Fairbanks Morse FM magneto for WC problems

Oliver662011 · Sep 9, 2013

I have a magneto off a WC I need some insight on how to repair the problems. First the impulse doesn't snap when you rotate it and the spring is in good condition and in properly I believe. Second someone sheared off the the alignment pin for the pinion gear, any ideas? I could really use some help. Thanks
Mike

stu (ON) · Sep 9, 2013

Go to Section 7 and see what you can figure out.

http://www.oldengine.org/members/diesel/FairbanksMag/MagFmBook.htm

red.green · Sep 9, 2013

You didn"t state which mag so I"m assuming its an FMJ4B3.

First did you take it apart? If so did you install the spring in the proper direction?

As for the drive pin, I just repaired one for a customer that had a sheared pin. I drilled out the pin through the hole in the end and then used a small punch and drove the remainder of the pin into the center then drilled the scrape out. The pin is fairly hard and probably moves around in the hole. It took several drilling with an increase in size until I was at full diameter.

This little drilling session probably took a couple hours, with allowing time for the metal to cool.

Oliver662011 · Sep 9, 2013

That is a great website, and yes I have taken it apart. I guess where I am confused is does the "clock" spring in the impulse get a preload or no? Also how do I know the proper direction of the spring is that dependent on the rotation of the engine? And additionally thanks for the reply on the pin, I am pretty sure I can handle fixing it, where do I get a new pin? Thanks Mike

red.green · Sep 9, 2013

If you didn’t remove the spring from the drive cup it should be in the cup in the proper direction.

Yes they have to be wound up to work. With the other end of the mag held in place with a vise grips or a wrench you have to wind the spring against the backing plate. It’s a process of pressing the cup against the backing plate and when the ears on the back of the cup hit you have to lift it of the backing and continue to wind until the ears drop down into the cutout after another half turn.

Depending on the strength of the spring it may be a half to one turn for a strong spring and maybe another turn or half for a weaker spring.
I will look tomorrow and see if I can find another pin lying around. I hope this helps

old · Sep 9, 2013

Send me an e-mail and which mag you have and I can in turn send you the manual for that mag. I have the 2 most common mag manual used on the A/C tractors in the computer

Fairbanks Morse FM magneto for WC problems

Oliver662011

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