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The valve cover covers the valve train. The valve train consists of
rocker arms, valve springs, push rods, lifters and cam (in an
overhead cam engine). The valve cover can be removed to adjust the
valves. Oil is pumped up through the pushrods and dispersed
underneath the valve cover, which keeps the rocker arms lubricated.
Holes are located in various places in the engine head so that the
oil recirculates back down to the oil pan. For this reason, the valve
cover must be oil-tight; it is often the source of oil leaks.
The valve cover is often distorted on older cars, because at some
point the valve cover screws were over-tightened, bending the valve
cover. This happens because the valve cover is made of very thin
sheet metal and cannot withstand the force of an over-tightened bolt.
One way to determine if your valve cover is bent is to remove the
gasket and put the valve cover back on to the cylinder head. When the
valve cover and cylinder head come into contact, the cover should sit
flat. If it rocks, it is bent. Cast aluminum valve covers cannot be
straightened, they need to be replaced. Sheet metal valve covers can
be straightened.
A symptom of a bent or leaking valve cover is a pinching of the valve
cover gasket. This means that the gasket is sealing one area and not
sealing another area. This condition produces a leak; oil could be
leaking down the side of the engine. Some valve covers are hard to
access, because they are covered with other engine parts.
Chronic valve cover leakage can sometimes be fixed by using two
gaskets glued together instead of using just one.
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