Oil returning from the cooler system travels in a cylinder case passage to the oil filter, which is a spin-on replaceable cartridge. The oil filter mounts on a hollow threaded fitting and uses a soft ring to seal against the cylinder case flange (see Figure 3-6).
The oil filter is of the full-flow design, since all oil from the pump and cooler system must pass through it. A valve mounted in the cylinder case allows oil to bypass the filter when the difference in pressure between the inlet and outlet exceeds 16-19 psi. The bypass valve provides lubrication to the engine if the filter becomes extremely restricted.