Magneto doesn't work, what's the deal?

O

oldmotorsguy

Senior Member
I am in the process of restoring a 1917 Touring, and have added a starter to a non-starter equipped block. Accordingly, there is no generator mount and as such the magneto has to work well.

I changed the starter ring gear on a used 1926 ******, and the coil ring and magneto were intact. It is unknown whether the magneto on this used ****** worked. I had to epoxy coat a few ragged areas of insulation on several of the coils, but all in all the coil ring looked good, and was intact throughout.

I mounted the coil ring onto the 1917 block with no shims. I then bought that fancy schmancy magneto gap gauge ($200) and made sure no high or low spots were present, and mounted the ****** and checked the clearances between the magnet clamps and the coils: on top, the clearance was .044, and on the bottom the clearance was .035, to account for the weight of the ****** that would be cantilevered over a foot or so beyond the end bearing. I divided the sum of those two numbers by 2, and got .0395, which is just inside the specified max clearance in the Blue Book of .040.

When I start the engine (which fires up nicely with a new 6V battery, first time ever for this crank engine), it runs very smoothly on battery. When I measure the AC voltage coming out of the magneto post, I get a reading of only 2 volts AC, obviously not enough to power the plugs. And of course, when I switch the ignition from BAT to MAG, the engine dies.

How do I re-charge this magneto? Do magnets get too old to recharge? Is the gap clearance of .0395 too much? The minimum specified is .025, and I would have to remove the ****** again, and shim it accordingly, which entails lots of labor (not a deal killer, but something I would love to avoid). I need it at 7 volts AC or so at an idle, and a minimum of 18 volts AC when revved up to operating speed. More if I can get it.

I need to diagnose my magneto's needs somehow, but am currently at a loss. My knee jerk thought was to just yank the ****** back off, and eyeball everything one more time, but the labor involved has me a bit hesitant.

Thoughts, guys?
 
I would install a coil fired distributor on the car !! Snyders carries the complete unit, I have installed 3 so far. This unit does away with the mag and coil boxes!!!

mike
 
Should be a candidate for 'in-car' magnet recharge since you have some output and not a 'dead' magneto. A dead results ususally from a short in the field coil ring.

So here is some old instructions on doing a recharge with the motor in the car.

The meter and lamp setup is a good way to check output when you are running on battery, the lamp acts as the normal load of the 4 coils.
 

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This might sound silly but when my magneto wasn't working, turned out that my oil level was way to high, Id usually fill it up to come out of the top petcock, but now I just fill it up until it comes out of the lower one. Works perfect now.
 
Top clearance may be too wide, try the recharge first and no, in theory the magnets do not get too old to charge.
 
Mike: I have purchased three Model T's with those conversions on them (so far), and have removed all of them and restored the coil box and timer. Call me a purist. I still have one of those distributor systems in my shop, you wanna buy it? I sell it to you cheap...
 
jboggess: I have always used the top oil petcock to fill up the oil level, and have never had any magneto issues. Just for grins, I will open the lower petcock and let the oil drain to that level, start the engine and see what kind of voltage I get out of the magneto at that oil level.

If that works, I will be completely gobsmacked, as they say in the UK.
 
When setting up the gap, leave the the drums and triple gears off to save weight. The gap should be more like .035. If you had the magnets off are you sure they went back on NN SS NN etc?
I hope with all that work you used new screws. The old ones become brittle and can snap off very easily. I would have left the windings bare rather then add any kind of coating. The coating can come off and plug your oil line. I would have suggested spending the $200 on a rebuild coil ring, which may be part of the problem if it's shorted out.
 
oldmotorsguy said:
jboggess: I have always used the top oil petcock to fill up the oil level, and have never had any magneto issues. Just for grins, I will open the lower petcock and let the oil drain to that level, start the engine and see what kind of voltage I get out of the magneto at that oil level.

If that works, I will be completely gobsmacked, as they say in the UK.
Click to expand...

Well that's cool, I was just saying what i've been threw. Every Model T has a different personality. :)
 
Red: I did indeed use new screws, but did not disassemble the transmission when setting the gap. I carefully removed the magnets when replacing the ring gear and put them back the way they were. Of course, who knows if they were NN SS when I got it. Wouldn't zapping it with 50 amps change it to the correct polarity in any event? But its possible that the magnets are not correctly installed. How are they supposed to be installed, and how can I tell if they are or not? With a compass? I will probably want to know this if I have to yank the transmission back off and start over.

