Farmall Cub

I’ve noticed my 1948 Cub has only two shoulders on the distributor shaft that opens the points. Never saw this before on any other distributors, any comments welcome.
Bernard,
Donegal Cub.

That shaft turns at crankshaft speed. Two cylinders need to get a spark each crank revolution. The shaft that holds the rotor is geared to this shaft to run at 1/2 speed. Thus it makes one revolution for each 2 of the crankshaft and has 4 distinct positions where a spark occurs during 2 crank rotations.

It is common for a magneto to have a main shaft that rotates 1/2 revolution each time the engine requires a spark. The rotor has to be speed-reduced according to the number of cylinders in the engine.

Thanks Jim, sadly I’m not enough of a mechanic to understand the information in your comprehensive reply. I was just wondering if this was unusual for a Cub, or is it quite common. By the way the Cub is running sweet.
Bernard,
Donegal Cub.

Hi,
If you have a Cub with a magneto, that is how they are made, with 2 bumps on the shaft, to open the points. Every Cub with an IH magneto is made that way.
The Battery Ignition unit, which came out in 1950, has 4 bumps on the shaft. Some Cubs with magnetos were converted to Battery Ignition units after they came out.

Below is a pic of a magneto from TM Tractor.

That’s exactly like mine Glen, except it has an outside 12 volt coil and it is started and kept alive by a 12 volt battery. I’m not sure what the points should be set at for this setup?? I’m sure someone will chime in and tell me.
Bernard,
Donegal Cub.

.013 thousands of inch, assuming it's an IH manufactured magneto.

Thanks Eugene,