Farm Equipment - 1939 B Magneto no Spark

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1939 B Magneto no Spark

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=164879
Printed Date: 11 Aug 2025 at 12:08pm
Software Version: Web Wiz Forums 11.10 - http://www.webwizforums.com

Topic: 1939 B Magneto no Spark

Posted By: veeracer
Subject: 1939 B Magneto no Spark
Date Posted: 07 Oct 2019 at 8:24pm

I recently re-acquired a 1939 B that I owned 20 years ago. The owner said it ran and of course when I went to pick it up it didn't but I had faith that it would run again. So I brought it home, cleaned out the fuel system, put some new gas in it, and replaced the spark plugs. I couldn't get it started with the crank so I towed it with the truck for about 50 feet and it fired right up and ran great - for about 3 minutes.

When it quit running it was like someone shut it off (Killed the ignition), not like it ran out of gas. I took the plugs out of the motor so I could easily roll the motor over with the crank and now have no spark. It is a Fairbanks Magneto. I removed the upper housing on the magneto and when I roll the motor over I can see a faint spark at the points about every 2nd or 3rd "clack" of the magneto. Not the normal, consistent spark I have seen before when everything is operating properly. Any ideas what is wrong? Thanks for all the help.

Replies:

Posted By: MACK
Date Posted: 07 Oct 2019 at 9:03pm

File the points. Just bought a TL10. No spark. Filed points, good fire. MACK

Posted By: Gerald J.
Date Posted: 07 Oct 2019 at 9:32pm

I have a manual for a Fairbanks Morse magneto: Might not be the same model though.

http://geraldj.networkiowa.com/Trees/FM-Xmagneto.pdf" rel="nofollow - http://geraldj.networkiowa.com/Trees/FM-Xmagneto.pdf

Gerald J.

Posted By: Bill Long
Date Posted: 07 Oct 2019 at 9:40pm

If you have an ignition problem with a magneto you do the usual and replace points, condenser, rotor, and cap. Beyond that you would have to replace the coil. That usually solved all our problems. You can get parts from SteveNJ and if wanted he can overhaul the mag for you.

He is our in house electrical expert and a sponsor of this site

Take good care of my favorite. Sounds like the B was lucky to have you find it.

Good Luck!

Bill Long