How To Clean Pcv Valve Without Removing

How to Clean PCV Valves And Check Out Crankcase

Apparatus Maintenance

After discussing the legal requirements for the control of gasoline engine crankcase emissions and the use of PCV valves last month, we shall continue in this column by discussing the maintenance of these valves.

The PCV valve most used on fire apparatus is shown in Figure 1, which is a Donaldson valve. This valve is made to be taken apart for cleaning. A solvent such as kerosene should be used and all parts carefully dried before reassemblv. A click should be heard when the valve is shaken after cleaning. The tubing used from the valve to the intake manifold should be cleaned of oily residue before replacing. Also, clean with a solvent the oil filler cap and screen. Dry with an air hose, if available, and oil with clean motor oil before replacing.

Figure 1. PCV valve for large gasoline engines, showing low vacuum position during medium and high speeds at left and high vacuum position during idling Speed at right

—courtesy Waukesha Motor Co.

A type of PCV valve that cannot be disassembled is used by some manufacturers as shown in Figure 2. After washing in a solvent, if the valve assembly does not click when shaken, replace it with a new one.

Figure 2. PCV valve that cannot be taken apart, showing plunger in medium or high speed position at left and idling speed position at right.

A third design is shown in Figure 3. This valve is disassembled by removing a snap ring and washer. The plunger and spring can then be removed for cleaning.

Check at each oil change: Preventive maintenance requires that the engine crankcase emission control system be checked at each oil change. This is best done with a small instrument made for this purpose and available at most auto supply jobbers. The cost of this instrument is nominal, less than $10.

Without this instrument, one method of checking is to idle the engine and, when warm, remove the PCV valve from the valve cover on top of the cylinders or from the crankcase, where it is sometimes installed. With the PCV valve still connected to the tubing going to the intake manifold or the carburetor air inlet, place your finger over the open end of the PCV valve. A strong suction should be felt, and as you alternately place your finger over the opening and remove it, a corresponding change in engine idle speed should be noted.

Figure 3. Another type of PCV valve, which can be taken apart by removing snap ring and washer, in idling speed position (left) and higher speed position (right).

If there is no change in engine speed, the emission control system is partially or completely plugged, and it must be cleaned. At idle speed, the vacuum in the intake manifold is highest, making this test an easy one. At idle, the high vacuum nearly closes the passage for gases, and as the engine speed increases, the vacuum decreases, allowing an increase in passage area through the valve. This is necessary as the blow-by increases with engine speed, and the valve must accommodate a greater volume of gas and air.

Manometer needed: The limit for vacuum in the crankcase is 1/2 inch of water, and the maximum pressure is 1/8 inch of water. The test requires the use of a simple manometer, as shown in Figure 4. A piece of plastic tubing is mounted on a board, as shown, and a graduated scale is marked on the board in 1/8-inch graduations. The tube is half filled with water, colored with a vegetable dye for easier reading, to a level marked 0. The long end is provided with a fitting that will connect with a tapped hole (1/8-inch pipe thread) at a point in the lower part of the crankcase. If no tapped hole is available, do not drill and tap for the connection without first removing the oil pan to prevent any chips getting in the engine lubricating system.

On some engines, the PCV valve is omitted and tubing from the crankcase to the carburetor or the air cleaner is used. A metered opening is provided either at the carburetor inlet or in the air cleaner to control the flow of gases. Simple, yes, but it too requires maintenance. First, the metering orifice is rather small and clogs readily. Second, if the outlet is into the air cleaner, a small filter is provided to keep most of the gummy residue off the air filter. This small filter is a cleanable type and must lie serviced regularly. With (his system, more attention must be paid to keep the carburetor clean.

Figure 4. Manometer utilizes water column in tube to measure vacuum or pressure in engine crankcase.

—courtesy Waukc ska At of Motor Co.

The enforcement of these rules is a responsibility of each state. California has had these regulations for several years, and New Jersey and New York are setting up inspection schedules to start this year. No longer can we neglect this part of preventive maintenance, as fire apparatus is not exempt from these requirements.