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Allis Chalmers Discussion Forum
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Allis C mag

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Buddy Terry

09-06-2018 10:48:26




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Need some help and information on a FMJ Mag. Points not firing in mag. have installed new points, new condenser. I can ground a screw driver from a screw and hold it away from brass tab on mag and it fires, but will not fire to the points. Have checked wires coming from mag, they look ok, I know the mag is firing, I let my fingers get too close yesterday. I have done just about everything I can to get it to fire. Should the mag jump fire to the mounting plate that adjustment plate is ON? The mag model is 78124. Any information on this would be greatly appreciated. Thanks

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tractorguy2

09-06-2018 21:17:42




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 Re: Allis C mag in reply to Buddy Terry, 09-06-2018 10:48:26  
You shouldn't have spark at the points. If you do it means the points are dirty or you have a bad condenser.



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Dick L

09-07-2018 05:32:52




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 Re: Allis C mag in reply to tractorguy2, 09-06-2018 21:17:42  
I have worked on a bunch of magnetos and the first thing I check after opening them up is to see if I have spark at the points. If the condenser is shorted out you get no spark. If the condenser is open you still get spark and you will see the results on the points in burning. When points have power to them and closed the power is shorted out at that moment. Anytime you have power going to ground you will get a spark. Different power source but the same as shorting out an extension cord. Your going to have a spark.

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teddy52food

09-07-2018 19:33:01




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 Re: Allis C mag in reply to Dick L, 09-07-2018 05:32:52  
The spark you are seeing comes from the back EMF of the coil. If the condenser matches the coil perfectly, there will be no spark.



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tractorguy2

09-07-2018 19:25:10




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 Re: Allis C mag in reply to Dick L, 09-07-2018 05:32:52  
I've been working on tractors for decades. You should not have spark at the points.



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Dick L

09-08-2018 07:49:42




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 Re: Allis C mag in reply to tractorguy2, 09-07-2018 19:25:10  
Lets assume I am wrong and you are correct. I just need to know how that would work to not have a spark at the points. One side of the points are charged with electricity whether it be from a battery or from an electricity generator as part of a magneto. The other side of the points are grounded to the system. When you have power AC or DC grounded and you release that ground and there is no spark? When I take a wire on a AAA battery, which would be much lower voltage, and touch the wire to both ends at the same time I get a spark but it does not happen on ignition points. An 80 year old just needs some help on this.

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teddy52food

09-08-2018 10:35:07




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 Re: Allis C mag in reply to Dick L, 09-08-2018 07:49:42  
It is the job of the condenser to prevent sparking and points burning among other things.



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Dick L

09-08-2018 11:49:31




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 Re: Allis C mag in reply to teddy52food, 09-08-2018 10:35:07  
I was taught to set the timing on a distributor in the 1950's by having the power on and watching the points spark at TDC to see the exact time the points open. Built and raced a stock car in the 1960's and always set the timing watching the spark at the points and one night inbetween the heat race and the main I changed the distributor in the dark and set the timing watching the points spark. The Farmall C's coil went out this spring and the first thing I checked was the power in at the coil and watched to see if I had spark at the points when I had none I bought a new coil. After I installed the new coil the first thing I checked was to see if I had spark at the points with the power on. When I see the spark I put the rotor and cap back on and it started. Last fall when the Allis C with a magneto did not run and I had no spark at the plugs I put the magneto in the vice and took the covers off and watched for spark at the points when I snapped the drive over. When I didn't have any I put in a new coil and check for spark at the points. When I saw spark at the points snapping the drive over I put the cover and cap back on and when I put it back on the tractor it started. Since the 1950's I have been able to see spark at the points when the coil is good and I have power to the points. The only time I can't see spark at the points with the power on, the coil good and the point gap is correct is when the distributor cap is back on. The condenser coil does reduce shock of the spark to keep from burning the points. There still is spark if it is not shorted out somewhere.

