Home Forum Ask A Member 1940 Johnson HD-15 Magneto testing

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  • #7421
    Buccaneer
    Participant

      US Member

      Now that I have a Steven’s ST-75 tester, I decided to pull
      the magneto back off the troublesome "subject" Johnson.
      This is the video I took a while back of it running
      very erratic.
      https://youtu.be/aPybyPCCht8

      I believe I got the twin cylinder "one coil" system
      hooked up to the tester correct, as it made spark!
      I grounded one plug wire to the mag plate, and hooked
      up my "secondary" lead to the other.
      Primary tester leads hooked up normally.
      I tested twice, grounding the different plug
      wires to the mag plate, and both times it
      made steady spark at around 2.6 amps.
      ===========================================
      Update- I just found the "specs" for this coil and
      it say 2.5 amps, Reverse Polarity. I had
      it hooked up normal polarity, so perhaps
      it would have sparked at a lower amperage
      if I hooked it up correctly. 🙁
      I can retest tomorrow, but not sure what that will
      prove as I didn’t find any arcing / leakage before.
      =======================================
      I then used the leakage "probe" and didn’t find
      any obvious leaks, but if you got the probe anywhere
      near the top near the top of the ground brush towers,
      she’d arc nicely from the brushes!
      I did get some "tiny, tiny" arcs from around
      the tower mounting screws, but this appeared to be
      some kind of inductance spark like I noticed on
      a different coil.
      I see no carbon tracking on the flywheel bakelite grounding
      plate, and I have cleaned it twice before with electrical contact cleaner.
      The coil checks out on the Ohm meter at .1K primary, and 6.38K secondary.

      I guess I’m kinda at a loss of what to do next.
      From the video, does it sound like an electrical problem?
      Thanks for your thoughts!


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      #60267
      joesnuffy
      Participant

        You might want to insulate your capacitor wire with some shrink rap where it hooks up to positive side of coil. Also what type of capacitor and value are you using? Should be like a .09 – .125 shouldn’t it?? that’s way lower than the .2 or .22

        Joe

        #60271
        Buccaneer
        Participant

          US Member

          Joe, it’s been a while, so I have no recollection on how
          I chose to use that .2 uf capacitor. I may have checked
          the capacitance of the original, been steered to using
          it, or just plain didn’t think about it!
          Not sure if I have the original in the photo to check,
          but will look tomorrow.
          I see the parts list calls for a 71-1555 condenser.
          I doubt if that 1940 parts number is going to help!
          Would a "wrong" capacitance cap cause a motor
          to run that irratic?
          Should I be putting shrink wrap on all those orange
          caps I use?
          Thanks for the ideas!


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          #60273
          Buccaneer
          Participant

            US Member

            I think this is how I came by using a .2uf cap
            for the HD-15. This table says .18


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            #60274
            joesnuffy
            Participant

              I just put shrink rap on the leg of capacitor that goes to the points. When that baby is running producing max voltage who knows might be making it miss? They insulate the condenser wire.

              I know most the time the condenser value is married to the coil used. I can’t say that’s your problem but what if it is. I was looking at the condenser chart for a 1940 – 1941 Zephyr it runs a similar coil and it was showing .09-.125

              I hope that helps,
              Joe


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              #60275
              Buccaneer
              Participant

                US Member

                Found a member’s video of a HS-15 Johnson running.
                Here’s what they’re suppose to sound like, lol
                https://youtu.be/EkwokfkpGs0

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                #60282
                joesnuffy
                Participant

                  Found this other thread here on our forums.

                  viewtopic.php?t=10117

                  "Can someone explain the theory in detail on how this point setup works with the carbon brushes? Found a .18 mfd condenser but still can’t get it to fire."

