Crankcase ventilation

The combustion gases from combustion chamber may leak into the crankcase which can corrode the engine parts like piston pins, cylinder walls etc. To remove these gases from crankcase, a steady flow of air is carried through the crankcase. The air takes away the combustion products in the form of air or mist. Two methods are generally used for crankcase ventilation.
Road draft system: Air stream from the motion of vehicle is allowed to enter the engine at the top. It is circulated in the crankcase where it takes away with it the products of combustion like mist, vapors etc. This stream of air then goes to the atmosphere through outlet.
Manifold suction system: The filtered air which is used for intake is drawn to the crankcase. There it carries the vapors and exhaust gases with it. Then it is directed to inlet manifold and then to combustion chamber. A valve is placed in between the crankcase and inlet manifold to regulate the supply of air flow as per the engine speed.