What really makes a car go? There are many parts to an engine that
are visible, like an alternator, starter, hoses, wires and a bunch of other
things. But what is in the inside and how does it work? The process is
really just a mixture of parts, moving in sync in a distinct pattern called
the four-stoke cycle.
To understand the components of a four-stroke engine better, a
little background information may be needed. "In a gasoline engine,
exhaust and intake manifolds (tunnels) and valve ports(inlets or outlets)
are needed to supply air and fuel on the intake (first down) stroke of the
cylinders, and to expel burned gases on the exhaust(second up) stroke. The
ports are opened and closed at the proper times by the intake and exhaust
valves, which close against the sides of the ports" (Doyle 128). The
controlling of the valves start with a cam shaft. A cam shaft has lobes on
it which are all shaped differently, but resemble an oval. On a camshaft
lobe there rests a lifter. A lifter is cylinder shaped and pushes up on a
push rod when the lobes are rotating. A push rod, which is connected to a
rocker arm, then "rocks" down on a spring that in turn pushes open a valve.
This all happens due to the rotation of the camshaft which is geared to the
crankshaft (which is connected to the pistons) which is all part of the
four stroke cycle.
The four-stroke cycle starts with the intake stroke. On the intake
stroke, the piston moves down from its top dead center or the farthest "up"
position creating a partial vacuum which draws in the fresh air-fuel
mixture from the open intake valve. Think of the vacuum like a syringe
with no needle. "If you put your finger over the end of the tube and pull
back the plunger, then pop your finger off the tube, the suction will draw
fresh air into the tube" (Freiburger 76). As the piston is moving towards
its bottom dead center or the farthest "down" position, "the intake valve
begins to close. The valve is kept open as long as possible to get ...