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MG TD TF 1500 - Original ignition coil repair

My original date coded coil from TD-4834 has been in dry storage for the last 6 years of ownership and was not in use for 40 yrs prior to that. I recently noticed that the coil has sprung a leak where the can mates to the “top”. The can is intact with no visible corrosion present. Can the coil be saved? How? Does somebody do this kind of repair? What is the oil used? I see the soldered hole used to fill it in the bottom of the coil. I’d like to save it if possible just to keep it functionally intact and with the car. Since I have other original coils for the MK IIs I own I would like to insure their survival as well.

Bill Chasser
TD-4834
W A Chasser

Google, lots out there
George Butz III

I am skeptical on these coil repairs and am also not certain how you can test them other than driving the car.

I have my original coil and it looks fine and tests OK based on all the tests I could find on the internet, but it performs poorly in the car.

So if anyone finds a definitive way to test and or repair these coils, mine will set in the closest waiting it's day.

BTW the reason you want an original coil is that it is date stamped on the bottom and can be clearly scene by the discriminating viewer.
Christopher Couper

I don't have a definitive answer either, but I'll hazard a solution. Effecting a seal between the can and the top could take no more than a smear of adhesive all the way round. Degreasing first is obviously necessary - at first I thought epoxy, but cyano would be even better solution as it would penetrate the gap. I guess that if the oil loss is small, its going to not matter, the oil is there, I presume, as an insulator and a heat transfer medium. If the oil loss is major, then you might want to consider topping it up through the original hole with a hypodermic. Type of oil? Well seeing its from the 1950s, the core of the coil wil be protected with paper and shellac or traditional varnish for which the solvent is alcohol. This would be resistant to mineral oil, so that is what I think it is, of a fairly low viscosity, which would be desirable to push through a hypodermic anyway. The oil shouldn't attack the varnish, which is what matters.
Dave H
Dave Hill

Mineral oil was used for most coils.

I would also be interested in the proper way of testing these. I have a old penski car analyser and it has instructions for testing a coil. Is there a difference in our old coils?

Bruce Cunha

A standard T type coil will have a resistance of about 3ohms, whereas a later ballast coil (MGBs, etc.) will have a resistance of about 1.5ohms, So I imagine your tester will have different settings for each. Modern coils are probably completely different, I don't know.
Definitely mineral oil in those old coils, not transformer oil or some other nasty that some have proposed from time to time, so attempting a fix should be possible with safety.
Dave H
Dave Hill

Thank you Dave for your comments regarding oils and the resistance specs that Bruce inquired about. I will look into this further when I get back from GOFWest and report back. I was really hoping some one would provide this service so I could send it out and save the coil. I was concerned to some extent as to whether there would be PCBs to worry about if I were to open the coil up I’m assuming that the oil level would have been filled to capacity during its production. The coil was good when I tested it several years ago but will certainly put my multi tester on it and check it again. My MK II coils are different than than the std coil I have in the OP and would like to insure that they will hold up for the duration of my stewardship. I’m am really surprised that the coil started leaking in dry storage.

Bill Chasser
TD-4834
W A Chasser

This thread was discussed between 01/09/2018 and 06/09/2018

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