MTFCA Forum

I'm trying to figure out why my car won't run on mag.
Was out last night running on mag, and the car suddenly stumbled and quit. I was able to catch it on battery and make it home fine.
Test bulb shows a weak light that barely increases in brightness as I increase rpm.
When I switch to mag the light almost goes out and it dies.
Test meter showing upwards of 20 volts at idle, but no increase with rpm on the meter or bulb brightness.

My question... Do I have a mag ring that has a dead zone now? Was running fine then failed suddenly.
Thank you
-Dan

Most probable cause is a dirty mag post contact.

Yep I agree, remove mag plug from transmission cover and you may find some fuzzies on the post or the mag button. If the spring in the mag post feels weak, replace with a new mag post.

Ok
I'll pull the mag post, clean and inspect it.
The pic is of the 1rst screen magnet cleaning last week.
Maybe the little fuzzy's attacked my mag post too.... we'll see shortly.

These fuzzies are iron.(magnetic) The fuzzies on the mag post would be from the bands

That's a lot of metal. I'd want to know where that is coming from.

T’s are fairly simple. Check the simple things first which is usually a mag post not getting good contact, loose mag connection wire at the coil box or the ignition switch. Do a quick temporary cleaning of the ignition switch by turning the key back and forth several times before you start it again and then turn to mag after it’s started on battery. Give it a try.

The metallic fuzzies may be from the magnet hold down clamp running to close to the field coils.

So.... I pulled and cleaned the mag post. Nothing on it. Spring on post is nice and springy. Checked the wire on the coil box and the back of the switch. I've cycled the switch. No improvement. Car will die when I switch to mag.
I don't get it.... This thing was running perfectly then it just went to sh#@%t. My rebuilt engine runs perfectly. It's a dream to drive. Mag just ain't workin'.
Mag test light still glows, but goes almost out when I switch from battery to mag.

The car's on jackstands and covered up. I've had it.

Gotta say thanks for all your kind help. "Thanks!"

I had one with a rebuilt engine, first time out, it was running on mag and suddenly died. It ran on battery for about 10 years. Then I rewound 3 mag rings and decided to install one on that car. So I pulled out the engine and found laying in the crankcase the funnel off the inside oil line. Apparently it was bent in such a way that the magnet hit it and broke it off. It cut the winding on the coil and then fell into the bottom of the sump. I had installed a magneto oiler on that engine when it was rebuilt and it had supplied enough oil to keep from ruining the engine.
Norm

Was the magneto coil ring rewound when the engine was rebuilt? I had the coil ring rebuilt on one of my T’s and reinstalled it. Worked fine for a while and quit running on mag. Kept dieing when switched to mag. Ran fine on battery. I removed the magneto contact and hardly dirty and no lint. Still wouldn’t run on mag and took it off again and used a mirrow to check the leaded button on top of the mag ring and noticed it wasn’t centered on top of the hole of the transmission cover!! Somehow when it was rebuilt the contact button wasnt centered!! I wasn’t going to pull the engine again so I bent the contact spring over to one side and installed it. Runs fine on mag now. It was touching some but after bending the spring over made a better contact and runs good.

Anything is possible on Model T’s and you will figure out what the issue is and most of the time it’s something simple. Take some time away from it and try again another time.

Been there and done that more than once.

Mag ring is a hand me down not a rebuilt one.
I'd love to pull the motor and take a look inside.

Professor Fate wrote: ↑

Sat Jul 30, 2022 9:09 pm

Mag ring is a hand me down not a rebuilt one.
I'd love to pull the motor and take a look inside.

Thats uber riskey when you consider the labor in switching it out if it fails.
Even with the capability of performing all the necessary tests on a used unit, I do not risk it on my own motors, and wont consider a used ring on customer rebuilds.
One of the tests is with my 110v armature test probes. In this case I might consider this, it might find & burn away a metal sliver short, but would kill the magnets requiring an in car recharge. A DC arc welder magnet recharge alone could fix the coil. Its all a crap shoot, but what you got to lose?.

That’s a lot of metal on that transmission screen magnet. Drain the engine oil looking for metal. I would then remove the starter drive, starter, and the transmission inspection cover and screen. I would shine a bright shop light into the transmission as someone slowly turns over the engine with the hand crank. You are looking for the source of the metal and any thing else amiss in the transmission and the condition of the field coil. Your used field coil, old coil wrapping may have failed and some of that metal may have shorted out some of the coils. See if you can find where the metal is coming from, it could be from something like a loose magnet pole striking the field coil or a brass plated steel band lining rivet scratching a transmission drum. You may not find the problem but keep a eye on the oil and transmission screen for more metal if you choose to run you T on battery to keep driving it.

Double post, sorry.

My friend, who started me on T's, has very graciously offered to pull the motor with me and make "adjustments" as needed. I'm hoping that happens before labor day. The car will sit as it is, on jackstands, for the duration.

That’s great for your friend to help you!
If the engine is taken apart I would replace the older used coil ring anyway whether it checks “good” or not.
This is one item that need to be replaced with a renewed one. An old original radiator that doesn’t cool but “looks good “is one thing to replace fairly easy. BUT a mag ring is a totally different thing!

Good morning Professor ... Doing the easy things first, I would replace the magneto contact with a new one, and then if necessary proceed to recharge the magneto.