A valve cover gasket is a seal for the protective valve 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. Some valve covers are sealed against the intake manifold with a liquid sealant, while others feature a gasket. Depending on the number of cylinders in your engine, there might be one or two valve covers and gaskets.
As with most gaskets and seals on an engine, the valve cover gasket is prone to wear over time. When it deteriorates, the seal between the valve cover(s) and the intake manifold is compromised and oil can leak from the engine. The gasket can fail due to overheating, overtightening, frequent changes in temperature, contamination, or a mere lack of use. You might suspect that a valve cover gasket 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 gasket, 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 gasket 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. Care must be exercised to avoid damage to either the mounting flange on the intake manifold or to the valve cover. Old sealant material, whether a liquid type or a gasket (or both) must be removed from the mounting surfaces of both components as well. The technician might also check the mounting flanges to make sure they are straight and undamaged.
Once the intake manifold and valve cover have been prepped, the new gasket is put in place. The 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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