Generator and Fan

[Kube]

Originally Posted by ndnchf

I don't know, I'm not an engineer

There were a lot of different pulleys available over the years. A mid - late 1930s car with big V8 typically used a pulley .408" to .438 diameter. The V8 60 used a 3.68" diameter pulley in '37. In '38-'39 it could be either 3.71" or 3.40" diameter pulley. In 1940, the 01A-1000-B V8 60 generator used either a 3.12" or 3.18" diameter pulley.

On the left is a 1937 V8 60 pulley, 3.68" diameter. PN BB-10130-B. On the right is a big V8 pulley 4.38" diameter. PN 68-10130-C.

I'm guessing you are getting your information from a Ford parts book. Am I correct?
If you are, you must keep in mind, the parts listed are for service and in many cases Ford "made do" with what worked.
In 1940, there were two pulleys regardless of vehicle application. The first design was 3 11/16" diameter. The later design was 3 3/16" diameter.
I'm not certain where you got 3.12 and 3.18. Do you really think Ford made two pulleys that were a mere .060" different from each other?