Farm Equipment - Magneto Mystery

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Magneto Mystery

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=16512
Printed Date: 05 Feb 2025 at 5:58am
Software Version: Web Wiz Forums 11.10 - http://www.webwizforums.com

Topic: Magneto Mystery

Posted By: countryguy828
Subject: Magneto Mystery
Date Posted: 13 Aug 2010 at 11:04am

Put my B back together to mow with it last week. I got the back yard mowed, then it quit running. I had a friend drag me around till it started again. Except it would only run on cylinder #4, we took the cap off the mag and cleaned everything put it back together and it would only run on #3.

We took the plug wires off that weren't firing and put a screwdriver in the cap in those locations and went to ground with no spark from them.

We have it narrowed down to the mag for sure, but can't figure why 1 cylinder runs nice n strong while the other 3 won't do anything.

Dave

Replies:

Posted By: Gerald J.
Date Posted: 13 Aug 2010 at 12:29pm

Broken rotor or gear in the distributor section.

Gerald J.

Posted By: countryguy828
Date Posted: 15 Aug 2010 at 7:49pm

Gerald got it nailed down pretty close...

I took the cover off the mag and was able to turn the rotor easily by finger. Pulled that cover off and the gear looks to be in decent shape. Is it possible the cap just shifted upwards a tad bit and the teeth UN-meshed? I had the cap off to paint and retime. The mag had been out by 90 degrees anyways, #1 was were #3 should have been etc.

Next problem, went to grab trusty crank to turn motor over...missing, drove 20 miles to the showgrounds where I last used it, not to be found, must have fallen out while going down the highway or someone found it and borrowed it permantly.

Dave

Posted By: Gerald J.
Date Posted: 15 Aug 2010 at 8:22pm

Check the rest of the gears and the bearings. A worn bushing will let the gears slip without having worn the teeth all the way off the gears. I just wore out a drill that way.

Gerald J.

Posted By: Steve in NJ
Date Posted: 17 Aug 2010 at 7:58am

Sounds like a bad set of points where the spark is going to the breaker plate. Renew the points/condensor and give it a whirl. If there's been high humidity in your neck of the woods, that'll do it.

mailto:Steve@B&B - Steve@B&B

Posted By: countryguy828
Date Posted: 17 Aug 2010 at 9:06am

I put the everything back in time yesterday. I slid the cap downward as far as I could and tightened the screws. The rotor gear was engaged with the mag side gear. Took a few cranks(borrowed crank from Massey Pony) but started up like a champ. I was able to get it off the trailer. Don't know how long it will last, that gear will probably need replacing soon, but as cheap as I am, I will wait as long as I can.

Maybe someday I will buy a new battery and be done with this cranking business. Already had the starter rebuilt once...

Dave

Posted By: Dick L
Date Posted: 17 Aug 2010 at 9:13am

I would tend to lean toward the points as well. Might want to check the gap. Points that have the lifter on the cam broken and just making contact will act like that. I have reset points that have had that happen in the field and run until I could find time to put in new ones. matter fact my Farmall C needs new points that I had reset last year when the plastic lifter broke and have not replaced them yet. Kinda gotta thank yall for bringing back to mind.

Posted By: countryguy828
Date Posted: 17 Aug 2010 at 9:20am

The mag side is fine, the rotor wasn't turning.

Posted By: Dick L
Date Posted: 17 Aug 2010 at 10:54am

Good Deal, Glad you got it figured out.