I've used this epoxy quite a few times before on the coils, and it has yet to come off from my observations. You would think the unravelling of the existing tattered insulation areas if left alone would be more of an oil line clogging threat than sealing them with epoxy.

Coil ring: since I get a 2 volt reading currently at idle, the coil ring is not shorted out. If it were shorted out anywhere, I would get 0.0 volt reading (dead mag), or am I wrong about that?
 
Are you checking the mag output with an analog meter across a load? If it's putting out 2 VAC then it has hope! :) Like any magnets like poles repulse NN, SS etc, opposite attract NS NS etc.
Guess 50 amps DC will ether smoke em or make em sing! Make sure you zap a couple of times not hold, then 1/4 turn and repeat all the way around. I have done the in car recharge a few times.
 
Do you have the MTFCA manuals on the transmission? This gives you all the info you need and they arent' expensive, I sell them for $11.00. You can't zap the magnets to the proper polarity, if you recharge them incorrectly the magnet is junk.

I am not a fan of the in car recharge, many people are, but it is hard on the cast iron frame of the field coil, generally it cracks them when all that voltage snaps them towards the magnets. Wally S. claims more and more of the frames he takes in as cores are scrapped out, because they don't pass a magnafluxing test.

The best way to recharge the magnets is to remove them from the flywheel and recharge them individually, this way they can be checked for cracks as well. This also give you a chance to weigh each magnet and put the same weight magnet opposite each other. But, you need several sets of magnets to do this. If you want to I always have several sets recharged on the shelf 'seasoning' that are for sale.

A rebuilt field coil is not cheap, but it is cheaper to do it once and not have to tear everything apart again.
 
It could be shorted at one of many places around the coil ring. Unless it was shorted to ground at the magneto post connection it would likely produce SOME voltage despite being shorted.

Try the in car recharge, either it will work or not.

I always recommend doing a recharge before assembling the engine so you don't have this issue after it is all together. You can do a magnet recharge with the coil ring laying on top of the fully assembled magnets / flywheel before assembling the transmission to the engine. It's too late now but maybe someone will read this and not do the same thing that you have done.

oldmotorsguy said:
Red: I did indeed use new screws, but did not disassemble the transmission when setting the gap. I carefully removed the magnets when replacing the ring gear and put them back the way they were. Of course, who knows if they were NN SS when I got it. Wouldn't zapping it with 50 amps change it to the correct polarity in any event? But its possible that the magnets are not correctly installed. How are they supposed to be installed, and how can I tell if they are or not? With a compass? I will probably want to know this if I have to yank the transmission back off and start over.

I've used this epoxy quite a few times before on the coils, and it has yet to come off from my observations. You would think the unravelling of the existing tattered insulation areas if left alone would be more of an oil line clogging threat than sealing them with epoxy.

Coil ring: since I get a 2 volt reading currently at idle, the coil ring is not shorted out. If it were shorted out anywhere, I would get 0.0 volt reading (dead mag), or am I wrong about that?
Click to expand...
 
Red: I am measuring the voltage with an analog device that is perhaps 60 or 70 years old that I borrowed from a retired Motorola electrical engineer. He knows electricity like nobody else, but is not up to speed on Ford magnetos, but he said this unit would not lie to me.

In any event, I am jerking the ****** off the block today, going to shim to as close to .025 as I can get, and ensure my coil ring is rock solid. Additionally, I am going to make sure my magnets are all up to snuff and polarized correctly, although I am not exactly sure how that is going to go. But in the end, this is the absolute last time I am going to tear this apart, I am certain about that.
 
Farmall: I may take you up on your offer, depending on how things look when I tear out the transmission (again). I will have the magnets and field coil on my bench today, and will see what I have.

How much for a field coil ring, out the door, guaranteed up to snuff? I have perhaps four used rings laying around, none of them are perfect, and how would I check them out?
 
Royce: do you mind walking me through recharging the magneto on my bench before I put it back together? I intend on ensuring that all the parts involved are good before I proceed, and would love to know that I am good to go before putting the unit back together and then crossing my fingers at the initial run up.

FYI: I do the run up on an engine stand, not in the car. Too much pain and effort yanking the engine back out of the car if things go wrong.
 
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