Re: Problem with substituting OMC coils in an antique

[George Emmanuel]

Hey Jeff,

I’ve done substitution of old coils before with great success, and it is probably because they all were made similarly, but this was my first venture using OMC style coils. I have no idea of the design of the internals on the old coils that fire 2 plugs at the same time, but what you said gave me insight. I know a bunch of folks have been using the OMC style coil and doing mods, and this was my first. I have another Caille just like the one I am working on that I did years ago that had the Eisemann mag with a dead coil. On that one I had a spare Bosch magplate (Caille used 2 different mags on the same engine) from another Caille that I adapted. I took the coil and heels off the Bosch, mounted them on the Eisemann mag and set it up in the lathe and re-cut the heels to fit, and it worked great! But here’s a twist, the serial numbers on that motor and the one I’m currently working on are 200 apart and there is about .015 difference in the bore of the mag plate! Both are Eisemann! Go figure! There is a significant difference on the bore of the Bosch vs Eisemann mags and Caille top main bearing boss.

"Remember the primary & secondary windings are already bonded together as only one ground emitts from the coil except old johnson coils have a ground wire for both windings." That is the part I have difficulty understanding. If the secondary is "bonded" to the primary, there is no difference in the resistance going from what I’d call left to right in the primary,–and that is where this issue of what I described as reverse polarity causes me confusion. Keep in mind, I’m a hobbyist with limited electrical/physics background.

The good part is whatever I’ve done works! And if I do it again or help someone trying the same thing, I can lend some experience! And the sharing of experience of members like you is what makes the club valuable!

George