Intermittent magneto

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Model T Ford Forum: Forum 2018: Intermittent magneto
Top of pagePrevious messageNext messageBottom of page Link to this message  By John Gelfer, Milwaukee WI on Wednesday, July 04, 2018 - 09:36 pm:

Just fired my engine after installing a new mag coil, and some transmission parts. It runs fine on battery, but stumbles on magneto. Tried substituting known good coils, but it didn't change anything. It's not a constant miss, just runs rougher with an occasional miss fire. BTW, it has an Anderson style timer. I'm hoping it's the coil box rather than the mag ring. Any ideas?


Top of pagePrevious messageNext messageBottom of page Link to this message  By John Doolittle on Wednesday, July 04, 2018 - 11:28 pm:

Sounds like a switch problem to me. Here's how to check. While the car is running on mag connect a jumper with an alligator clip on each end, one end connects to the coil box, the other end connects to the mag post. You have just bypassed the switch. Drive the car and see if the problem goes away.

A WORD OF WARNING- DO NOT operate the key switch while the jumper is connected. IF you accidentally turn to BATT with the jumper connected you will introduce DC current to the magneto, which can neutralize the magnets.


Top of pagePrevious messageNext messageBottom of page Link to this message  By John F. Regan on Thursday, July 05, 2018 - 11:13 am:

John:

Run the car on battery and test the magneto with an 1156 bulb and an ANALOG AC Voltmeter. Do this before you start swapping things or you may make it harder than it needs to be. Did you gap the magneto ring properly with a gapping setup gauge tool? Recharge the magnets when you swapped the mag ring? Having a uniform and correct gap is really necessary or the magneto won't put out enough current to make the motor run. Likewise the magnets would normally be recharged at this same time while the engine is apart. Does anybody in your chapter have a St. Louis Magneto tester? That would tell you instantly whether your magneto is OK or not.


Top of pagePrevious messageNext messageBottom of page Link to this message  By John Gelfer, Milwaukee WI on Thursday, July 05, 2018 - 08:42 pm:

Yes to all of the above, John Regan. We did have a gap gauge and recharged the magnets. Mike Zahorik is bringing over his magneto tester tomorrow, so we should know soon.


Top of pagePrevious messageNext messageBottom of page Link to this message  By John Gelfer, Milwaukee WI on Friday, July 06, 2018 - 09:35 pm:

St. Louis Magneto tester says the mag is 100% and the needle is steady. This is while running on battery though. As soon as you switch to magneto, the meter falls off by about 1/3, and the motor stumbles. Even though the tester has a built in load, it must be less than energizing the coils. Rewired and soldered all coil box connections with no change. Latest theory is the timer. It's a used Anderson. The constant 6V may make a worn timer a bit forgiving, but if the mag pulse hits at a time when there is poor contact it might be the problem? Will try a new timer and hope for the best.


Top of pagePrevious messageNext messageBottom of page Link to this message  By John Gelfer, Milwaukee WI on Thursday, July 12, 2018 - 01:05 pm:

Time for the happy dance! Ron Patterson suggested to Mike Zahorik that he thought it was a timer issue. It was. Tried a New Day timer and the brush was too long and scraped the inside of the timer cover so bad, it dragged it to full retard unless held hard. Anderson Timer brush we think was long enough to short inside the case. Just put in a TW carbon brush timer and it runs flawlessly on magneto.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Bert van Amstel on Friday, July 13, 2018 - 05:33 am:

Read your topic
I have also a smaLL problem with running on magneto, runs well but sometimes missing a fire
where is the Timer located?, so I can check also
regards
Bert van Amstel (Holland)


Top of pagePrevious messageNext messageBottom of page Link to this message  By Peter Claverie, Memphis TN on Friday, July 13, 2018 - 08:53 am:

Bert, the "timer" is located on the front of the engine, lower right side, back-to-back with the generator. It's the dome-shaped thing with wires attached. It rotates a bit when you move the "spark" lever (the one on the left of the steering column) up and down. The dome is held in place by a flat spring, under a bolt that holds the generator. Loosen the bolt a bit, so you can swing the flat spring out of the way, and remove the cotter pin through the end of the rod from the steering column. Then the timer can come off in your hand. It will still be hanging by its wires. Clean it out, including the rotating part that contacts the inside of it. It's likely that will fix your problem, but if not we can give further help. Just tell us what you saw and did, so we'll know where to start.


Top of pagePrevious messageNext messageBottom of page Link to this message  By John Doolittle on Friday, July 13, 2018 - 08:59 am:

Follow this link. The dome shaped device with the red wire attached is the timer.

There are several variations, so yours may look different.

http://www.mtfca.com/discus/messages/331880/355102.html?1381246141


Top of pagePrevious messageNext messageBottom of page Link to this message  By Bert van Amstel on Saturday, July 14, 2018 - 03:38 am:

Peter,
thanks today I will check this, now I understand what is ment with the timer.
Point is that my T runs well on battery and miss some fire on magneto, both systems walk over the timer as far i can understand.
Why the magneto course problems by timer and the battery doesn't I am interesting to understand the theory
Regards Bert


Top of pagePrevious messageNext messageBottom of page Link to this message  By Norman T. Kling on Saturday, July 14, 2018 - 11:34 am:

When you run on battery, the spark will come whenever the rotor is in contact with one of the segments in the timer. That is any place on the segment. When you run on magneto, your spark will come when the current reaches 1.3 amps. This could happen at any place on the segment. If the connection is poor at the point where the current reaches the point, you might not get a spark. This spot could vary according to the position of your spark lever. Another potential cause of the problem could be one or more coil not set to fire at 1.3 amps. Maybe the current does not build up enough for that coil to fire. A third cause would be a bad switch, but when the switch is inoperative, none of the coils would fire.
Norm


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