Need help with a half working Fairbanks Morse Magneto

blue_tractor_man · Oct 25, 2018

Not exactly tractor related, but I have just aquired (not running, but "running when parked") Kohler 6.5 KW generator, circa 1965, with an L600 engine and a Fairbanks Morse X4B44B magneto. It is a 4 cylinder engine, so this magneto has a rotor and distributor cap. I get no spark out to the terminals where the spark plug wires connect, but if I take the cap off the mag and hook a jumper wire up to the little flat spring metal tab the thing puts out blue sparks. I have checked the continuity of the rotor, the little spring center pin and the cap. All check good. Is it possible that after 60 years something is weak and will not jump the rotor gap?

Janicholson · Oct 25, 2018

The rotor can have a carbon tract through the middle to the shaft. THe cap can have a carbon track or crack to the case. The button can be too short and not touch the rotor. Check these. Jim

moresmoke · Oct 25, 2018

Also, the rotor needs to be timed to the mag. Not sure how that one is, some have the rotor reduction gears after the points. The rotor/distributor contacts need to be in the right position when the mag sparks.

jeffcat · Oct 25, 2018

Just be very careful because magnetos are full of magic. They also can really bite you. Several have told you stuff to look for so be careful and patient. Double check your timing because that rotor must point to number 1 just as the impulse goes SPAP! Bet ya the wires got mixed around. Did you look to see if the plugs are full of crap and shorted out??

Dick L · Oct 25, 2018

It sounds like you have proven it is a hot magneto. When you put the cover over the points with the drive against the stop pin the rotor will not yet be pointing to the terminal. The small drive gear will have a tapered tooth on the OD of the gear. If you have a marked large gear you have only two choices. One is for clock ways and the other is for counter clock ways. With the tapered gear pointed down some of the magnetos have lug the rotor would point at to be set up for number one wire terminal. It would be slightly to the left to the terminal on clock ways.

blue_tractor_man · Oct 25, 2018

Thanks for the replies. I know the mag sparks because I used a jumper wire with alligator clips and a spark plug to test for spark. I will check timing, but I have no reason to think anyone has messed with the timing. I know the impulse works because at slow crank it goes "pop, pop, pop" and at fast crank it is quiet.

jeffcat · Oct 25, 2018

You are correct. That impulse MUST work. Keep going.

Steve@Advance · Oct 25, 2018

How much spark do you get with the jumper wire?

It needs at least a 1/4" spark.

I agree with Jim, a cracked/carbon tracked cap or rotor.

Put the rotor on, hold the jumper (with something well insulated) near the center of the rotor and crank it through. The rotor should not draw a spark. If it does, it is grounding through the shaft.

Look the underside of the cap over closely for carbon tracking.

blue_tractor_man · Oct 25, 2018

I was using a spark plug to check the spark, so maybe .035.

Waterloo · Oct 25, 2018

Moresmoke is correct. The rotor must be timed inside the cap. There are several websites describing the procedure. Fairbanks Magnetos were used on Lincoln welders look for Lincoln 250 SA.

Russ from MN · Oct 25, 2018

Spray the inside of the cap with water displacer, (WD-40) and then wipe out the excess.

dr sportster · Oct 26, 2018

It is nice to keep a new spare mag coil around for substitution when troubleshooting.

Need help with a half working Fairbanks Morse Magneto

blue_tractor_man

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Janicholson

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moresmoke

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jeffcat

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Dick L

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