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Distributor cams./ shoulders.

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Donegal Cub
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Distributor cams./ shoulders.

Postby Donegal Cub » Tue Jul 10, 2018 3:44 pm

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,
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Jim Becker
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Re: Distributor cams./ shoulders.

Postby Jim Becker » Tue Jul 10, 2018 3:56 pm

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.

Donegal Cub
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Re: Distributor cams./ shoulders.

Postby Donegal Cub » Tue Jul 10, 2018 4:51 pm

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.

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Glen
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Re: Distributor cams./ shoulders.

Postby Glen » Tue Jul 10, 2018 5:23 pm

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.
Attachments
Cub magneto 5.jpg

Donegal Cub
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Re: Distributor cams./ shoulders.

Postby Donegal Cub » Wed Jul 11, 2018 11:12 am

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.

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Re: Distributor cams./ shoulders.

Postby Eugene » Wed Jul 11, 2018 11:27 am

.013 thousands of inch, assuming it's an IH manufactured magneto.
I have an excuse. CRS.

Donegal Cub
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Re: Distributor cams./ shoulders.

Postby Donegal Cub » Wed Jul 11, 2018 11:58 am

Thanks Eugene,


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