MAGNETO TROUBLESHOOTING

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John Dow
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MAGNETO TROUBLESHOOTING

Post by John Dow » Sat Nov 09, 2019 3:27 pm

Hello Everyone. I'm having trouble with the magneto "cutting out" on my '23 Touring. I'll be driving along normally when it quits. The wiring and connections are good, I have replaced the back of the switch and the magneto post. There's nothing left but the magneto itself, right? Can anyone tell me what the resistance reading should be from the mag post to ground? I suppose I need to figure out if the circuit is opening up or grounding out. Many thanks.


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Re: MAGNETO TROUBLESHOOTING

Post by John kuehn » Sat Nov 09, 2019 3:53 pm

Sounds like it has an intermittent connection cutting out. You say it runs fine on mag but then just cuts out. Start the car and switch to mag. Star jiggling the connections.
Have you removed the mag post and cleaned off any lint or etc?
Also check to see if the mag post spring is making a good contact to the button on the mag ring.


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Re: MAGNETO TROUBLESHOOTING

Post by John Dow » Sat Nov 09, 2019 4:05 pm

Thanks John. I've done all you suggest including replacing the mag post.


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Re: MAGNETO TROUBLESHOOTING

Post by Dallas Landers » Sat Nov 09, 2019 4:12 pm

Have you checked the switch? Had that trouble with my TT. Bad contact in the switch was the problem. Just a thought.


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Re: MAGNETO TROUBLESHOOTING

Post by Dallas Landers » Sat Nov 09, 2019 4:14 pm

I should read more careful. Switch has been repaced.


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Re: MAGNETO TROUBLESHOOTING

Post by John kuehn » Sat Nov 09, 2019 4:32 pm

If you have checked the connections as mentioned above maybe it’s a bad solder joint somewhere on the mag ring. But before you pull the engine to remove and check the mag ring I would double check all the outside connections first. Is the original mag ring in the car and not a rebuilt? Maybe others might know but if the magnets were getting weak it seems like it would get to where it wouldn’t run at all.


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Re: MAGNETO TROUBLESHOOTING

Post by Ron Patterson » Sat Nov 09, 2019 5:11 pm

Have you checked the crankshaft end play?
The magneto output is reduced by the square of the distance the gap increases.


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Re: MAGNETO TROUBLESHOOTING

Post by John Dow » Sat Nov 09, 2019 5:32 pm

Thanks everybody. I bought the car 5 years ago and it had had a "ground-up" restoration and total engine rebuild. It has run superbly until recently. With the engine rework I assume the mag coil ring had been replaced as well and I can see the contact point is shiny like new. When the magneto is working the engine runs with lots of power. I believe I either have an intermittent short or an open circuit. As I asked originally I'd like to know how many ohms I should get when I test from the mag post to ground.

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Re: MAGNETO TROUBLESHOOTING

Post by Bill Robinson » Sat Nov 09, 2019 6:00 pm

Will your car start on magneto? If so, make up a jumper with an alligator clip on each end.
  • Disconnect the FORD stock wire at the mag post.
  • Disconnect the FORD stock wire at the coil box.
  • Connect one end of the jumper to the mag post.
  • Connect the other end of the jumper to the coil box connection
  • Start the car- DO NOT activate the key switch
  • Drive the car to see if the mag cuts out. If yes- the problem is in either the coil box or the magneto. If no- the problem is either in the switch or wiring,
  • A WORD OF CAUTION- do not allow DC current to accidentally- de-magnetization of the magnets will occur.


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Re: MAGNETO TROUBLESHOOTING

Post by Scott_Conger » Sat Nov 09, 2019 6:42 pm

John

the mag ring is grounded to the block. When new, resistance is around .5 Ohm. If you have a short at one of the coils to ground, you're going to have a darn hard time determining that.

You are assuming a lot, when you state that you replaced the back of the switch, and are now ignoring it as a source for the circuit being intermittent.

