How bad is my mag?

[Steve Jelf]

Last year on the first day of my annual Detroit trip by 1915 runabout the magneto quit working. The car was dead in the road. I restarted on battery and drove on. Trying the mag again I found it working, but not well. The erratic dimming of the charger light showed that power from the mag was fluctuating, sometimes producing a bright light at the charger and sometimes none at all. The performance of the engine, of course, fluctuated with the light. I finished the trip on BAT. In the months since, the mag has often worked normally except for an occasional hiccup but other times with enough hesitation to make me switch over to driving on battery. I want this fixed. I imagine a bad soldered connection in the coil ring has broken loose and is making enough weak contact to produce current ranging from OK to not OK. So I see three possibilities. 1 Pull the hogshead and hope to find something easy to reach and fix. 2 Pull the engine, remove the transmission, and carefully check all mag ring connections. 3 Somebody on the forum will suggest something simple and easy to fix that I have missed.

I checked the mag post for fuzz. There is none at all.

Broken connection somewhere?

[Humblej]

Excessive crankshaft play fore and aft adversly effecting the gap between the mag ring and flywheel?

[speedytinc]

Thoroughly check around the button contact for a bit of metal grounding it out. As best you can thru the contact hole. Try an angled pick tool.
Otherwise its HH off.
With the HH off - Check for metaled fuzz making ground to the extent you can see the top half of the coil ring.
You could (carefully) with the magnets properly aligned, put power (dc) to the coil ring & check with a compass for changing polarity to catch the grounded spot you cant see. Again to the extent possible on the top half.
After that its pull the motor.

[Charlie B in N.J.]

As suggested (since you already checked the post) look for end play. Easiest. The take apart stuff comes later. Diagnose.

[kmatt2]

Steve, You may have already done this, first check, off the car, the continuity of the mag post, the mag wire to mag switch, and the switch on the mag side. Also check mag ring button as was suggested, and the mag to battery charger, it could be a bad diode. If the fault is found here it will save the work of pulling the HH for no reason.

[aDave]

All good advice has been given.....AND here's one from my experience....
My mag would quit when going into reverse. All the foregoing "fixes" were tried....no issues anywhere.
My electrician friend was genuinely puzzled becauses all the "should be problems" were not problems at all.
Out of desperation, and as a last resort, he took apart the MAG/OFF/BAT switch on the coil box (1915, same as yours), cleaned the contacts, and VOILA, problem solved.
Why the mag would quit going into reverse, I have no clue....there was NO PLAY in the crankshaft, and after "contact cleaning" no further problems.
Good Luck!
Dave

PS: Many Thanks Brad!! - and Russ, for digging into the problem!

[Steve Jelf]

I think end play is unlikely with less than ten thousand miles on the rebuild. I'll check some of the other things.

[J1MGOLDEN]

Never overlook the most obvious and most likely cause!

[Wayne Sheldon]

For whatever it is worth?
A few of my Ts I put together with functioning magnetos, I have tested mag coil rings out of the engine by connecting a twelve volt battery to them. There must be a better way, likely some sort of spring scale to get a viable reading that could be compared from one coil to the next, but I never went that far. I simply used a putty knife on each coil center and felt the pull with my hands.
On one such occasion, I began next to the contact "button", and continued around from one to the next through about eight or nine coils, when suddenly the next one had very little pull. Close examination found that the "ribbon" wire between the one that worked and the one that didn't had an odd kink in it that I hadn't noticed when working on it before. The paper insulation that was supposed to be there had a small tear in it, and the twisted kink was just barely touching the cast iron ring.
The coil ring is one long series of alternating coils, grounded at one end, and open for the electrical connection at the other end. The effect of the twisted kink was to ground the series of coils only partially around the ring. The "running effect" would be a greatly reduced voltage and current (amps) of power to run the engine. An improperly bent ribbon wire or metal contamination buildup in the oil coupled with vibration and/or temperature changes could result in an intermittent short.
It would be difficult and tricky to do? But with the Hogshead off, at least the top half of the coils could possibly be checked to try to locate an intermittent short. It would be difficult and tricky because the magnets themselves would interfere with an easy test. I have never tried to test one that way, and am not sure how I would approach it if I needed to.
Certainly, any attempt to do such a test could discharge the magnets somewhat or even almost entirely. That actually might be the best way to approach such a test? Regardless, if such an attempt was made, I would highly recommend an "in car recharge" of the magnets before putting the hogshead back on.
Another point to take into consideration, is that any testing of "intermittent" problems usually cannot be relied upon unless one can be sure it is in "failure mode" at the time of testing. Often, that isn't even possible to know when things must be disassembled in order to test them.

Good luck!

[speedytinc]

With the coil on the bench.
I test fields coils for magnetic strength as described with a piece of iron. If magnatec pull stops before the last coil it indicated a short to ground.
Next step is to test the continuity with my armature tester. 120V leads. This usually shows the weak short to ground with a bit of sparking & smoke.
A small bit of metal will burn away & clear away. The offending insulation is easily found for repair.

All that being said, in practice I replace with a new unit.
Its good insurance to a magneto failure & pulling the engine apart AGAIN.