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Tracking down a knock on a '78 GS400. Need help getting the cylinder off.

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    Tracking down a knock on a '78 GS400. Need help getting the cylinder off.

    Ok so I recently finished rebuilding a 1978 GS400 I bought as a pile of parts for 100 bucks. If you're interested in seeing my journey and banging your head against the keyboard in rage, I'll be posting the album soon!
    Everything seemed to be going well and I managed to put a couple hundred miles on it with only a few hiccups, most of which were my fault.

    But I noticed as I started paying attention more that there was a definite noise coming from the engine. At first it seemed like it was coming from the top end so I did all the regular checks. Tappet shim clearances were within spec, cams looked good, no obvious problems there. Once I got the bike back running after I changed the valve cover gasket I decided to give everything a close listen with the old "screwdriver in the ear" trick and started poking around. When I put the screwdriver against the crankcase, right about where the clutch is, the noise was incredibly loud. Not quite a hollow knock, more of a tapping with some scraping or grinding. I checked all the clutch adjustments, everything was right, and the noise didn't really change regardless of the position of the clutch or whether or not it was in gear. It does seem to get quieter when revving but that might just be the sound of the engine overpowering whatever is making the noise. I have a couple videos of the sound but unfortunately they're mostly focused on the top end of the engine because this was when I was still convinced that was the location of the issue.

    So because I'm incredibly paranoid and the thought of blowing up this engine scares me to death, and because I'm not afraid of a rebuild for the experience, I decided to pull it in for the season and start tearing it down until I find a problem. So far everything has come apart with very little fuss aside from some stripped JIS screws, but I'll be replacing all the case screws anyway. But I finally hit a roadblock, and it's the cylinder itself. The head came off fine, and I've removed every bolt I can find, but no matter what I do the cylinder won't budge. I've tapped it from every angle, I've heated the gasket up, I've even put a couple bolts in the holes on top and tried a slide hammer. Nothing.

    There has to be something holding this cylinder on. The only thing I have found is a nut inside the camchain tunnel, but the problem is the nut is not exposed enough to get a socket on and there's no way you're getting a wrench in there. I also am not sure it needs to be removed and don't want to risk dropping it in the crankcase if it doesn't even need to come out.

    Has anyone had this problem? Please tell me I'm just a moron and I'm missing something obvious. I don't mind being stupid if it means an easy solution.

    Side note: Those two holes on the ends of the cylinders are threaded like bolts are supposed to go there, and the manuals mentions 6mm bolts in this location that are supposed to go through the head, but my head does not have holes through the top. There are bushings and shallow holes in the head that mate to these holes but the head does not have holes all the way through. I assume this was something added to the later models, but I thought I'd mention it in case it matters.


    Videos of sound:





    Picture of nut:



    Picture of current status:

    $100 1978 GS400 Rebuild (Outdated thread, new one soon!).
    - Indicator light diode mod
    - LED underglow kit
    - Aftermarket LED headlight bucket
    - Hex head engine case bolt kit
    - SH775A Reg/Rec upgrade
    - Dynatek Dyna S ignition
    - All Balls taper bearing steering stem mod
    - Dynatek 5ohm ignition coils and NGK caps
    - Custom cafe seat

    #2
    Sounds like the 43 year old base gasket has petrified and is (effectively) gluing the cylinder on tight.

    I'm not specifically familiar with the 400 but look for a good place to place a block of wood under the lowest row of fins so you can pry upward and break the cylinder off. DO NOT try to slip anything like a putty knife between the case and cylinder to get it loose, because that can mar the surfaces.
    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


      #3
      I tried putting a big trigger spreader under the front lip of the cylinder with one end on the ground. I managed to lift the front of the bike but made no progress on the gasket.
      I just can't believe I'm having this much problem, every other gasket has been no problem. They all crumble when you try to remove them but none of them have acted like an epoxy so far.

      Its seriously like someone JB Welded the cylinder on.
      $100 1978 GS400 Rebuild (Outdated thread, new one soon!).
      - Indicator light diode mod
      - LED underglow kit
      - Aftermarket LED headlight bucket
      - Hex head engine case bolt kit
      - SH775A Reg/Rec upgrade
      - Dynatek Dyna S ignition
      - All Balls taper bearing steering stem mod
      - Dynatek 5ohm ignition coils and NGK caps
      - Custom cafe seat

      Comment


        #4
        Yup, common problem.

        I use a piece of 2x4 and a mini sledge. You have to make sure to spread the impact load across a large area of the block or you will bust the fins.
        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
          So there's no chance that basically inaccessible nut is the problem?
          $100 1978 GS400 Rebuild (Outdated thread, new one soon!).
          - Indicator light diode mod
          - LED underglow kit
          - Aftermarket LED headlight bucket
          - Hex head engine case bolt kit
          - SH775A Reg/Rec upgrade
          - Dynatek Dyna S ignition
          - All Balls taper bearing steering stem mod
          - Dynatek 5ohm ignition coils and NGK caps
          - Custom cafe seat

          Comment


            #6
            There's a couple of places at the front of the cylinder block crankcase suitable, to put a bolt of exactly the right length bolt with the nut and unwind it, it breaks the gasket, it doesn't take much.
            Its also worth pressure washing the cylinders very thoroughly first to stop the dirt falling in as the block comes off.
            sigpic

            Don't say can't, as anything is possible with time and effort, but, if you don't have time things get tougher and require more effort.

