S&amp,S Cycle S&S Cycle Standard Diameter Crankcase Breather Reed Valve 31-2096 Consists of 3 steel reeds that are normally in the closed position When pistons travel downward in the cylinders, the air in the crankcase is compressed and pressure in the crankcase below the pistons increases Pressure causes the reeds to open, allowing the air and oil mist in the crankcase to escape into the cam chest When pistons change direction and begin traveling back upward in the cylinders, a vacuum is entering the crankcase A slight vacuum is maintained in the crankcase and oil scavenging is greatly improved