Help wanted with Vintage FM Coils

I have several Fairbanks Morse coils that came out of type fm and fmk magnetos. They are made of the cloth and varnish construction. They have been tested with a Merc-o-tronic 98 and meet specs.

My question is this. The exterior covers are deteriorating. Should I revarnish the coils or use a rubberized covering material instead, or maybe use something else?

Thanks, Joe
 
When I was a Machinist apprentice on C B & Q
railroad, we used a reddish colored varnish to
re-varnish, switch engine main generator windings.
It seemed to be the same stuff that I see on old
magneto coils. I don't remember what it was called
but it was made by DuPont. Perhaps a phone call to
a magneto rebuilder/parts supplier, such as
Branson Enterprises (www.bransonenterprises.com)
would get you some information. I scanned their
web site, but saw no special varnish listed.
 
Thanks..Dalex !
yes, Glyptal, appears to be the correct stuff,
I just "Google'd it, still available,NOT CHEAP !
 

I think I'll use insulating varnish applied under a vacuum to reseal the interior (bake to dry) then apply liquid tape to the exterior. Thanks for the suggestions.
 
I do magneto repair. I found most of the old wrapped FM coils will fail after they get warmed up. I use a old Eisemann Tester and let it run about 20 min at 1.7-2.0 amp. and then I take a heat gun and warm the coil up real good about the same temp as a mag would be on a AC tractor or Wisconsin V4. About 50-75 % of them miss fire or quit firing.
 

I actually heated the old coils in an oven @ 190 deg. for an hour before testing them. 1 of the 4 failed. The other 3 are going to get resealed. Thanks
 
That is good. That is better odds than I get. The red insulation spray I got from a electric motor shop.
Earl
 

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