Timing a mag. (FMJ)
1. If you have taken the Mag. apart, the internal gears need to be timed. (Set points at .020)
2. Remove the large cap and line the C mark on the fiber gear with the marked tooth on the steel gear. Tip- turn the engine backwards to get the steel gear tooth to stop straight up and position the C mark on the fiber gear straight down. This times the rotor to the points. It is pretty simple in theory. Like all four cycles, the piston comes to TDC (top dead center) twice for every time the magneto or distributor rotor goes around. ("B"&"C")The left side of the engine has a hole in the bell housing where you can see the timing mark on the flywheel. ("WD" &" WD45" The timing mark is found by looking under the flywheel housing for a small hole possibly covered by a small plate held with two wing bolts. The FIRE mark and the TDC mark are located on the flywheel through this hole. Use a little light colored paint to make seeing them much easier). 3. Take out the #1 spark plug, and put your thumb over the hole while hand cranking the engine(best to have all the plug wires off while doing this so the tractor doesn't try to fire) , the cylinder will force air past your finger on the compression stroke. (The other FIRE is the exhaust stroke and has the exhaust valves open so no air will come out of the plug hole).
4. When you feel the air coming past your thumb, look for the FIRE mark on the flywheel. When this mark is centered in the hole, the rotor on the mag should be just lower than the #1 lug on the mag. Looking at it as a clock, #1 lug should be near 10:00. Just before the lug is a plastic stud called the timing stud. Perfect timing is when the rotor points to the timing stud while the FIRE mark on the flywheel is centered in the hole. 5. If your rotor points to 5:00 your mag is 180 degrees off and needs to be removed and the coupling turned till you achieve 10:00. If it is not right on the timing stud, you can loosen the mag and rotate it until it is. 6. Put it all back together and time your spark plug wires 1-2-4-3 clockwise on the magneto cap.
Remember if the rotor is aligned with the timing lug when the fire mark is in the window, you got it right. If it's not quite aligned when the fire mark is in the hole, then you rotate the mag clockwise or counter clockwise until it is. Remember Perfect timing is when the rotor points to the timing stud while the FIRE mark on the flywheel is centered in the hole.
This is a comment from a #1 AC mechanic: Timing Mark skipwelte NW IA 7/17/2002 5:27:27 PM Roll the eng over until the points just start to break on #1 cylinder compression. The bolt on the front pulley should be at the 12:00 position. Now remove the cover at the bottom of the hogshead, timing mark should be visible. If not, roll the eng 1/2 turn one way or the other, if timing marks show up, then youve got an early WC flywheel. WCs without starter had timing marks that showed up on the Top of hogshead, not on bottom. Someone may have added starter ring gear to an early WC. This fooled me also a time or two.