I have two early 1938 B's, B7749 and B8452 that have sit out for many years.  I would like to make one operational B out of the two parts tractors.  My question is about magnetos.  One has a FMX4B3 and the other one has an FMK4B4.  Are either one of these correct for an early B?  I read that when B's were first produced, they had FMK magnetos on them.  I also read that the FMX was a much later magneto that was produced at the end of Fairbanks Morse's production of magnetos.  I would like to know if either of these would be accurate for my B restoration before I try to rebuild one of them or do I need to get and FMJ4B3?

Thank you

As you mentioned, the FMX is the last Magneto Fairbanks made before Distributors came along. Fairbanks improved the "J" series Mag by releasing the "X" in its place. The "X" got rid of all the quirks the "J" series Mags had. One of the main improvements was moving the fiber timing gear from the lower cover to the breaker plate. This upgrade eliminated the need to internally time the fiber gear with the drive gear before the lower cover was installled. Both gears where on the breaker plate allowing the lower cover to be removed to service the unit without taking it out of time. One of the other big improvements was moving from the old style tar taped Coil to the new R2477 Epoxy Coil. The newer Coil is Maroon in color.  Stick with the FMX for your resto.

Steve@B&B