Fairbanks-Morse Magneto help

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pa340dart

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Location
Somewhere in NEPA
I inherited a Hi Power 2000W generator powered by a Wisconsin gas motor
It spins free but has a very low spark
Points, condenser changed
Has a Fairbanks Morse mag
Anyone familiar with this and knows the procedure on how to “excite” the mag’s
Coil with a a battery charger?
This thing sat for 20+ years
Would like to see if it will run without putting out $100 ++ to get a replacement magneto just to start it
Or should I trash it and buy a modern generator
Thanks

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"Generally" the problem with any mag type system is the points, condenser, or coil. In the case of "some" mags there are various rotating devices--such as for the rotor--that add complications

(In the one off our old Farmall Regular, the points actually rotated when it ran, very tough to troubleshoot that old girl}
Points MUST be in good shape and have very low resistance
Condenser MUST be good and have LOW leakage and you can not test that easily nor with a multimeter. A new condenser does not mean a 'good' condenser
So far as the coil, they can have "partially" shorted windings and still pass the ohmeter test and if they have ingressed moisture, you might be able to bake them at low temp for a few days then if they work re-seal them with appropriate sealer but this is a iffy situation.

If the cap/ rotor are dirty/ moist/ carbon tracked, they will attenuate spark.

Also the magnets may be weak. Some of them can be "recharged" but good luck finding someone to do that

Mag parts of that nature can get expensive quick Only thing I can suggest is look around in your area "for some old guy" who knows mags and really knows how to make them tick.
 
Take the cover off, see if everything looks Kosher. I`d be interested to see what it looks like. My mag experiences are with 4 cyl. welders. coils do go bad and are salty.
One thing I`ve learned they should have solid core plug wire/s.
 
Thanks for the reply’s
Will pull cover and post pic
I think everything is original but looking on eBay I can’t see putting $150 for a replacement
Cool unit but heavy.
Made in USA

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If you keep that Wisconsin, the mag will only be the first of your problems. I've worked on a variety of Wisconsin motors from the singles to the larger V-4's. You soon find out that Wisconsin is synonymous with misery. Any way you can adapt a current engine to the alternator? You're only looking at about 3-4 hp.
 
6PakBee said:
If you keep that Wisconsin, the mag will only be the first of your problems. I've worked on a variety of Wisconsin motors from the singles to the larger V-4's. You soon find out that Wisconsin is synonymous with misery. Any way you can adapt a current engine to the alternator? You're only looking at about 3-4 hp.
Click to expand...
In fact as old as that one is, it likely does not even have diode rectified field. It may be a dc generator to produce field current, meaning commutator/ brushes to wear, or it may be the old selenium rectifier stack. Plus the genset winding/ wiring insulation is "just that old"
 
There are videos on rebuilding FB mags on U tube. I just did my mag on a older Lincoln welder.....
Id make sure there is no oil inside mag, meaning a failed oil seal. You mention new points and condenser
As long as the cap and rotor are in good shape and the points are clean and properly gaped, my thoughts are a failing coil.......I had exactly that happen on mine. I replaced everything but the coil and yet I had a weak erratic spark
My coil looked ok, no cracking. I checked it with a ohm meter and the readings were not as indicated
I replaced it and that did the trick
Good luck
 
Steve welder said:
I replaced everything but the coil and yet I had a weak erratic spark
My coil looked ok, no cracking. I checked it with a ohm meter and the readings were not as indicated
I replaced it and that did the trick
Good luck
Click to expand...

On that note, ohm readings are not very dependable for coil ttroubleshooting. A few partially shorted turns in either primary or secondary will never be detected, and moisture ingress causing a high voltage leak won't show up many times on a meter, either Even a "Megger" I have one 500V and 1000V and it is not enough to test coil insulation--as they generate much more in operation

If you don't have some form on specialized coil tester, you have to just "guess."
 
67Dart273 said:
On that note, ohm readings are not very dependable for coil ttroubleshooting. A few partially shorted turns in either primary or secondary will never be detected, and moisture ingress causing a high voltage leak won't show up many times on a meter, either Even a "Megger" I have one 500V and 1000V and it is not enough to test coil insulation--as they generate much more in operation

If you don't have some form on specialized coil tester, you have to just "guess."
Click to expand...
I suspected the coil and I took readings on the old one compared to the new one and there was a big difference, plus as said according to what I read on line something appeared wrong
Decades ago the mag went bad on my SA200 Lincoln welder, there was no internet and so I thought the thing was complicated and I needed the machine running asap
I found a Mag shop and bought a rebuilt. All I recall, it wasn't cheap. Fast forward to a couple of months ago and thanks to the internet I found two excellent video's on rebuilding it, plus many parts vendors.
 
It has points, all older gas engines had points, ive never came across one that didnt until they eliminated points and went with breaker less ignition
The problem with old stuff like this generator is sometimes its expensive to fix just to find if the generator is putting out.....Ive been there numerous times and its a gamble and maybe better to put it to the side until a cheap or free used mag can be sourced
My mag and I understand most have a spring loaded impulse devise that spins the mag fast as you turn over engine and in that one second it creates a strong spark....
My 4 cylinder has a hand crank and most likely could never crank it over by hand fast enough to start but the impulse device in the mag solves that problem
It could really it could be a lot of issues with the mag why there is no or weak spark
 
Yes going to put it into a corner of the garage until the spring or until I trip over it To costly to repair $200 ish and no guarantee it will start or even generate power. Right near a General Engine also inherited
Fan in background is not part of engine
Will still post a pic of mag with cover off
Thanks to all who replied

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