The
head is a self-contained part of most modern
internal combustion engines. The head typically contains the
actuators and
lifters/
rocker arms that connect to and move the
valves up and down to seal and open the
intake and
exhaust paths (also in the head) from the combustion chamber. In an
overhead cam engine, the
camshafts reside in the head and directy actuate the valves. In a
pushrod engine, the camshaft resides in the actual
block and the
pushrods extend from below nto the head and activate the rocker arms and then the valves.
The bottom part of the head typically contains recessed areas that forms the topmost parts of the combustion chambers. The bottom-most parts of the valves are seen here. Usually the spark plugs bolt through the top of the head and the electrodes extend through into this recessed area. The head is then bolted to the engine block (containing the piston and cylinders). The regions formed between the recessed area on the bottom of the head and the block become the combustion chambers, where the magic happens. The interface between the block and the head is typically machined to a very high precision so that a near-perfect seal is created.