MTFCA Forum

I am attempting to recharge my magneto magnets, which I've successfully done in the past for this engine, with each magnet capable of supporting a 2 LB steel weight. But last summer, the cutout failed, and afterwards the magneto barely worked. I've seen other posts implying that a shorted cutout could apply a DC voltage across the coil ring, discharging the magnets.

The engine is out now, but I have not disassembled the flywheel, not wanting to go through the trouble of resetting coil clearance. So I with the hogshead off, I positioned the flywheel where the magnet to the left of the pickup post was North and the one to the right was South, and applied 24 vdc (2 12v car batteries) with the positive lead to the pickup point on the coil ring.

I flashed it a half dozen times, but the magnets still won't even pick up a nail (they will pick up steel filings & tiny things). I can tell the flash is happening, because of the large arc and the thunk made as the coil ring tries to bend to reach the flywheel (I have a wooden shim in place to limit the ring movement and try to avoid cracking it). I did try rotating the flywheel 180 degrees, to no effect.

There is no measurable difference (I don't have a gauss meter). I could barely determine the polarity, they are so weak. But even if they were backwards, wouldn't they all eventually recharge the other way?

FWIW, the resistance on the mag coil is about 1 ohm, the same as it was when it worked, getting similar numbers with both a Fluke 77 (digital) and a Simpson 260 (analog). I have 4 other mag coils that all measure between .7 and 1 ohm, including one that is known to be working. The 'correct' number I have seen is .25 ohm, but I'm suspicious of accuracy at these small numbers. Also, the ring clearance is between .025 and .045 all the way around (a little wider than I would like, but only on 3 coils).

Any advice? I want to get this engine back in next week for what is left of touring season.

Thanks,
Stan

beth wrote: ↑

Mon Jun 16, 2025 12:55 am

...the cutout failed, and afterwards the magneto barely worked. I've seen other posts implying that a shorted cutout could apply a DC voltage across the coil ring, discharging the magnets.

That really should not be possible.

Since the engine is out of the car, it would be best to take the magnets off the flywheel and magnetize them individually.
I agree with Jerry, it is not possible for a shorted cut out to do anything to the magneto.

There's no need to remove the individual magnets. Lay the transmission on plastic 5 gallon bucket, magnets up. Lay a good mag ring on the magnets in the correct orientation using a compass. Clip the ground lead of a MIG welder onto the cast frame of the mag ring. Then very briefly, zap the MIG wire on the blob of solder. I watched Dennis Newman do this a couple weeks ago. It works perfectly, and only takes a second.

That's risky to flash on the lead button. Hard connect to the solder & flash ground on the ring.

Sounds like the polarity is backwards.
I have seen this when the north south is reversed.
Just swap the + and - leads and try again.
Also striking the ground lead like a welding lead may help.
I see best results with 3 batteries, 36 volts.
Good luck.

To OP.
I test the field coil with a 6v battery charger as a power source. Run a compass around to each coil. There should be alternating N & S readings all the way around. Mark the polarity on the coils for later use. That tells you all the coils are all conducting without a short to ground. A second test, with the same power source is checking magnetic strength with a hacksaw blade. Pull should be consistent proving coils are not weak from internal ribbon shorting.

Using 2 12v batteries isnt enough on a full flywheel & an air gap. 3 or 4 12v batteries will generally work, but wont provide a saturating charge.

The best charge comes from a highest amp setting from a DC welder, as Ed B. suggests. This will saturate the magnets with ONE strike in car with the poles lined up. With the flywheel & field coil out & layed a top each other, without the air gap, all the better with no pull on the field coil.
Hold the positive probe to the lead button firmly & strike ground on the field coil body. Such a jolt will permanently change the magnetic polarity if not charged the same. Dosent matter.

If you want to charge in the same polarity, note & mark the coils what you found (N&S)in the first field coil test. Use your compass around the magnets on the flywheel to also find N&S polarity. Lay the field coil on the magnets N on S & S on N poles for the charge.

I use an old Golf Cart Battery Charger that used to charge six 6-volt batteries.

It puts out 40 Volts DC and $0 amps DC or a little less if the Mag Coil Ring measures more than 1 Ohm.

The Timer was changed to push button and three 5 second Zaps does a full charge.

Laying the Mag Coil Ring on the Magnets, with the transmission assembly sitting on a 5 Gallon bucket will let me pick up the Coil Ring and the transmission will still be attached.

Back in the vehicle I just did, this will provide 11 VAC at Idle and 22 VAC at 25 MPH.

I charged my magnets in 2010 and they are still going strong. I documented my success. Check out: www.mtfca.com/discus/messages/118802/159978.html.

speedytinc wrote: ↑

Mon Jun 16, 2025 8:36 am

That's risky to flash on the lead button. Hard connect to the solder & flash ground on the ring.

Thank you. I thought the same, until I saw it happen. Zero damage to the solder blob occurred.

Has the coil ring itself looked like having any damage to the coils or the coil strips between the 16 coils?. Use a analog meter to test continuity first on the whole unit and then for each individual coil.. there may be a break between one or more of the 16 coils on the magnito ring.

The first question of interest: Did the Magneto ever work?

The one I posted above that produced 22 AC Volts at road speed didn't work the first time because someone had patched the Mag Coil Ring with two wire coils that belonged in the other places.

Going around with the compass noted the Mag Coil was NSNSSSNSNSNSSSNS.

A rebuilt Coil Ring fixed the problem, thanks to Bill and Deana!