In Reply to: Re: 9N pto cap posted by Kirk-NJ on September 15, 2017 at 04:59:20:
Well, yes, any time a part was changed, even for a minor thing like the material spec, the basic part number would reflect with a suffix or prefix like "A" or "B" or "C" or "D" when the revision was made and effective. For example, the early 9N's offered an optional plastic seat made from soybean polymers. P/N 9N-400-A, (steel), and 9N-400-B (plastic) are both listed in the March 15, 1940 MPC. Other examples are the generator pulleys, generators, and hoods. When the aluminum hood was changed to steel, the part number indicated this with the letter suffix. P/n 9N-16612-A was the aluminum hood using the snap-in battery cover. The 9N-16612-B was the steel hood with snap-in battery cover. The 9N-16612-C was the steel hood with the hinged battery cover. There has to be a documented system of part identification. I see no reference made to the aluminum early PTO-cover in MPC's nor John Smith's site. I would go out on a limb now and a say they were strictly aftermarket, probably offered when the 2N-726 cap was released for early 9N owners. I am not the expert though, maybe Barkley or Smith can chime in.