magneto timing a A-C B

There should be two marks on the flywheel. My '42 B is marked as follows:

CENTER - this is when #1 piston is in the top dead center position (either compression or exhaust stroke). When #1 is TDC on compression, the magneto impulse coupling provides a retarded spark from the magneto at this position to start the engine.

FIRE - this is located on the flywheel at 30 crank degrees before #1TDC. It is at this location that the magneto provides an advanced spark at engine running speeds.

You SHOULD have similar marks on your flywheel. They are located on the periphery of the flywheel and are observable through the 1" dia (about) hole on the left side of the torque tube between the upper and lower equipment mounting holes.

The fiber gear in the FMJ (I assume you are talking an FMJ mag) has two marks on it. They can be VERY difficult to see. Use a magnifying glass and wipe the gear face carefully. Do NOT use any kind of solvent or you might eradicate them altogether. The "C" mark is adjacent to the valley between two teeth. It gets aligned with the marked tooth on the small steel drive gear. That tooth should have a chamfer on the gear face.

For internal timing of the mag and timing to the engine, see this pdf file. When timing to the engine, make sure you are on the #1 compression stroke and not the exhaust.

Rod

Yes, #1 cylinder is the one closest to the radiator. The cylinders are numbered 1,2,3,4 in order from front to rear. The actual firing order is 1,2,4,3. Thats how you install your ignition wires from the mag to the sparkplug in a clockwise rotation looking at the mag cap: #1 goes in the socket at the 10 o'clock position, #2 at 1 o'clock, #4 at 4 o'clock and #3 at 7 o'clock.

Rod