Also, go back and re-read what Ron Patterson asked you.
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Re: MAGNETO TROUBLESHOOTING

Post by John Dow » Sat Nov 09, 2019 7:17 pm

Many thanks Scott. You may not remember but you helped me with my last mystery -- unexplained engine rattle. One of the things I checked while running the loops was cam shaft end play. It was found to be within limits. (BTW my problem was engine knock caused by my aluminum high compression head. My remedy has been running 91 octane and less advance. No more rattle!!) I may be dealing with Gremlins. Tonight I burning a corn cob so it can smolder under my car and passing my neighbor's black cat six times over the radiator.


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Re: MAGNETO TROUBLESHOOTING

Post by Scott_Conger » Sat Nov 09, 2019 9:21 pm

that ought'r do it!
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Re: MAGNETO TROUBLESHOOTING

Post by Norman Kling » Sat Nov 09, 2019 9:50 pm

On a 23 you Your switch should have a post on one side for battery and on the other side magneto. wire and connect the battery to that side of the switch. Tape up the magneto wire so it won't touch anything connected to the battery. Then run the engine on battery with the switch in the magneto position. If it still cuts out, your problem is in the switch, the wire, or the coil box. While you run on battery, you can also test the magneto output to see how much it produces. You need an analog AC volt meter. You should have at least 6 volts at idle and higher as the speed of the engine increases up to around 30 volts AC. Note, at high speeds the bulb might burn out. Test between the mag post and ground with the meter across a 6 volt light bulb. When a magneto gets weak, sometimes it will drop below 6 volts at idle or low speeds and will work OK at higher speeds. In that case the magneto either needs re-charging or you have too much end play in the crankshaft. The flywheel will move away from the coils when going up a steep hill or when you depress the clutch into neutral or low gear.
Norm


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Re: MAGNETO TROUBLESHOOTING

Post by John Dow » Sat Nov 09, 2019 10:26 pm

Question: If the engine runs fine on battery how can the problem be with the coil box if it won't run reliably on magneto?


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Re: MAGNETO TROUBLESHOOTING

Post by Scott_Conger » Sat Nov 09, 2019 10:36 pm

There is wiring, pinch points, and insulation resistance all to consider.

Your box may or may not have the 2nd post for the mag connection...I don't recall from your posts. Anyway, here is what goes on out of sight on this version of coil box wood.
PB020038.JPG
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Re: MAGNETO TROUBLESHOOTING

Post by Eck » Sat Nov 09, 2019 10:55 pm

I thought I had a mag problem and thought it ran fine on battery. While troubleshooting I noted #4 coil was firing so I turned the crank to move on to another coil. To my surprise moving the crank did not silence the coil and found #4 connection on the timer was grounded all the time. Changed timer and wire and problem solved. Maybe disconnect the mag post wire and connect a 1156 bulb to the post and ground and start and run on battery and watch the light for mag problems.


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Re: MAGNETO TROUBLESHOOTING

Post by John kuehn » Sun Nov 10, 2019 8:52 am

Don’t know if you’ve rebuilt the coil box but an intermittent can certainly occur because of an original coil box. Age catches up to coil boxes as with other original electrical components.
When restoring a T the coil box is the first thing to rebuild in the electrical system.


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Re: MAGNETO TROUBLESHOOTING

Post by John Dow » Sun Nov 10, 2019 10:12 am

Thank you John. Your suggestion is good but if the coil box is the problem wouldn't it not run when on battery as well?

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Re: MAGNETO TROUBLESHOOTING

Post by Steve Jelf » Sun Nov 10, 2019 11:09 am

...if the coil box is the problem wouldn't it not run when on battery as well?

