Mag Repair

[Thorlick]

After running Rusty, my 1927 roadster pickup, on a mag expertly rebuilt by RV Anderson about 25 years ago he suddenly refused to run on mag. Generally when this happens my go to solution is an in-car mag recharge. This is actually a magnet recharge and when the problem is a short of Bat. to Mag. caused by a flakey ignition switch it always works (after cleaning out and repairing the switch). Much to my dismay it this remedy completely failed.

My second string solution is to run on battery until something more life shaking occurs. This happened about a week ago and so when Rusty started losing power and making a horrible knocking noise I decided to just pull the engine out and have a look. First try was to check the rod bearings... all was well there. Next I found the problem, a blown head gasket.

Since the engine is out now is the time to figure out why the mag is putting out a fraction of the AC voltage it used to do. After a lot of head scratching and chasing after the problem with my VOM I finally hit upon a solution... I pulled all 4 mags I had accumulated at swap meets, arrayed them on the floor and went about testing in order to find the "new" mag for Rusty... none of them were good! So the next step was to chase down where the short is. Using my 2A 6V/12V charger I energized the original Anderson rebuilt mag and chased down which coils were energized.

I was having difficulty because several poles on the field casting had developed strong magnetism over the years. After much trial I finally figured out my method. I connected the negative wire to the engine block and touched the positive to the edge of the copper ribbon coming out of the first coil. The compass told me that coil was fine by getting excited.

I proceeded to move on to the second coil, which was likewise good. Working my way around the field I was able to find one coil which was bad. In fact the mag had been running on 4 functioning coils and 12 dead coils!

Next I pried the coil gently from the field casting so it lifted about a millimeter or two. Suddenly that coil was good again and in fact the whole mag came to life! The dead mag was a short on that one coil!. So what follows is the corrective procedure I have used:

I pulled a gallon milk jug out of the trash and using scissors I made two washers as shown.

Insulator washers

The first washer is inserted between the coil and the casting.

Single washer

The second washer is placed with the slit on the opposite side from where the slit on the first washer is located.

Second washer

The mag is again tested with the battery charger. All 16 coils were now functioning so I proceeded pushing the coil back down to place with hand pressure. I again tested the mag with the charger and compass and found that the mag is now functioning as it should.

Time to get on to locating a replacement head gasket so Rusty can get back into the game!

Respectfully submitted, Terry Horlick

[Jim Eubanks]

Thanks Terry, Great work and just what I am going to have to do!

[Allan]

Terry, that's really good work. Tracking down a faulty coil in the whole stack takes some doing. Thanks for the instruction.
I would caution using plastic milk bottle material as insulation though. I think you need something which will take more heat than plastic. It could be installed the same way though.

Allan from down under.

[Thorlick]

Allan, I hope you are wrong. I gave that a cursory thought whilst doing this and decided that the constant bathing in warm oil should protect this. If it does melt I think it may remain in place with a bit of sag.

I’ll tell you what, if this fails I will dredge this post up and confess my folly! Meanwhile if anyone has a better material which is 1) thin, 2) heat resistant, 3) easily cut to shape, 4) is non-conductive, 5) has elasticity similar to a milk jug, and 6) remains in place please inform me of it.

If my repair fails I will try your superior insulating material or I will cut the bad coil out and solder another coil sourced from another bad mag.

Another option is to carefully remove the coils from one of the spare mags. And splice replacements into my current mag.

The final option is to unwind a complete mag and rewind it with fresh insulating tape.

I hope to remember to post back here in a year to report on the service life of this repair.

TH