Previously, we touched on a few variations in design, but there are plenty more.
Almost all flathead engines had aluminum pistons with a 4 ring design; the top two being compression and the bottom two oil control. From 1935 through 1940 both compression rings were 1/8 inch thick (.125”) and the oil control rings were 5/32 of an inch (.15625”). In 1941, the top compression ring was changed to 3/32 of an inch (.09375”). In 1942, both compression rings were changed to 3/32. This configuration was used through 1959 in the US. Foreign built cars had some exceptions to this. When you want to order rings alone for your prewar car, we need to know these dimensions to get you the correct rings-if available. Only the late configuration of 3/32”,3/32”,5/32”,5/32” is readily available. All other versions are NOS only.
1951 brought other changes aside from the internal bypass mentioned in Part 1. Cam snout diameter was increased from 1 inch to 1-1/8 inches. Accordingly, the flange that mounts to the end of the cam was changed. Also, the fan belts were made narrower. Radiator pressures were also increasing. Through 1948, the cooling system was non-pressurized. In 1949, a new cap with a 4 pound pressure was installed, effectively raising the boil-over point. In 1951, this was increased to 7 pounds and later to 14 pounds.
All engines covered here used Auto-Lite supplied ignition systems. If you look at our catalog, you will notice four distinct tune-up kits listed for passenger cars. From 1935-1938, the points were a two part setup with a threaded base stud to allow gap adjustment. Later versions had more conventional point sets. Parts differ through the years. There are three different distributor caps, two different rotors, three different point sets and four different vacuum advance units. Additionally, later distributors are an easy fit into early cars. This is why it is so important to provide your distributor number. Below you can plainly see a sample distributor number.
Of the numbers listed, the Auto-Lite number provides the information we want. In the picture, the Auto-Lite number is IAT-4101. The configuration will always be three letters, the first being an I, followed by four numbers (I xx-####). Unfortunately, this tag faces the engine making it difficult to read. The simplest way to get this number is with a cell phone camera. Stick the phone in the gap and snap away!