Restoring Ignition Coils

Bud

Bud

Well-known member
Is it possible to restore original Model A ignition coils? Has anyone attempted doing it? My concern would be the tar or liquid inside (I have never taken one apart). If it is oil filled, is it something like PCB's which are hazardous?
Or is a strategy to remove the insides of a modern coil and put in the Model A era can? I am just curious. Thanks.
 
Bud, John Holland used to do it however the replacement coil windings he was using was obsoleted which is why he is no longer doing them.

Potting the new windings would likely not be a big deal with all the epoxies available today. Getting the Bakelite end off without damage is the part I had not figured out how to do. Jim is likely correct about the time needed and the mess!!
 
Bud - are you talking about restoring original non-working coils ?

I have three original coils that work. Continuity measurements on all three are consistent with each other and with resistance measurements I’ve seen posted online. They all work well on my Tom Wessenberg tester that simulated an engine running about about 1000 rpm.
I have one installed on my car now and plan to drive to club events.

Should I be worried about using an original coil that seems to work fine ?

Thanks. Jim
 
Yes Brent, John Holland was the man !

Conway, My experience a coil need to be gotten hot while driving to fully test.
 
Hi, I am just asking questions. I have never tackled the job. I just have a box of bad original coils and am investigating what to do. It seems a shame to junk them.
 
Bud said:
Hi, I am just asking questions. I have never tackled the job. I just have a box of bad original coils and am investigating what to do. It seems a shame to junk them.
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Do you have pics of the bad coils ? The Restoration Guidelines and Judging Standards book has much good information on identifying original coils.

The original coils are tar filled - I have had success rebuilding old radio transformers from the same era by heating them enough that the tar softens and things come apart. Never tried an original Model A coil, though. As Brent mentions, removing the Bakelite tip without damage could be challenging.

Jim
 
I am investigating what is involved. I don't want to take apart a bunch of coils and have to figure out what to do with PCB oil or how to handle the tar issue. I would like to know what the issues are before I start--if I start. Knowing about the bakelite is good. I seem to recall seeing an article on the size wire and the number of turns. I may sell the coils and forget about it as well.
 
There are 6V epoxy cased coils that have a narrow body but do not fit inside the A can.

I had one xrayed and found there was plenty of room to chuck one up on a lathe and cut down the diameter and stuff it in the can. I never got around to doing it, but that is one thing you could try.
 
jb-ob said:
Yes Brent, John Holland was the man !

Conway, My experience a coil need to be gotten hot while driving to fully test.
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True . But if you just let the coil saturate on the tester for a minute or two, it will get warmed up. A friend has a factory made coil tester, that has a warming the coil feature, and I’m guessing, but how else to heat it up in few minutes, but to just saturate it.
 
katy said:
How "hot" do they have to be?
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My coil tester has a Heat mode built in where the instructions say to test the coil first, then place the switch onto Heat mode for 10 minutes or until it feels quite warm, then test again. I will tell you that a good many Model-A coils have only a marginal spark with this tester. A modern reproduction coil be in the mid-range of the good section.

Notice in my picture below just how far the spark is jumping however also notice that range is considered poor to questionable at best. I have tested some Model-A coils that were in the good range, so my theory is many Model-As are running around with poor performing coils. If they have an engine with lower compression, they likely don't realize the lack of performance.


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Conaway2 said:
Brent - is heating a coil simply applying either 6 or 12 volts to the primary winding ?

Thanks - Jim
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I am not sure how it does it. I would think it is more about leaking secondary voltage back to a ground creating a dead-short. You can run a coil for about 10 minutes at the widest gap and the metal case will get warm, -but not hot. Flip the switch to Heat and it will get hot enough where you don't hold the case in bare fingers very long. Not 'burn you' hot, but more uncomfortable 'hot'.
 
A bad coil will have the spark gap drop significantly from cold to warm.

Good coils have a healthy spark all the time.

I loved testing coils as a kid. The spark was fun to play with and my father had be test all the coils to take to the flea markets. I tested a lot of coils and condensers.
 
Any time a coil is powered up in the electromagnet phase with no circuit breaker function, it will create heat. This is how a coil is warmed up for test. It's sort of like forgetting the ignition switch is on and the points are closed with the engine not running. Many a coil has over temped and died due to accidental ignition switch activation for too long a period.
 
One of the first things that I learned about driving automobiles was never leave the switch on when the engine isn't running . Its mostly a common sense type thing .
 
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