Re: 1940 Johnson HD-15 Magneto testing

[Buccaneer]

quote joesnuffy:

I would clean both brush holder cylinders with that hold brushes with a small weapons bore brush like mumbles did I think he used like a 22 riffle bore brush or a brush you can spin inside the cylinder with a drill etc. The bottom cylinder especially and try to get both brush holder cylinders to have same results when you test them with meter. At this point I think you may have an issue with that particular brush for lower cylinder its having intermediate continuity with its shell. Get both insides of brush cylinder holders clean as a whistle and I think you may have a good running engine.
Joe, if I remember correctly, I used the Dremmel and round brush to clean
the insides of the tower brass cylinders, but it won’t hurt to clean them
some more.

I am also guessing their is a spring that resides under brush. Make sure to lightly sand the top and bottom of that spring with a very find sand paper like wet and dry paper.
Yes, there’s a light spring under each brush. I suppose if it were too stiff
the carbon brush would wear out fast

I am also studying your diagram. I would think the 6.38ohms should drop to zero before points break and they are not the 6.38ohms returns before points break. I wish you had a known good flywheel with bakelite and tab to test that like you just did. I will study the diagram and report back I need to look at it hard.
Electrical engineering is above my paygrade, lol
I’m not sure on the timing of the magnetic flux, points opening, etc. 😕

One question for you is when you measure between the secondaries/plug wire ends you get 6.38 ohms?? I am guessing you do. If you ground one secondary/plug wire does the 6.38 ohms go to zero?
Yes, when I measure between the two plug wires I get 6.38 ohms

Could your plug wires be backwards?? Crazy question but what if.
I wrote down that question to myself the other day, "How did I determine
which wire is for the top cylinder?" I remembered later on that Garry
mentioned to use an Ohm meter to see which wire had continuity
as the given piston was nearing TDC. Worst part is, I’m think
I tried switching wires once, but not sure!

The other thing I am thinking is that bakelite and tab is off since 6.38 ohms returns before points break. To the best of my knowledge when points break one brush should be grounded and piston grounded should be on bottom of stroke. If not I am having trouble figuring that out unless tab alignment is off or plug wires are reversed.

After studying diagram bakelite and tab could be off like 22-25 degrees or more. If you start motor and use timing light it will tell you if your getting double fire on cylinder. You may just need to spin flywheel with a rope or drill to check. If plug wires aren’t reversed I would try timing light to see if your getting double fire on cylinders and if so I would guess tab alignment.
The bakelite plate in the flywheel is held in with three rivets, so if I reset it, it would have to rotate
120 degrees one way or the other. As I posted prior, showing the link for Mumbers bakelite plate
removed, there’s a post in one spot only, for the grounding spring to contact underneath the brass
contact in the bakelite plate, so I don’t believe it’s put together incorrectly. I wouldn’t have taken
it apart to start with had it run okay.
Joe

ps I did so more thinking if brass tab is off it would only have to be off like 1/2 inch. That is not much. If your getting double fire I think that would be the tab is off a tad 3 inch diameter approximately where tab is times 3.14 (pie) times 22 degrees off divided by 360 degrees equals .57 inches or about 1/2 inch. Just thinking how much it would need to be off not much.

pss Now this is a crazy thought and I am thinking outside of box. I was also watching your motor run no recoil on it? I am guessing motor spins clockwise like most when running could I be wrong? Your diagram would make more sense if motor ran opposite direction.

Don’t scare me like this Joe, lol. Is there any outboards that run counter clockwise? It didn’t have a rewind when I got it,
but since then my uncle found an empty rewind shell. I’ll look at it tomorrow to set my mind at ease!
Thanks for all the "Thinking"
Bucc

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