While we're asking what is the purpose of questions...

JRSutton

Well-known Member
on a 48 wico magneto.

On the magneto cover/cap there's a little round glass window.

what is this used for?

I always assumed it's for timing - so you can see where the rotor is without removing the cover... (though mine is so cloudy you can't see anything through it, so I could never see what I was supposed to see...).

I can't imagine what else it could be.

But I'd like to know for sure - so then when people ask I can actually answer without adding "I think..."
 
I've got an American Bosch mag from a 40's era Waukesha power unit with a similar "window" on one side of the cap.

Directly behind the window is the rotor drive gear. One rotor gear tooth is painted white. When the mag is at TDC #1, the white tooth is centered in the window.

This feature simplifies timing the mag to the engine - no messing with the impulse coupling is required. With the engine at TDC #1 cyl firing, simply rotate the coupling backward until the white tooth appears, then mount the mag.
 
very interesting - thank you!

I've been waiting till I no longer need the tractor for the season to take it apart to take a closer look at it.
 

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