            Comment


              #7
              Can you elaborate on this?

              I assume.youre talking about these holes in the front? There's not much clearance there, how would I get a bolt in?

              20211008_083337.jpg
              $100 1978 GS400 Rebuild (Outdated thread, new one soon!).
              - Indicator light diode mod
              - LED underglow kit
              - Aftermarket LED headlight bucket
              - Hex head engine case bolt kit
              - SH775A Reg/Rec upgrade
              - Dynatek Dyna S ignition
              - All Balls taper bearing steering stem mod
              - Dynatek 5ohm ignition coils and NGK caps
              - Custom cafe seat

              Comment


                #8
                Originally posted by ItsBork View Post
                Can you elaborate on this?

                I assume.youre talking about these holes in the front? There's not much clearance there, how would I get a bolt in?

                [ATTACH=CONFIG]63443[/ATTACH]
                I'm not sure if it's an optical illusion but this photo seems to show a tab of sorts sticking out where you can pry up against. A piece of wood wedged between that tab and the crankcase, then lever the cylinder up to crack the gasket loose?
                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


                  #9
                  Another option is prying up on the cam chain tensioner tunnel. Use a block of wood to lift the pry point off the back of the engine.
                  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


                    #10
                    Originally posted by Nessism View Post
                    I'm not sure if it's an optical illusion but this photo seems to show a tab of sorts sticking out where you can pry up against. A piece of wood wedged between that tab and the crankcase, then lever the cylinder up to crack the gasket loose?
                    There are 8n fact two tabs there. They have a hole through them, I assume to hook a hoist to? The holes go pretty far up through the fins.

                    I've tried levering there a bit but there's not a ton of clearance to get anything underneath. I may try getting a couple hooks through the tabs and put a rope through them and over the frame and find a way to pull up against the frame. Otherwise I guess I'm going to be doing some more whacking this weekend.

                    I assume the top of the crankcase is pretty thick and I'm probably not going to punch through it levering against the cylinder.
                    $100 1978 GS400 Rebuild (Outdated thread, new one soon!).
                    - Indicator light diode mod
                    - LED underglow kit
                    - Aftermarket LED headlight bucket
                    - Hex head engine case bolt kit
                    - SH775A Reg/Rec upgrade
                    - Dynatek Dyna S ignition
                    - All Balls taper bearing steering stem mod
                    - Dynatek 5ohm ignition coils and NGK caps
                    - Custom cafe seat

                    Comment


                      #11
                      Originally posted by ItsBork View Post
                      Can you elaborate on this?

                      I assume.youre talking about these holes in the front? There's not much clearance there, how would I get a bolt in?

                      [ATTACH=CONFIG]63443[/ATTACH]
                      Sorry this isn't how i remember these at all, is there nowhere at the back of the block? Once you have a place to point load from it goes really easy, it's just that initial crack. You're going to have an unenvious job scraping gaskets off.
                      sigpic

                      Don't say can't, as anything is possible with time and effort, but, if you don't have time things get tougher and require more effort.

                      Comment


                        #12
                        Originally posted by ItsBork View Post

                        [ATTACH=CONFIG]63443[/ATTACH]
                        Back in the day Suzuki made a special tool for lifting the blocks, I was trying to find an image on google. It consisted of two flat blades of aluminum that is pivoted at the handle end with a cam that levered the block off, it wedged into the place you have shown.
                        sigpic

                        Don't say can't, as anything is possible with time and effort, but, if you don't have time things get tougher and require more effort.

                        Comment


                          #13
                          Get a chunk of wood or something and jamb in into that space and lift up.

                          BTW, if you thought getting the block off was hard, wait until you try to scrape off the base gasket!
                          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
                            Originally posted by Nessism View Post
                            Get a chunk of wood or something and jamb in into that space and lift up.

                            BTW, if you thought getting the block off was hard, wait until you try to scrape off the base gasket!
                            Got any tips for this? I know to stuff rags inside the crankcase to stop crap from falling in there and I know not to scrape too hard and risk marring the surfaces but is there any other advice I should know?
                            $100 1978 GS400 Rebuild (Outdated thread, new one soon!).
                            - Indicator light diode mod
                            - LED underglow kit
                            - Aftermarket LED headlight bucket
                            - Hex head engine case bolt kit
                            - SH775A Reg/Rec upgrade
                            - Dynatek Dyna S ignition
                            - All Balls taper bearing steering stem mod
                            - Dynatek 5ohm ignition coils and NGK caps
                            - Custom cafe seat

                            Comment


                              #15
                              The old style Permatex gasket remover was okay. The new Low VOC stuff is junk. Some people use high strength paint stripper. Goop it on and wait half and hour and then scrape. You will only get off a small layer at a time. It will take a number of layers so you have to just accept the pain and don't rush.
                              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

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