When repairing a tractor magneto, remove it from the tractor and clean it, along with the screws and base, as thoroughly as possible, avoiding the black plug that makes the spark and the armature. Dry them, and then reset the magneto's timing. Test for a blue and white, 1/4-inch spark by turning on the engine. Reassemble the magneto in the opposite order it was removed.
Before removing the magneto, use WD-40 to lubricate all screws and nuts. Remove the screw that secures the wire, and then displace the plug to which the wire was connected. While removing it, clean the black pick-up located at the bottom.
Take out the screws on each side of the strap that holds the magnet in place. Hold down the base while pulling out the magnet; tap it with a rubber hammer if it does not come off by hand. Use a wrench to take the nut from the shaft, and take out the gear.
Take off the screws that hold the cap in place, and then use a screwdriver to take off the cap. Remove the armature. Wipe it down, place it aside, and then clean the other parts with soap and hot water. Pat them dry, and allow to air dry fully. To restore the magneto, the parts can be painted by using clear or aluminum paint on the base and black paint on the magnet itself.
Once dried, reassemble, and set the timing. On a 35 degree lug magneto, move the index trip ring 4 1/2 marks from the top position; for a 25 degree lug, move it 1 1/2 marks. Tighten the retaining screws, and test for a usable spark before fully remounting to the engine.