Crankcase Ventilation Systems: Operation

Air entering the system first passes through the breather cap, which contains a copper mesh filter to remove air borne dust and foreign particles. It then flows down the oil filler tube and circulates through the engine. The fumes are then routed toward rear of left valve cover. From here they pass through a connector and hose to ventilator valve. The valve is located close to carburetor insulator fitting. The critical point of the system is ventilator valve. When the engine is started, manifold vacuum pulls the valve open against spring pressure and, as long as the engine vacuum is from I-14.9" Hg., the valve "floats", permitting crankcase fumes to by-pass unrestricted and enter intake manifold. During periods of high manifold vacuum (above 14.9"), the valve closes against spring pressure, leaving only a.102" orifice open to the manifold. This prevents large amounts of hydrocarbons from entering the air-fuel mixture and upsetting the fuel-air ratio necessary for smooth engine performance.