1950 Martin 60 Crankshaft Top Thread Broke

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  • September 16, 2016 at 12:59 pm #5270
    bjmullins
    Participant

      Hi, I was looking for advice on repair of the fly wheel nut retaining threat on a 1950 Martin 60. Evidently at some time in the past post of the tip of the crankshaft broke off and someone "repaired it" by drilling and tapping a hole in the top of the crank to put a bolt on to retain the flywheel. I don’t think they did a very nice job as it isn’t centered, also it seems rather small in diameter compared to the original crankshaft end. I figure I have several options, but I was wondering about the feasibility of having it drilled out more at a proper machine shop, then having a larger high strength stud inserted? Anyone have any experience in attempting this type repair? See pics.

      September 16, 2016 at 1:30 pm #44142
      Tom
      Participant

        US Member

        For what my opinion is worth, I would look for a replacement crank or a complete replacement block. Replacement parts shouldn’t be too hard to find, or too expensive using our on-line ads. Consider that if the crank was broken like that, someone relatively inexperienced has been working on the motor. You don’t know what other repairs are lurking. And I wouldn’t trust retaining the flywheel to the bolt that goes in that hole.

        Unless the machinist is a very close friend or an employee of yours, the cost of fixing that crank correctly, I bet, would be three or four times the cost of a replacement crank.

        Tom

        September 16, 2016 at 2:04 pm #44143
        bjmullins
        Participant

          Thanks Tom. I thought I might eventually just have to get a new/replacement crankshaft. I was hoping that I could salvage this simply on the premise of trying to preserve old parts. This isn’t a particularly nice motor, they cut the lower shroud and hacked off the fuel shut-off valve and put on one of those weed eater type red plastic fuel filter. I just don’t have a 7hp motor and wanted to make this one a decent runner as economically as possible. Appreciate your input!

          September 16, 2016 at 3:28 pm #44145
          frankr
          Participant

            Considering it is an amateur job on the crankshaft, they did a fairly decent job, even if off-center. I’ve seen more than a few done that way. Often the shaft is so hard to drill and tap. Consider just running it.

            September 16, 2016 at 5:02 pm #44146
            cajuncook1
            Participant

              Here is a link to the Martin website.

              http://martinoutboards.com/product-cate … ankshafts/

              September 16, 2016 at 5:37 pm #44147
              20mercman
              Participant

                I was going to post what Frank said. I think it is not too bad as is, and I wouldn’t want to make the walls of the crank any thinner. I would run it as is or bite the bullet and find a new shaft.

                Steve

                September 17, 2016 at 6:47 pm #44186
                bjmullins
                Participant

                  Great! It seems unanimous, just use it as is. I don’t exactly remember what type bolt/washer they used. I guess I’ll use a grade 8 hex cap bolt and a flat and lock washer? I don’t remember how much if any of the broken shaft thread stuck above the flywheel.

                  September 17, 2016 at 10:27 pm #44192
                  amuller
                  Participant
                    quote bjmullins:

                    Great! It seems unanimous, just use it as is. I don’t exactly remember what type bolt/washer they used. I guess I’ll use a grade 8 hex cap bolt and a flat and lock washer? I don’t remember how much if any of the broken shaft thread stuck above the flywheel.

                    I would probably do as you say and run it. I would also check the torque a few times to make sure you are retaining tension.

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