherlands for 35 euros you can imagine I wasn't impressed. (40 euros shipping from Netherlands though, and that's without considering our postal workers strike!)
          Just out of interest, my previous bike was a (1979?) GS 1000 E which I bought with 1000 km on the clock, and sold about 5 years later and retired from biking. But now I've earned my mid-life crisis, and can still remember drooling when the first katanas came out. Hence this project!
          ps, "recycled 64", the shipping on that crankshaft was $184 (R 2125). Not an option I'm afraid, but thanks anyway.

          Comment


            #6
            Hi Ian

            A local bike breaker in Cape Town has the signal generator for a GS650G, but he wants R1 425 for it. Seems like these breaker guys are also into "price fixing", as that is similar to Bike Hospital's price!
            1981 GS850G "Blue Magic" (Bike Of The Month April 2009)

            1981 GS1000G "Leo" (Bike Of The Month August 2023)

            Comment


              #7
              Originally posted by 2BRacing View Post
              Hi Ian

              A local bike breaker in Cape Town has the signal generator for a GS650G, but he wants R1 425 for it. Seems like these breaker guys are also into "price fixing", as that is similar to Bike Hospital's price!
              Yep, seller's market it seems.

              I'm sure that gs 550 signal generator plate will work...

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