Problem with substituting OMC coils in an antique

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  • george-emmanuel

    US Member - 1 Year (includes $3 online payment fee)
    Replies: 498
    Topics: 36
    #2107

    This has me baffled:

    I modified a Caille mag that had a bad Eisemann coil. The Eisemann is the one with the tiny rods for a core with an anchor screw that passes through the core to anchor the assembly to the shoes. So it was easy to make the mod using 2 new OMC type coils. I simply removed the rods from the old coil, made a delrin spacer to fill the gap in between the two new coils after taking measurements to achieve a final fit between the 2 shoes, and then inserted the rods and the anchoring screw into the coil assembly until I had a tight fit. (This is a procedure that has been written about in the Outboarder magazine).

    Once assembled the new coil was mounted onto the shoes via the anchor screw and then mounted to the mag plate. The new coils have a black and green wire going to the primary windings, so I attached the green ones to the points/condenser and the black ones to ground. This supposedly makes the coils wired parallel. I made sure the points were not making contact by putting a piece of paper between them and then I did a battery test and no spark. I then tried the wiring in series with one coil’s black wire to ground, its green wire to the other coil’s black and the other coil’s green wire to the points/condenser. Still no spark.

    I decided to do a test of each coil and in order to do so I returned the wiring back to parallel with both black leads to ground and separated the greens so I could fire each coil independently. When I fired one coil it made the other coil fire. If I removed the ground (black) from the coil not being tested, only the coil being tested would fire and that was correct.

    Then I thought maybe on some fluke there might be a polarity difference between the 2 coils, so I did the 2nd paragraph’s procedure again but with reversed polarity and still no fire.

    I realize that using the battery that I’m creating a magnetic field in the core, but how could that cause the other coil to fire if only 1 primary wire is grounded? Is the voltage created by one coil sufficient to fire both coils? I have not tried the mag on the engine with both coils wired. Perhaps that is the missing link in this mystery as with the battery I’m not creating the typical magnetic field. Have you folks got any thoughts? Have any of you done the OMC coil trick? Am I doing this correctly?


    jeff-register

    US Member - 2 Years
    Replies: 1564
    Topics: 54
    #20852

    George,
    When you fired each coil with the green lead disconnected from one coil it would make which coil fire? The grounded or non grounded? Thinking current reverse. The other coil still is seeing a voltage spike to fire.


    mercuryman


    Replies: 467
    Topics: 167
    #20856

    Try mag. on engine and ground plugs.


    george-emmanuel

    US Member - 1 Year (includes $3 online payment fee)
    Replies: 498
    Topics: 36
    #20862

    Thanks for the suggestions! Since I posted the issue I went to my shop (I was working on the mag at home) because I could only do a battery test at home. Once at the shop I went through the same procedures and I could only get one plug to fire using the flywheel, and that was with both grounded and one green wire off. The coil with the green wire attached would fire and it did that on the other coil if I disconnected the previous and connected the other. But if I attached both green wires it would not spark. So off came everything and I tried parallel and in series wiring with no results.

    Now I might add that these coils are NAPA and previously coils I got at NAPA (Sierra) were made in Germany,—now they are from China! I can’t wait to see Outboard Jim @ Tomahawk to stock up! So being persistent I thought maybe there could be a polarity issue between the green and black wires, and sure enough when I wired the mag in parallel as before but switched to one green and one black to ground and the other green and black to the points HOT FIRE!!

    So now I’m wondering if the issue is reverse polarity (improper winding in the coil) (hecho in chino) or does having the same polarity between the coils cause a cancelling of the magnetic field? Does trying to use a battery also affect the magnetic field? At any rate I’ve got a clean job and hot spark.


    jeff-register

    US Member - 2 Years
    Replies: 1564
    Topics: 54
    #20869

    George,
    On your motor are we looking for both coils to fire together? How about the stock coil had only one primary winding correct? If now with two coils on the same lamination we must convert two primary windings into one winding so both coils fire at the same time. I’m thinking to tie the two primarys together some how in series. Remember on the double coil there is no ground it ties to the center tap of the coil. I believe that is the key is to tie the primary ground to the other coil ground not touching motor ground. Just think one winding using both windings in series not grounded. 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. Take the ground from the first coil & go to the mid point winding on the second coil then ground the ground wire. Keep the mid to ground connection isolated from metal. Trying to load up both coils at the same time in series. Educated guess. Two old Johnson coils would be easier.
    Have you thought of the cap? It may need to be doubled too for twice the windings.


    george-emmanuel

    US Member - 1 Year (includes $3 online payment fee)
    Replies: 498
    Topics: 36
    #20870

    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


    joecb

    US Member - 2 Years
    Replies: 906
    Topics: 92
    #20874

    This may be far fetched, but have you tried flipping one of the coils on the core. I’m thinking about the old Physics class "right hand screw rule" for the relationship between current flow in a winding and the direction of the magnetic flux…. (if my foggy memory serves). The coils may be canceling out each others magnetic flux.
    Joe B


    jim-moffatt

    US Member - 2 Years
    Replies: 225
    Topics: 33
    #20876

    George
    THe coils were originally designed for single cylinder use. In this case the polarity of the coil is of no concern and either polarity will work as well as the other one.

    When they are both installed on one core they will not fire if their polarities are opposing. this is exactly what you observed.

    A final caution – for best results both coils should be as identical as possible. This is to insure the voltages produced by them are as nearly equal as possible. They will work with some voltage imbalance but I suggest you get two coils which are identical.

    Maybe the wires were installed on one of the coils incorrectly. See if both green wires come out of the coils at the same side relative to the spark plug wire.


    george-emmanuel

    US Member - 1 Year (includes $3 online payment fee)
    Replies: 498
    Topics: 36
    #20878

    Jim and Joe,

    Steve Wood called me and said basically what Joe said about how the coils face each other. Yes, both coils were purchased together and appeared to be identical, but what I can say is it was interesting that out of the 4 lugs on the primary, one was smaller than the other three, which I guess is Chinese quality.

    Curiosity has always been my driving force and it has made up for a lot of ignorance! This was a fun project. The reason I could not have the coils facing the same direction was due to the location of the plug wire terminal. If I had them both in the same direction the cam would rub on the plug wire terminal on the coil.

    Thanks for sharing knowledge!

    George


    jeff-register

    US Member - 2 Years
    Replies: 1564
    Topics: 54
    #20886

    George,
    The coil is basicly a transformer. You proved this with voltage. Figure each coil having two coils of wire. Two windings have 4 ends correct? Now the primary winding has one end go to the points, the other end of the primary winding goes to ground & also goes to the secondary winding end. The other end of the secondary winding goes to the spark plug.
    What I was trying is to tie both coil primary windings together so when the points set contact set opens both coils would see the spike & cause both coils to fire.
    The two cylinder coil only has one primary winding & when the points open the one primary charges the one secondary coil. Difference is the secondary coil is isolated completely from ground. Both ends go to plugs. When one plug fires it sees a ground & the second end of the secondary still has enough energy to fire the second plug.
    What you are trying to duplicate is built totally different windings & taps to the ends of each coil. I was trying a way to tie the primary of both coils together to get the coils to fire together. Hope this helps, No formal training here, Just Jeff reading.
    P.S. If you have a sensitive ohm meter the ground terminal wire to ground should show .5 ohms at the most. The primary winding has very little resistance.
    Jeff

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