DESCRIPTION
The positive crankcase ventilation system is designed to prevent contaminating hydrocarbons, created in the crankcase, from escaping into the atmosphere.
Crankcase vapors are routed from the crankcase through a vacuum controlled ventilating valve (PCV) into the intake manifold. When vapors reach the intake manifold, they are mixed with air/fuel and burned in the combustion process.
OPERATION
With the engine operating, fresh air enters the PCV system through the air cleaner assembly. Fresh air flows through the crankcase breather and into the rocker arm cover compartment.
Entering fresh air combines with blow-by gases and unburned air/fuel mixture of the crankcase. Combined gases are drawn into the carburetor, through the PCV valve, by manifold vacuum. Crankcase gases mix with air/fuel mixture and are burned in the combustion chamber. (Scheme 25)
Typical Positive Crankcase Ventilation System. Scheme 25
The PCV valve is held closed by spring pressure when the engine is not running. This prevents hydrocarbon fumes from collecting in the intake manifold, resulting in hard starting.
When the engine is running, manifold vacuum pulls the PCV valve open, allowing crankcase vapors to enter the intake manifold. A baffle in the rocker arm cover prevents engine oil from being drawn into the intake manifold.
If the engine backfires through the intake manifold, the PCV valve closes and prevents any flow of gases through it. This is to prevent the ignition of fumes in the crankcase.
SERVICE PROCEDURES
An engine may idle slow or rough due to a clogged PCV valve or system. Never adjust idle speeds without first checking entire PCV system.
| CAUTION | If a PCV system component becomes clogged, all crankcase ventilation will stop and serious engine damage will occur. |
PCV VALVE
Remove and replace PCV valve every 30,000 miles. Do not attempt to clean valve. Replacement intervals may become shorter under severe service.
FILTER ELEMENT
Filter element should be replaced every 30,000 miles.