Correct. On your 1923 the coil box has only one input. It takes current from both the battery and the magneto. That makes the switch a leading suspect. I would first determine whether there's normal output at the mag post. If there is, then the problem has to be somewhere in the path from the mag post to the coil box. That would be in the switch or one of the connections. A problem I once found there was a cracked terminal block that kept one of the screws from making a tight connection.
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Re: MAGNETO TROUBLESHOOTING

Post by jab35 » Sun Nov 10, 2019 1:34 pm

Wouldn't running on battery with magneto disconnected but loaded with an 1157, 12 volt automotive bulb and ac voltmeter determine if the mag 'cuts out' ? Perhaps the bulb alone would give indication, if it dims at higher rpm it would confirm Ron's diagnosis of excessive flywheel clearance. good luck and pls post final outcome, jb

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Re: MAGNETO TROUBLESHOOTING

Post by ewdysar » Sun Nov 10, 2019 1:45 pm

My father still tells the stories about driving his touring with magneto headlights in the 60’s. He says that the headlights would get momentarily brighter when he hit the brakes to slow down or stop. He knows that it was moving the crank forward and getting the magnets closer to the magneto. But the mag still had plenty of power for the coils, regardless of the crank position in the bearings. He was also still using a 6V dry cell lantern battery for starting. That battery was dead after 25 years of storage when I took possession of the car.

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Re: MAGNETO TROUBLESHOOTING

Post by Norman Kling » Sun Nov 10, 2019 3:35 pm

Steve brings to mind one other thing about the terminal block on the firewall. With a steel firewall, if you should have a screw a little too long, it could make contact with the firewall and ground out the circuit. It could be just on the cusp and the vibrations of the car could move it to make or break the contact. Not a likely candidate, but something to look at.
Norm


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Re: MAGNETO TROUBLESHOOTING

Post by John Dow » Sun Nov 10, 2019 6:42 pm

Thank you one and all for your interest in my problem and your extremely helpful suggestions. I'm sorry to report my problem is the magneto is simply not producing any voltage at all. I do not see any path from here other than a magneto coil assembly replacement at my next (if ever) engine rebuild. Thank you again for this and all the countless times you folks have helped me understand and work on my T.


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Re: MAGNETO TROUBLESHOOTING

Post by Scott_Conger » Sun Nov 10, 2019 6:54 pm

John

what was the test that you did that verified zero output on the mag?
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Re: MAGNETO TROUBLESHOOTING

Post by Scott_Conger » Sun Nov 10, 2019 6:56 pm

John

what was the test that you did that verified zero output on the mag?
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Re: MAGNETO TROUBLESHOOTING

Post by John Dow » Sun Nov 10, 2019 7:02 pm

Hi Scott, I disconnected the magneto lead and checked AC voltage from the post to ground. The needle on my multi meter read zero and didn't budge with changes in RPM.


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Re: MAGNETO TROUBLESHOOTING

Post by Scott_Conger » Sun Nov 10, 2019 7:11 pm

You might want to put a prybar between the front crank pully and block and see if with gentle persuasion, the crank will move forward a little bit. If there is detectable movement, there is some chance that voltage will be restored with magnets closer to the mag ring, and if this is true, there is a shim sold that can be custom fit to the front of the engine which will keep the crankshaft forward resulting in more output. There are other fixes, if this is the case, but it's not easy to fit a new bearing shell with proper clearance with the engine in the car though it can be done.

When you do the above, and have a dial indicator on the pulley, all the better.

I find it hard to believe that a 5 y/o rebuild will have a rear main that worn, but who knows how it was fitted

And finally, you used an analog voltmeter, right?
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Re: MAGNETO TROUBLESHOOTING

Post by Eck » Sun Nov 10, 2019 8:09 pm

On mine I used a digital meter and got a bad reading. use the 1156 bulb and it lit bright try the bulb before throwing in the towel. if putting out any , the bulb will light, cost very little.!!


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Re: MAGNETO TROUBLESHOOTING

Post by John Dow » Sun Nov 10, 2019 10:13 pm

Yes, I used an analog meter. The needle didn't budge.

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Re: MAGNETO TROUBLESHOOTING

Post by Fordwright » Sun Nov 10, 2019 11:24 pm

I was thinking the coil box may be out of adjustment, but since there are four of them, they would never cut out all at the same time, so that's not it.

I'm not sure what he means by "magneto cutting out," because on the '23 model it had a crude electrical system separate from the flywheel magneto. It was still possible to drive the ignition from the flywheel magneto, but it also had a storage battery, needed for the starter, which was charged by a generator, which would normally run the ignition coils. The generator cutout would have no bearing on the ignition cutting out, because it's purpose is primarily to prevent current from bleeding back through the generator, and the generator doesn't drive the ignition either, it mainly charges the battery..

