I removed the engine from my recently acquired T to replace the flywheel magnets that the previous owner had removed. I found that one of the magneto coils was damaged where the starter is located. I did remove the bendix before removing the starter but either I or someone else damaged it.
But I decided to test it anyway. I hooked it up to a power supply and applied 2.5 volts dc which drew 4.5 amps; a low power level that wouldn't damage anything. I then checked for magnetism on all the coils and they all worked, including the damaged one, though at a lower strength then the others. The outer damaged coil straps looked like they are shorted together, which would effectively reduce the number of turns of that coil.
I then tested for shorts to ground. I unsoldered the ground connection and hooked up the power supply to the mag output and the metal frame. I set the current limit of the power supply to a tenth of an amp, ran the supply up to a bit over 40V and did not see any current flow. Are there any other tests that I should do?
I know that a number of members have said on the forum that once the magneto is removed, you might as well replace it. But since I'm retired, I have more time then money, so if it ain't broke, why replace it? I plan to recharge the magnets, so the fresh magnets should more then make up for the lower output of that coil.
That coil ring needs to be rewound. If it works at all, it will be weak. It can be rewound at home if you follow the instructions in the book published by the club,"Electrical System". Or you can buy one from a vendor. For the cost of the coil being rewound, it sure beats the cost of labor to remove the engine and transmission to get to the coil later.
You can get some glyptal in a spray can and re insulate it. The point others are making is that the mag coil is buried in the assembly and it's not the smartest place to pinch a penny. I think you should pinch a few pennies somewhere else and get a rewound mag coil from Wally Szumoski at Total Recoil.
According to my calculations, it would still put out over 96% output even with half the coil straps in that coil shorted together. I checked 4 venders and none sold individual coils. I could try to rewind it myself, but I would gain only 4% more output at the risk of not doing it right or disturbing something else.
Thanks, Ted. How do I contact Wally for a new coil?
773 586 4485
I think you will need to replace the unit. You can ask Wally though.
6146 South Natchez Avenue
(773) 586-4485 firstname.lastname@example.org
When I first got my 23 touting, the mag coil next to the starter looked like that PLUS the outer copper ribbon was broken with a quarter inch gap. I had the hogsheads off so I just soldered a thick copper wire across the gap. The magneto worked fine and the car ran as well as expected for old badly tuned coils. I saw some pictures of the spaghetti that occurs if the coil comes apart and following the advice of members of this forum tore it down that winter and put one of Wally's coil rings along with a set of Ron's coils in it. I don't worry now.
Robert, Wally does a very nice job on his coils, and you won't be disappointed. The way I justified replacing mine was to consider the effort to replace it VS hoping my repair would last. Like wheels and tires, some things just must be replaced to ensure peace of mind.
John S is right on about replacing the coil ring. The insulation being at least 80 years old wont last forever.
Old radiators, tires, wood wheels and old insulation eventually deteriorates.