Pic. 8.4. Scheme of the forced crankcase ventilation system: 1 - suction pipe; 2 - air filter; 3 - spool device; 4 – a cover of a head of the block of cylinders; 5 - fresh air; 6 - crankcase gases; 7 - air-fuel mixture
Forced crankcase ventilation reduces the content of hydrocarbons in the exhaust gases by circulating fresh air through the crankcase, mixing it with crankcase gases and directing this mixture to the intake pipe for afterburning in the engine combustion chamber (pic. 8.4).
The system consists mainly of vacuum hoses and a spool device that regulates the flow of gases in accordance with the engine speed and the degree of vacuum at the intake pipe.
Checking the technical condition
The operation of the crankcase ventilation system can be easily checked.
This system needs to be checked regularly as the spool and vacuum hoses tend to get clogged with soot and tarry deposits from the gas stream. When the flow through the spool decreases or stops, the engine idle speed usually decreases and the engine idles erratically.
To check the vacuum in the system, remove the air filter cover and locate the small crankcase ventilation filter, which is located on the inside of the air filter housing.
Disconnect the hose going to this filter.
When the engine is idling, close the hose opening with your thumb - a slight vacuum should be felt. If you gradually move your finger away, you can hear a hiss. This indicates that air is being sucked in along the entire line of the system. If vacuum is felt, the system is working. Check the cleanliness of the filter element. If you suspect that the filter element is dirty, replace it, as this is an inexpensive operation, but ensures the safety of the engine.
If the vacuum at the end of the hose is weak, then the system line is clogged and further check is required.
Turn off the ignition, find the spool device of the ventilation system and carefully remove it from the rubber boot. Shake the spool and listen for a knocking sound (clicks). Knocks are caused by the spool ball. If knocking does not occur with every shaking (knock is not free), replace the spool.
Start the engine and let it idle with the spool removed. Close the spool hole with your thumb and check the vacuum. It should be significant and felt immediately.
If the vacuum on the spool is weak or not felt at all, turn off the ignition and disconnect the vacuum hose from the other end of the valve. Start the engine and at idle check the vacuum at the end of the hose that is disconnected from the spool. No vacuum indicates contamination inside the hose or engine intake. If the hose is clogged, replace it or remove it from the engine and blow it out with compressed air. If the carburetor or suction passages are clogged, these units must be removed and washed thoroughly to remove tar deposits. If the vacuum on the hose without the spool is strong, and at the inlet of the spool with the hose connected, the spool is defective and must be replaced.
When purchasing a new crankcase ventilation spool, make sure this part matches your engine type. Otherwise, too little or too much vacuum may occur, which can lead to engine failure.
Replacing elements
For spool and spool filter replacement procedures, see sec. 2.