If it hasn't been mentioned already, a possible point of failure is in the ignition timer, which some people also call a "distributor." If the main power lead to the timer is cutting out, it could cause all four ignition coils to stop working.

At least that's what I can suggest by the information provided so far as I understand it.

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Re: MAGNETO TROUBLESHOOTING

Post by Steve Jelf » Sun Nov 10, 2019 11:59 pm

If it hasn't been mentioned already, a possible point of failure is in the ignition timer, which some people also call a "distributor." If the main power lead to the timer is cutting out, it could cause all four ignition coils to stop working.

A timer and a distributor are two different critters. A timer has no main power lead going to it. It's a rotating switch that grounds each of the four wires from the coils in order. A distributor has a single main power lead from a single coil, and distributes high tension current from the coil to each of the spark plugs in order.

From what I've read so far, I assume this car has the Ford setup of a timer and four coils. The fact that it runs normally on battery says the timer is OK.
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Re: MAGNETO TROUBLESHOOTING

Post by Fordwright » Mon Nov 11, 2019 1:06 am

Steve Jelf wrote:
Sun Nov 10, 2019 11:59 pm
If it hasn't been mentioned already, a possible point of failure is in the ignition timer, which some people also call a "distributor." If the main power lead to the timer is cutting out, it could cause all four ignition coils to stop working.

A timer and a distributor are two different critters. A timer has no main power lead going to it. It's a rotating switch that grounds each of the four wires from the coils in order. A distributor has a single main power lead from a single coil, and distributes high tension current from the coil to each of the spark plugs in order.

From what I've read so far, I assume this car has the Ford setup of a timer and four coils. The fact that it runs normally on battery says the timer is OK.
Thanks for correcting me, but a faulty ground would cause the same problem.

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Re: MAGNETO TROUBLESHOOTING

Post by Mark Gregush » Mon Nov 11, 2019 1:22 am

The Model T ignition system for battery; The negative lead to frame for ground and the positive goes to the terminal block thru the switch to the base bottom strip contact of the coil box. When the roller, which is grounded, come in contact with one of the segments in the timer it closes that circuit and supplies power to one of the coils. That coil fires a plug which goes to ground completing the firing circuit. The magneto is the same only the power is supplied by it. The coils them self's are not grounded.
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Re: MAGNETO TROUBLESHOOTING

Post by Fordwright » Mon Nov 11, 2019 2:33 am

Originally, the flywheel magneto was only for a source of power for the ignition coils. It replaced dry cells on earlier Ford cars before the Model T, and dry cells were still used in some Model Ts to make starting easier, but they didn't last a long time and cost money to replace. In those days "magneto" had a slightly different meaning than we know it today. It was simply a crude AC generator, and did not provide ignition spark, but provided the current to drive the ignition trembler coils. Later, the magneto was also used to power electric lights when they replaced the gas-powered and kerosene lamps on the car.

Other manufacturers were offering something called "magneto ignition", which eventually shortened to what know as a "magneto" today. It was essentially a self-contained ignition system that had a built in magneto to supply power to its coil-driven points-and-condenser that later became the standard for many decades, generally up until the 80s, and in some applications today. But Henry Ford disliked ignition magnetos, mainly because his existing system worked just fine and the price of the ignition magnetos available to him would cost him $140 at that time, which was outrageous for a car that sold for less than a thousand.

When Henry Ford became convinced that an electric starter was essential because the crank was difficult or impossible to use for some, he started including them on his cars from 1919 onward. But he couldn't use his existing flywheel magneto for any part of the starter system, mainly because it produced AC not DC, and the volts ranged from zero to 30 volts. So another electrical system was installed, which consisted of an electric starter, powered by a storage battery and recharged by a generator. It was also a better way to run accessories like electric lights, because it was a more stable voltage, and it could also run the ignition trembler coils. But Henry didn't eliminate the flywheel magneto, even though that might have made sense to another automaker, but it did remain throughout the entire production run of the Model T.

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