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Fairbanks Magneto operation
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Mike Whitman

09-12-2001 06:02:21




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I'm trying to figure out why I can't seem to get a spark from the right hand plug on my 1939 Model "B" (hand start) equipped with a Fairbanks Morse (not sure of model yet) magneto.My question is: When the impulse trips for the right hand cylinder(lower terminal on the mag cap), should I get a spark or does it only spark when the impulse trips for the left hand cylinder (upper terminal on the mag cap) ?
Here's wat I checked:
1. Gapped plugs (Autolite 3077) to .030
2. Nice blue spark on left cylinder's plug
3. Swapped plugs to be sure wasn't bad plug
4. Checked plug wire for continuity =ok&copper
5. Cleaned cap and rotor terminals(carbon?)
6. Measured resistance between inside cap terminal and outside terminal (where plug wire connects) and compared to left cylinder - left=20 ohms right=sometimes open/sometimes approx 250ohms/ sometimes 20 ohms - I'm thinking either this is the problem or that a Fairbanks doesn't spark on the right side when it's impulse trips - There is a spring that holds in the carbon terminal - I wonder if corrosion is preventing this spring from making contact with the piece that connects to the outside terminal.

I'm looking for ideas on what to check next.

Thank you very much for any help, my wife will be very glad when we figure out what's wrong with her tractor,
Mike Whitman

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Spokerd1

09-13-2001 20:14:26




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 Re: Fairbanks Magneto operation - question in reply to Mike Whitman, 09-12-2001 06:02:21  
Is this the mag that has been on the tractor and run before? Has anyone rebuilt it lately? Has the mag been taken off the tractor recently? Several things to check. Did the correct rotor get put in the mag. Is the top #1 terminal firing the left cyl. Maybe the mag is firing but 180 out. Check the sweep of the rotor to see if when the right cyl. is at TDC the the rotor is about to sweep past the lower terminal. I hope this might help some.

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Mike Whitman

09-14-2001 06:10:02




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 Re: Re: Fairbanks Magneto operation - question in reply to Spokerd1, 09-13-2001 20:14:26  
This is the magneto that was on the tractor when I bought it. It ran pretty decently when I got it but just started missing on the right cylinder. I got the model number using the paper rubbing method (J4B3). Turns out this may be a mag that was destined to be on an Alis Chalmers (4 cylinder?) and someone placed a 2 cylinder cap on it. I can live with the impulse only providing a spark to the left cylinder for now but it isn't providing a good sspark to the right cylinder when running. I'm new to this so I'm not sure what the characteristics of the spark should be. I placed new plug wires with snap-on terminals so that I could pull them off and hold them away from the spark plug (while running)to determine what the spark looked like. I observed that the left hand side can produce a blue spark about 1/2 inch long. The right side can only produce an erratic spark about a 1/16th to 1/8th. Another thing I saw, but didn't expect, is that the spark on both sides "seemed" continuous. Should it appear this way or should I see on/off ?

Thanks for any trouble shooting tips on magnetos,
Mike

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Spokerd1

09-16-2001 06:07:59




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 Re: Re: Re: Fairbanks Magneto operation - question in reply to Mike Whitman, 09-14-2001 06:10:02  
Mike from what I am hearing is that one side is stronger on spark than the other. And it seems you have continous spark on one side. That can be caused by the rotor or the cap. Carbon tracking. I think that I would look around and fine a good Wico mag, and replace the mag. As you say it is not the correct mag. You might want to call 1-800-522-7448 and order a couple of books to help you out. SM-2029 and you might want to buy the SM-2000 from Deere. The SM=2029 will give you the correct mag that should go on your Deere. I hope this helps

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