Re: 1940 Johnson HD-15 Magneto testing

[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.

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.

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.

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?

Could your plug wires be backwards?? Crazy question but what if.

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.

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 please don’t shoot me 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.

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