Howdy, new guy, new to tractors. I bought my retirement property,it had a dozen or so old tractors. They have to have say 30 years or more. I decided to try to put one back in service, it's a 39 B, hand cranked, mag fired,no electrics anywhere, with a factory sickle bar attachment.

   Motor was of course set up, I got it to turn and it turns pretty free. Got some compression, Cleaned and rinsed the tank, cleaned out the sediment bowl and cleaned out the carb, new needle and seat.

   The mag is giving me problems. Fairbanks Morse J. I sent it to a guy who said he could test it, recharge the magnets and do whatever. Unfortunately the box came apart in the mail and the mag is gone. He sent me a used later model mag, an X? model.  I got one or two backfires out of it before I lost spark in that one.

  I opened it up, the points look like garbage. They don't line up straight, and don't appear to close all the way, like the contacts aren't flat. I also found the screw that holds the contact strip to the coil bottomed out but not securing the strip. I put a washer on and got that right, but spark is very weak.

  Also, the rotor does not point to #1, like the old J model did. I suspect it's off a tooth although I haven't checked the marks yet.

  So can anyone tell me if the later mag is a viable option for this motor? If so I'll try a new set of points. If not there is another J mag in the yard that also won't fire...

The "X" series Magneto is actually the bestest out of the bunch of Fairbanks. The "X" replaced the "J" series. The "J" is a good Mag, but had a lot of quirks such as the timing gear bushing seizing up and spinning in the lower cover boring the hole bigger. Other problems were the tar taped Coils that came in them leaked.

Fairbanks fixed a lot of those quirks the "J" had with the "X" moving the timing gears together on the breaker plate eliminating the bushing issue and the wear issue the fiber gear had with the steel mainshaft gear. The tar taped Coils that leaked eventually were replaced with the better Red epoxy replacement which eliminated the leakage issue. So to answer your question, yes, the "X" is the good upgrade to use next to the Battery ignition system (Distributor) that came later on down the road. 

I do a lot of customer Mag work especially in the Winter months when a lot of our customer's send the Mags in for a "freshen upper".  Point misalignment is a common problem with all the model Mags, and it's important they align perfectly for good performance. Like anything else now a days, Mag parts are getting ridiculously expensive and the quality is slowly goin' down hill as well.  I use F/M components in my rebuilds, but I've already had a few "duds" that I never had before.  The Mags that are in bad shape cost a lot to repair today providing you can get good components..If you need any help or have some questions, I'd be happy to help you out if I can... HTH

Steve@B&B

bb-customcircuits.com