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Lumbersawyer

09-06-2018 19:44:29




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 Re: Allis C mag in reply to Buddy Terry, 09-06-2018 10:48:26  
I just rebuilt my F4 mag for my 10-20 McCormick Deering. I never worked much with them other than cleaning the points, rotor and cap. I looked up several u-tube videos and various articles on how a magneto functions. I learned quite a bit about how they are suppose to work :) one article said the points should not spark much, if it does they won't last. The points run on the primary coil, low voltage. When they open, the primary coil then sends the electrical charge to the secondary coil where it is 200 times more powerful than the primary coil. The condenser absorbes the voltage to protect the points. I may not be completely correct with my explanation. I'm satisfied that my mag will fire with just turning it with my fingers. My impulse is still off so I could turn it more easily. As I understand it the points should not spark much at all. If they do your condenser might need replaced. I replaced both E15 ball bearings, coil, cap, and wires, bead blasted the housing and cleaned and painted every part. I have a new condenser but kept the original as it is still good. I thought about recharging the magnet but I don't think I need to with the good blue arcs I get now. It will jump a 1/4" gap very nice. I know the F4 is not the original for the 10-20 but it's what was on it when my Dad bought it back in the early 80's. I have a E4 lined up to purchase for my 10-20 when my friend and I can get together.

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Lumbersawyer

09-06-2018 19:40:38




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 Re: Allis C mag in reply to Buddy Terry, 09-06-2018 10:48:26  
I just rebuilt my F4 mag for my 10-20 McCormick Deering. I never worked much with them other than cleaning the points, rotor and cap. I looked up several u-tube videos and various articles on how a magneto functions. I learned quite a bit about how they are suppose to work :) one article said the points should not spark much, if it does they won't last. The points run on the primary coil, low voltage. When they open, the primary coil then sends the electrical charge to the secondary coil where it is 200 times more powerful than the primary coil. The condenser absorbes the voltage to protect the points. I may not be completely correct with my explanation. I'm satisfied that my mag will fire with just turning it with my fingers. My impulse is still off so I could turn it more easily. As I understand it the points should not spark much at all. If they do your condenser might need replaced. I replaced both E15 ball bearings, coil, cap, and wires, bead blasted the housing and cleaned and painted every part. I have a new condenser but kept the original as it is still good. I thought about recharging the magnet but I don't think I need to with the good blue arcs I get now. It will jump a 1/4" gap very nice. I know the F4 is not the original for the 10-20 but it's what was on it when my Dad bought it back in the early 80's. I have a E4 lined up to purchase for my 10-20 when my friend and I can get together.

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Buddy Terry

09-06-2018 18:13:40




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 Re: Allis C mag in reply to Buddy Terry, 09-06-2018 10:48:26  
Thanks, Steve, Dick and Teddy on the information. I will double check the small gears inside the mag cap. Even though I had a spark at the mag, I sill could not see it at the points. Have tractor sitting under lean--too, so it isn't in the sun, have even hung my cap over the mag to see if the points fired, could not see it, But I will check again. Thanks again to all of you.



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steve(ill)

09-06-2018 16:20:05




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 Re: Allis C mag in reply to Buddy Terry, 09-06-2018 10:48:26  
ted has a point.. If you took the front cover off and you can see two gears.. are they installed and TIMED right ? You need to have that correct to get the fire at right time.



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Dick L

09-06-2018 14:24:15




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 Re: Allis C mag in reply to Buddy Terry, 09-06-2018 10:48:26  
You should be able to see a spark at the points when the snaps magneto and spins the armature. At the same time the spark is seen when the points open you would get spark off the coil. If there is no spark at the points you would not get the magnified spark off the coil. If you was able to get spark off the coil you had to have spark at the points. You also would not get a shock off the outside of the magneto if you did not have spark at the points. On the magneto the spark at the points is less bright that from a distributor. I have a light over the vice I hold mangetos in to check them out and when I first check for spark at the points I turn the light off.

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teddy52food

09-06-2018 12:14:09




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 Re: Allis C mag in reply to Buddy Terry, 09-06-2018 10:48:26  
Why would you need fire at the points? The coil fires when the points break. Is the rotor timed right to get fire to the wires?



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