A valve cover is a protective cover that allows the engine valves to operate in a clean environment and prevents oil from escaping the engine.
Internal combustion engines such as the one found in most passenger vehicles rely on a set of pistons that pedal a crankshaft the way your legs might pedal a bicycle. The pistons move in response to rapidly expanding gases in their respective cylinders as a result of the combustion process. Each cylinder is sealed air tight so that pressure can build up inside. So, a series of valves at the top of the engine open and close in order to allow air and fuel to enter the cylinders and exhaust gases to escape.
The valve cover allows engine oil to work around the valves and other parts of the valve train without spraying all over the engine compartment and without contaminants entering the engine. Depending on the number of cylinders in your engine, there might be one or two valve covers.
Problems with a valve cover usually stem from a bad valve cover gasket, the seal between the valve cover and the intake manifold of the engine. That said, a valve cover is made of metal or plastic and can become damaged from overheating, overtightening, frequent changes in temperature, lack of use, or contamination. You might suspect that a valve cover is bad if you notice one or more of the following signs:
The valve cover(s) is located at the top of your engine. To replace the component, a technician will first need to remove the upper engine cover and any other shields, guards, cables, or other components that are in the way (including electrical, mechanical, and emission control parts). On larger engines with six or eight cylinders that have multiple valve covers, the intake plenum might also need to be removed (depending on which valve cover is bad).
With all components out of the way, the valve cover retaining bolts securing it to the intake manifold are removed and the valve cover is carefully dislodged from the engine. Old sealant material, whether a liquid type or a gasket (or both) must be removed from the mounting surface of the intake manifold. The technician might also check the mounting flange to make sure it is straight and undamaged.
Once the intake manifold has been prepped, a new gasket (or sealant) is put in place. The new valve cover is inserted and the retaining bolts are installed and torqued to manufacturer’s specifications. Finally, the engine is turned on and checked for oil leaks.
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