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Started on the magneto for the 1938 Johnson MD-38 and
find that the coil’s secondary winding is “open”
Anyone tried an OMC coil swap on this type magneto before,
and succeeded?
Prepare to be boarded!
Decided I wouldn’t be out much to destroy a bad coil, so I knocked the guts out of it.
It all came apart easy.
The inner core, cleaned up..
The laminates separated..
OMC type coil too big around 🙁
Prepare to be boarded!
Had this “Military” specs Scintilla type coil in the cabinet for a rainy day…… or
a 37 degree sunny day, in this case. It’s the same diameter as the original
Johnson coil, and close to the same length.
Removing the laminate core from the Military specs coil fought me the whole way.
I had to cut off some of the laminate pieces on one end, then start driving them
out with a punch. The punch kept binding up. I ended up switching to using
the tang of a small flat file, which I had to grind down some to make the tang longer.
I finally got the core out, and the coil still test okay on the ohm meter!
I was hoping to be able to use the laminates out of this coil, and just add the
center piece from the original coil, that has the mounting holes for the mag plate,
but that option went out the door when I got out the hack saw. I’ll have to grind
down the original coil laminates to fit, but I had enough fun for today!
Prepare to be boarded!
The PM picture I sent
is about this substitution.Tubs, if you’re talking about the photo cropped together of the mag plate and
Lockwood lower unit, I’m still not sure what coil you used.Looks like you had to grind a little off of the coil case…..
how do you know how much you can grind off before it’s too late?Prepare to be boarded!
I got the military specs coil mounted today, and after these photos were
taken, soldered on the spark plug wire. Also test fitted the flywheel for
clearance around the coil. I “think” it will be okay, but hard to tell until
the powerhead is fully back together.Now, I’m wondering what mfd cap or condenser I should use
for this coil? Can I assume / hope that the rating would be the
same as a singe cylinder Mercury using the Scintilla coil?Thanks.
Prepare to be boarded!
Some of the conversion was easy, and some I worked way harder than
should have been necessary!
Got the rest of the mag together today. I ended up cramming two .1 mfd
caps in an old condenser can, mounted where the original condenser was.
That reminds me, I need to order some .20, or .22 axial caps again.
I got rid of all the soldered wiring joints, (as they were like the MS-38
shown) coil to points, condenser & kill post, which will make taking it apart
easier, if needed in the future, like if my conversion doesn’t work!
Also put the powerhead back together today, which brings up another issue,
but I’ll start a new post for that.
Prepare to be boarded!
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