Need some magneto 101
Printed From: Unofficial Allis
Category: Allis Chalmers
Forum Name: Farm Equipment
Forum Description: everything about Allis-Chalmers farm equipment
URL: https://www.allischalmers.com/forum/forum_posts.asp?TID=137930
Printed Date: 23 Oct 2025 at 7:51pm
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Topic: Need some magneto 101
Posted By: bobkyllo
Subject: Need some magneto 101
Date Posted: 30 Apr 2017 at 9:22am
So I bought an allis wd for a song. Guy said he had it running this summer. I met this guy through a customer and the customer gave very good feedback of the owner. So I have to believe that it did truly run this last summer.
I got it home yesterday and I can't get it to start. I pulled the tractor with about tractor. I can't get even a sputter from it. I'd like to look in the mag but I'm not sure how to go about that. It looks like two caps on it. One small one where the wires hook on and a much bigger ones behind that.
What am I getting into there. I know there is a rotor I'd like to look at and see if it's corroded.
When I pulled it you could here the impulse clicking. I tried pulling it faster and slower with no luck
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Replies:
Posted By: Steve in NJ
Date Posted: 30 Apr 2017 at 9:53am
Sounds like its equipped with a "J" or "X" series Mag with upper cap, lower cover. If you just want to inspect the rotor, remove the two 8-32 screws from the end cap (where the wires attach) and you'll be able to inspect the rotor. My assumption is that if it was running last summer and not now, the points probably have a film of oxidation over them and the points need a little spritz of TV tuner cleaner or Brakekleen to rid the oxidation killing the spark. Don't use a file. Just a spritz should do the job.
Now, when you remove the lower cover, you'll be taking the Mag out of time. How to put the Mag back in time is there is a "C" and and "A" stamped into the fiber timing gear. On the main shaft steel gear, (depending on which Mag you have) there will be either a "dog ear" on one of the steel gear's teeth, or a "Pip" (dimple) mark on the tooth that needs to line up with the fiber gears "C". (do not use the "A") Once both are aligned, the Mag is now back in time. Depending on the Mag lower cover's condition, there usually is a decal inside the lower cover telling you how to align the marks. In a lot of cases, that decal is either gone or mostly worn off from age. Some are lucky to still have the decal, but as long as you know how to time it as I explained, you should be good to go. Also sounds like the impulse is working, so you should be good there.... HTH
Steve@B&B
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39'RC, 43'WC, 48'B, 49'G, 50'WF, 65 Big 10, 67'B-110, 75'716H, 2-620's, & a Motorhead wife
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Posted By: bobkyllo
Date Posted: 30 Apr 2017 at 11:46am
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Thank you Steve. Can I get to the points with out removing the lower cover. If memory serves I think the mag says fmj on it. So I'm guessing it's a Fairbanks Morris model j.
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Posted By: DanD
Date Posted: 30 Apr 2017 at 3:50pm
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Not to insult your intelligence but have you determined that there is no spark? Did you pull the plugs and check? Were the plugs wet or dry? Do the basic workup before starting exploratory surgery!
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Posted By: bobkyllo
Date Posted: 30 Apr 2017 at 5:35pm
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Plugs are not really very wet. They are a bit. I think my spark is well because every now and then I get a small pop. But that's far and few between
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Posted By: DanD
Date Posted: 30 Apr 2017 at 6:06pm
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My point was just to make sure you actually have no spark before you start disassembling the magneto. Be sure to check out the carburetor. And if you have no spark at least try it with the magneto ground wire unhooked to eliminate a problem with the ground wire or switch. Again just try easy first. Doesn't usually work but always worth a try.
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Posted By: WC7610
Date Posted: 30 Apr 2017 at 6:39pm
while turning it over check each wire one by one holding them with a gap between wire and plug to see if they have a spark. Will confirm or eliminate one problem.
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Thanks
Most Bad Government has grown out of Too Much Government- Thomas Jefferson
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Posted By: Steve in NJ
Date Posted: 30 Apr 2017 at 10:32pm
Another thing that I forgot to mention in my first post, if the Tractor is equipped with a remote kill switch up near the driver, disconnect it and see if the spark magically appears again. If it does and it starts up, there's your culprit! Bad kill switch.
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39'RC, 43'WC, 48'B, 49'G, 50'WF, 65 Big 10, 67'B-110, 75'716H, 2-620's, & a Motorhead wife
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Posted By: Bill Long
Date Posted: 01 May 2017 at 8:57am
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Listen closely to what is said above. You are very fortunate to have been given outstanding information from some of our best electrical experts. Good Luck! Bill Long
ps: If you do have to get into the mag do not be intimminated. If I can do it I am certain you could. However, do the very basics first before getting into the mag.
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