So I'm trying to find the part number on the differental on my '49 F1. I cleaned it off fairly well and found (while looking from the rear) that there is a patent number on 2 of the 4 tabs, a 6 digit number on the top left tab, and nothing on the bottom right. It should be either a 3.92 or a 4.27, the manual says the part numbers are OM-4209 and 8M-4209-B, respectfully.

Does anyone know or recall how to tell which gear size it would be?

 

Hi James,

Couple of questions...Do yo have a 3 speed or 4 speed transmission (not even sure the 4 speed was an option yet on the 49 but thought I'd ask). I know you are not running at the moment

If nothing else, you could jack up the rear end and see how many times the drive shaft turns to get one full rotation of the rear wheel - almost 4 or 4 1/4 turns.

 

It's a three speed. I'll have to talk my neighbor into coming over and turning the rear wheels for me while I count the shaft rotations. I'm sure he'll be up for having a beer some night!