This filter head mounts on the engine block and routes oil to the filter element, then returns cleaned oil to the lubrication circuit. It houses the bypass valve that opens when the filter element is fully loaded, allowing oil to bypass the element and maintain flow to the bearings. A worn or cracked head can cause a pressure drop, leading to inadequate lubrication of the crankshaft and connecting-rod journals. On reinstallation, replace the gasket between the head and the block and torque the mounting bolts to specification.