                  Then Response

                  "I’ll be daring and give it a try. You have an alternate firing two cylinder with the coil from an opposed twin. Testing the coil is done like an opposed twin where you test across the plug leads if you have the flywheel off – not lead to ground like a normal alternate firing twin. When everything is working the brushes ground alternate sides of the coil. To do that on the underside of the flywheel is a bakelite disk for an insulator. There are grounding points in it. The brushes make contact on each side and provide the alternating spark. The brush holders have to be clean and provide insulation for the brushes and there has to be contact through the grounding points with the flywheel. Once everything is clean and correct magic happens.
                  Did that help any? Experts don’t be afraid to jump in here."

                  Here are my thoughts below:

                  Watching your video when you tried to ground each plug it was like no real definite reaction like a cylinder that isn’t firing seem like both weren’t firing evenly their firing sporadically or one is double firing.

                  Have you checked the flywheel bakelite for cracks. Possibly rig/attach like an omc high tension side coil wire to flywheel using your stevens meter and check it all around bakelite for arching with your probe?? Also check the metal ground point on flywheel for arching I am guessing it should arch in that spot??

                  Thinking to myself what I would do. What if you use a timing light on engine. With magneto in a fixed position where motor will run. Make marks on flywheel and engine for both cylinders where points open so with the light you could see if while its running if your getting double fire on a cylinder instead of single fire?? You could make the marks different colors or a big number 1 and big number 2. If a cylinder is double firing that’s a brush problem but it might help you identify which brush. Also if its double firing the brass tab in flywheel might not be grounded correctly the stevens meter probe test should tell if it is or not.

                  Joe

                  #60283
                  Buccaneer
                  Participant

                    US Member

                    Joe, thanks again for your thoughts.
                    I seen that other thread and glad to
                    see I’m not the only one ever having
                    troubles with this type of mag!

                    When I was grounding out the spark plugs
                    (in the video) I didn’t get the reaction one
                    normally would, but if I remember correctly,
                    the reaction seemed "more normal" when
                    shorting out one cylinder than the other.

                    I’m not sure "how" or "if" the Stevens ST-75
                    could be used to Hi-Pot the bakelite
                    plate in the flywheel. I’d really be bummed out
                    if I fried my new found Stevens 😮
                    Anyone have thoughts on if it’s "doable?"

                    Joe, regarding the timing light, that’s an interesting idea.
                    Being that there’s only one set of points, I would think
                    theoretically, the timing between cylinders would
                    be automatically synced?
                    I guess I could use my "buzz box" on the points (if I can snake
                    a wire up through the bottom of the mag plate) and mark
                    a spot on the flywheel for the top cylinder where the
                    buzz box sounds off (points open), then do the same
                    for the bottom cylinder, as you say, using different color
                    markers.
                    If the plugs are indeed firing between "top dead center" of
                    the piston strokes, the timing light should be flashing
                    in places other than "on" the colored marks, and I might
                    break out in a disco dance?
                    Is this the general idea?
                    I think my old Sears timing light still works….. guess it’s
                    worth a try if I can get the HD-15 started again!
                    Thanks for the ideas!

                    Prepare to be boarded!

                    #60285
                    joesnuffy
                    Participant

                      With rigging up the flywheel take a omc coil and a piece of plug wire put one side of plug wire into omc coil like normal on the other side ground it to your flywheel. Note: flywheel is off engine sitting on work bench. Then hook up omc coil like normal to stevens tester and use the probe to go around checking bakelite and brass tab for arching. Bakelite shouldn’t arch tab should ark. Does that make sense or am I off base on that.

                      I am guessing you got 2 lobes on the cam that opens points. Thats how I would make my marks when the points open for each respective cylinder. You are right in what I am thinking timing isn’t the issue but double firing might be happening that is what I think my test might determine

                      Joe

                      #60290
                      Buccaneer
                      Participant

                        US Member

                        Joe, I think I understand your "hook-up" for testing
                        the flywheel bakelite with the Steven’s probe.
                        I drew it out on a piece of paper and think it could
                        work. Maybe I’ll upload a drawing of said plan
                        later.
                        I’ll have to look at the cam, I can’t recall if it has
                        to lobes or not.
                        Gotta go walk the dog between rain showers!
                        Thanks!

                        Prepare to be boarded!

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