HD-15 Johnson Magneto

[Buccaneer]

I got the HD-15 power head buttoned up today after putting in new
rings, etc., so I tore into the magneto.
To check the coil ohms, is it correct to test across the two
secondary post? If so, I got a reading of
6.4 k across the secondary leads, and .1 across the primary.
Sound about correct for these coils?

I’m tempted to clean the rust off the laminates.
Were these 1940 components made of special metal,
or have a coating that I should not remove?
If there was a coating, I can’t believe there’s any
left being rusty and all. I could sandblast them
or wire wheel them. Advice?

The "secondary" wires join the spark plug wires
at the "grounding" brushes where they are
soldered on, what I presume is a tab off the
thin brass cylinders the grounding brushes
go into.
How "delicate" is this joint? I hate to destroy
the brass tower or connection while un-soldering
the plug wires and re-soldering the new ones one.
To get the mag components off the plate, I just
"snipped" the plug wires off for now.
Thanks!

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Prepare to be boarded!

[garry-in-michigan]

That sounds about right for that coil. The coil laminations are painted with a non conductive paint to hold down eddie current which can heat the coil and lower efficiency. Yes, use care in soldering as those tabs are not very robust. . . 🙂

[1946zephyr]

Agreed on soldering new wires on. Concentrate a little more heat, on the spark plug lead, then the last couple seconds on the coil connector, just until the solder pulls itself on it.

[Mumbles]

These tubes never had a tab on them, only a drop of solder in the cutout holding the wires on. Yours might be different though as my mag had been worked on previously. Your soldering iron or gun up to full temperature should make quick work of the joint. Just make sure no molten solder gets inside the tube as the brushes don’t have much clearance in there to begin with.

I buffed all of my lams with a wire wheel before painting them while stacked up and it doesn’t seem to have affected the spark in any way.

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[Buccaneer]

Thanks for the replies fellas.
I have a bottle of "high voltage, clear liquid" "stuff" that
I’ve used on cracked coils in the past. I wonder
if a light coating on the outside of the laminates
(after they’re cleaned) would help keep "Eddy" away?
Perhaps, if nothing else, it would slow down any
rust, as would paint.

Prepare to be boarded!

[Buccaneer]

Finished up with the magneto this morning (I hope)
It was a lot of monkeying around trying to get
everything to fit. I like the idea with using
the brass bar from a later HD-25 point set
so things could be "un-screwed", instead of
"un-soldering".
Used some Super Corona Dope on the coil
and liquid tape on a few spots. Should
be as good or better than all the original
"black crap" all over!

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