car will not run on magneto

[Mike]

Hi to all,
I am working on a 1919 Model T and my question is when the car is running on battery the car runs well, when I switch it from batt to mag the car shuts off, The wiring is correct and is new 2 years old, I cleaned the mag pick up, and replaced the ignition switch.

Any suggustions would be helpful

Mike

[Doug Money]

Have you measured the mag output with a 1156 bulb and analog meter?

[Mike]

No I will do that now! and I will get back to you tonight

mike

[Mike]

Ok I am new to Model T ! Can you tell me how to test the mag with a 1156 bulb and a anolog meter

Mike

[Greg Jones]

Did it previously run on magneto and this is now a new condition, or has it been this way since you got the car?

[jkeesey]

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Come on Mike its just a ford! All kidding aside the ideal T mag puts out near 24 volts. Just hook your voltmeter to the mag output when running and see what shes got. If your running well on batt your coilpacks must be balanced fairly well.

[Doug Money]

Run car on battery and hook a 1156 bulb in line with an analog voltmeter to the mag post. Post your readings at idle and fast idle.

[Mike]

Greg,
Yes it ran very well on mag, I changed the rear and now i have the mag problem

Mike

[FRANK PKNY]

Need to check the voltage with a analog meter at the mag post. Hi idele about 24v AC . A digital meter will not give you a good reading. Then follow the circite from the mag post to the post that goes to the coils. A real good rebuilt mag will put out 30+ volts AC the coils like the ac voltage better than the DC from a battery. I don't know why but that is the way it is.

[Doug Money]

Frank, the higher voltage increases the ramp up time of the coils so they fire faster increasing timing. This makes the engine run a bit faster. The AC voltage helps keep the points from burning since the charge reverses from time to time through the points when the coil is charging.

[Greg Jones]

Yes you should test the mag output as recommended, but I am intrigued by the sudden change. When you say you changed the "rear" I assume you mean rear axle? Did you disconnect any wires, or that sort of thing? I can't imagine changing a rear end would cause this. Do you have any idea of the condition of crank endplay?

[Greg Jones]

Also, make SURE you really cleaned the magneto post, including down inside the hogshead under where the post screws in. I had a problem once with the car missing and finally dying while on magneto. I pulled the mag post and thought, aha!, here is some band lint causing the problem. Well that was only part of the problem, there was still a hunk of lint inside on the coil ring post. Only spotted that by looking in there with a flashlight and yanked it out with thin needle nose pliers. Worth a look, anyway....

[Mike]

Greg,
Yes I changed the rear end assembly, I did not check the end play of the crankshaft.
I did pull the mag out of the hogs head and really cleaned it up

[ljbohlen]

Do you have an outside Mag fed oil line?
Sometimes these can short the Mag.
Make sure the fitting for the line is not screwed in to tight as it will contact the mag post and kill the Mag.

Also check your switch. Some times weird things happen, you change out the rear end and for some unknown reason the switch decides to crap out the next time you start the car. Totally unrelated but it will have you chasing your tail for weeks or more....

T's are the most ornery machinery ever built.

Good Luck.
Larry

[Greg Jones]

Aha! So the magneto was out. I assume you mean the whole transmission with the magnets on the flywheel. Did you also remove the coil ring that bolts on the back of the block? If so did you notice any shims behind it? The gap between that coil ring and the magnet contacts on the flywheel needs to be 0.025 to 0.040" if I remember correctly. That is actually a pretty narrow range when you think about it. So my question: Were there any shims and did you replace them as you found them? Dont feel bad if you say you didnt put them back in-lots of people have done this. Not looking to make you foolish, just asking the questions to help you get to the bottom of your problem. Something changed physically since it was last running on mag, obviously. Now to figure out what....

[jkeesey]

I think he meant the mag pickup not the entire magnetto.

[Doug Money]

First step in trouble shooting is to see if there is in fact any voltage coming from mag as described above. Otherwise you are just grasping at straws on the fix.

[Greg Jones]

Of course, do the test. Was trying to slueth back to what has been changed since it was working. But do the test.

[Mike]

I did some tests this weekend, I am getting 3 volts at the mag pickup. I recharged the magnets and I still get only 3 volts.

Mike

[yachtsmanbill]

Three volts at what engine speed? ws