Positive Crankcase Ventilation: Description and Operation

CRANKCASE VENTILATION SYSTEM
The crankcase ventilation system which is an integral part of the air supply to the engine combustion chambers, is often overlooked when diagnosing problems associated with engine performance. A blocked ventilation pipe or filter or excessive air leak into the inlet system through a damaged pipe or leaking gasket can effect the mixture, performance and economy of the engine.

Emission Control System:

PURPOSE AND OPERATION
The purpose of the crankcase ventilation system is to ensure that any noxious gas generated in the engine crankcase is rendered harmless by burning in the combustion chambers as follows:

Oil laden noxious gas in the engine crankcase is drawn through an oil separator (3) located on the right cylinder head rocker cover, where the oil is separated and returned to the sump. The gas flows through a restrictor in the three way connection (1) and into the inlet plenum chamber where it is drawn into the combustion chambers and burned. The volume of fresh air which is drawn from the atmospheric side of the throttle butterfly to mix with the gas, depends on the position of the throttle and the engine speed.

The air filter (2) fitted to the left cylinder head rocker cover, must be maintained in clean condition to be sure sufficient air enters the crankcase under varying throttle openings and manifold depression, to prevent excessive crankcase pressure or depression developing.