[Tony Smith]

It's all that, and more!

The Ford V8 used a wire gauze breather cap (part no 48-6766B) used at the top rear of the inlet manifold, a standardised design that was introduced from the 1934 model and used right through to 1948 on cars and trucks. The wire gauze was an effective filter to prevent wasps getting in the engine, but little much else smaller, even with the gauze dampened with oily blow-by. In 1941, a Service Bulletin announced that a Oil Bath filter was introduced for "Heavy duty service in dusty conditions". I'll go out on a limb here and suggest the standard breather was fine for the paved roads of Detroit or Windsor, but following experiences in North Africa, where Ford engines were required to be rebuilt after as little as 1000Mi due to "dusting" and wear, something was needed that actually filtered the air going to crankcase.

United Specialties made a small air filter that was in use at the time on small engines such as Waukesha, Onan and Wisconsin. This filter had a flat base and was screwed onto the flange with a thumbscrew. Ford released this filter as a stopgap measure as C11AS-6766C, but it required a new filler pipe to accept it, C01Q-6765D. This pipe was offset to allow the larger diameter of the oilbath filter to clear the firewall on the C11ADF wagons and standard cab '41 model trucks, and the engine cover on 12 Cab CMPs. A later version (C11AS-6766B) was modified to use the bayonet fitting of the 48-6766B cap, allowing it to use the standard filler pipe, as there was also more firewall clearance on 1942 model cabs and the 13 cab CMP.