Interesting, I was thinking up until the 40s, didn't expect into the 50s.
Purolator invented the full flow oil filter during WWII. It got used in good new designs after the war, but there were lots of pre-war designs still around. Chevrolet used the straight six stove bolt engine, originally developed in the 20s, as their only engine after the war (other GM divisions had their own engines, also mostly pre-war designs) until the small block came out in the mid 50s. It's notable for not having a fully pressurized oiling system, rods are splash lubricated. Sometime in the 50s, it got fully pressurized oil, and rod bearings that are modern shells, instead of babbit cast integral with rods.
Also, of course, cars were just plain **** at this point, and rarely died because the engine wore out from dirty oil, they died because the oil got burned, leaked out, or something else broke. So the lack of engine oil filtering wasn't a terribly big problem, yet.