1927 Johnson A-35 Ignition Coil – What to do?

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  • bayham3261


    Replies: 52
    Topics: 10
    #178258

    Hi Everyone, I just pulled apart a Johnson A-35 and everything appears to be in very good shape except no spark. All of the wire insulation was decomposing before my eyes. The points look salvageable and I extracted the ignition coil from the magneto plate. The coil is giving me some poor readings so I would guess that it is unusable- extremely low resistance. Does anybody have the correct ohms for the primary and secondary on this coil? I’m not looking to invest in a coil rewinding yet… maybe in the future. Are there any coil substitutions? I’m also thinking of building a buzz box and running it off of this for now. Any suggestions? Thanks!

    A little information is a dangerous thing!


    Tom

    US Member - 1 Year (includes $3 online payment fee)
    Replies: 636
    Topics: 57
    #178262

    Primary should be around zero. Secondary is about 9000 ohms (9 kohms). Unlike other coils which fire one cylinder only, this one fires two cylinders at the same time. The secondary is not connected to the primary. To test the secondary, you need to measure across the two secondary terminals, NOT from one high tension terminal to ground or primary.

    T


    jeff-register

    US Member - 2 Years
    Replies: 1564
    Topics: 54
    #178263

    Tom is so correct!
    The winding either sec or primary has just two ends per winding. The secondary winding in this case both ends of the winding both go to the spark plug outputs or hi-volt leads.
    Electricity looks for the easy path to ground, in this case the spark plug gap. There are differences of resistance which the one with the least will arc to ground providing the winding energy still saturated firing the second spark plug. If you had only one spark plug it’s possible to ground one hi-volt to produce twice the energy. 50% less resistance = 50% more voltage.


    bayham3261


    Replies: 52
    Topics: 10
    #178265

    Thanks! So i think i must have misunderstood my multi-meter and how to measure this type of coil… I quickly drafted up this diagram of my readings.

    IMG_4885

    A little information is a dangerous thing!


    jeff-register

    US Member - 2 Years
    Replies: 1564
    Topics: 54
    #178284

    That looks great! No direct electrical connection between primary & secondary. Should read infinite. Get a magnifying glass & look for little bumps on the exterior of the coil. If it was turned over while the plug wires were off, it has now created energy & needs to go somewhere & sometimes arc to ground thru the coil close to the mag plate making small openings on the exterior of the coil. If replacing the plug wires clean your soldering tip well while hot then melt or tin fresh solder to the tip. Reason why is liquid solder transfers heat faster so the original solder joint melts faster & can get the heat off the coil terminal faster giving you better chances of no damage to the coil or terminal. Just like boiling potatoes in H2O, heat transfer is all. P.S. use a wet sponge while prepping the tip.

    • This reply was modified 4 years, 9 months ago by jeff-register.

    The Boat House


    Replies: 4550
    Topics: 111
    #178287


    bayham3261


    Replies: 52
    Topics: 10
    #178296

    Thanks everyone! I’m going to try reusing the old coil and if it doesn’t work I’ll give the substitution a try. Thanks again!

    A little information is a dangerous thing!

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