Found: URGENTLY - Fan Pulley Ford Lynx 12V Generator

[Tony Smith]

Originally Posted by Lynn Eades

A Ford part number is usually made up of three parts:
Here is a basic run down.
The root number (eg 10130) refers to a generator pulley.
The prefix (eg 01AS) which denotes country and year of origin and particular vehicle application. (I have no reference material to decode the 01AS. This may mean the part is specific to the Lynx armoured car)
The last part is the suffix (in this case a "D")
The "D" denotes changes or improvements in that item and so you might have a pulley that to all intents is the same. however they may have added material to strengthen the design, improve the air flow from the fan, or maybe even dynamically balanced as opposed to a static balanced original (just trying to come up with examples) Each time a design improvement is introduced, the suffix changes.
Someone like Tony Smith will be able to explain this in more detail.

01A is the model code for a 1940 model standard Ford car. the "S" denotes a special part. To my eye, it may relate to the belt width, which looks in the pics to be wider than the regular "Wide belt". The Suffixes A, B, C, etc usually denote variable or interchangeable parts, in this case would be for pulley diameter.

Originally Posted by Tony Wheeler

"This led me to consult the parts list, whereupon I discovered there were in fact two different diameter pulleys fitted, nominally 3 1/2" and 4 1/2", the explanation for the smaller one being: "Use where low cut in speed is desired."

What this means is that the refers to the engine rpm when the Regulator Coil will close and provide charging current to the battery. A smaller pulley relative to the Crank pulley will turn the Genny shaft at higher rpm. The voltage output of the Genny will exceed Batt Voltage at a lower engine speed than with a larger Genny pulley. Generally, the larger pulleys were fitted to cars where engine speed would be quickly increased when driving, and usually sit at a higher cruise rpm. Light commercials and heavy trucks would be specified with progressively smaller pulleys, as these vehicles spend more of their duty cycle in lower rpm ranges.

In Ford Military Vehicles, the smaller pulleys were specified for vehicles that would spend time idling so that the Genny would spin fast enough to charge the Battery at high idle speeds. Typically Radio equipped vehicles, or those that made use of the PTO for a specific function.

I do have a list of the various sized pulley part numbers in both Single and Twin belt varieties.