• The cylinder head covers and seals the top of the
cylinder. It also holds the valves, rocker arms, and
often, the camshaft.
• The combustion chamber is a small cavity (hollow
area) between the top of the piston and the bottom
of the cylinder head. The burning of the air-fuel
mixture occurs in the combustion chamber.
• The valves open and close to control the flow of
the air-fuel mixture into the combustion chamber
and the exhaust gases out of the combustion
chamber.
• The camshaft controls the opening of the valves.
• The valve springs keep the valves closed when
they do not need to be open.
• The rocker arms transfer camshaft action to the
valves.
• The lifters, or followers, ride on the camshaft and
transfer motion to the other parts of the valve
train.
• The flywheel helps keep the crankshaft turning
smoothly. It also provides a large gear for the
starting motor.
Four-Stroke Cycle
Automobile engines normally use a four-stroke
cycle. Four separate piston strokes (up or down move-
ments) are needed to produce one cycle (complete series
of events). The piston must slide down, up, down, and up
again to complete one cycle.
As the four strokes are described below, study the
simple drawings in Figure 1-9.
1. The intake stroke draws the air-fuel mixture
into the engine’s combustion chamber. The
piston slides down while the intake valve is
open and the exhaust valve is closed. This pro-
duces a vacuum (low-pressure area) in the
cylinder. Atmospheric pressure (outside air
pressure) can then force air and fuel into the
combustion chamber.
2. The compression stroke prepares the air-fuel
mixture for combustion. With both valves
closed, the piston slides upward and compresses
(squeezes) the trapped air-fuel mixture.
6 Section 1 Introduction to Automotive Technology
Figure 1-8. Memorize the basic parts of this one-cylinder
engine.
Camshaft
Lifters
Valves
Combustion
chamber
Piston
Piston
rings
Connecting
rod
Crankshaft
Flywheel
Cylinder
Block
Cylinder
head
Valve spring
Rocker arms
Figure 1-7. The engine can be located in the front or rear of the
vehicle. (Dana Corp.)
Front engine, front-wheel drive
Front engine, rear-wheel drive
Rear engine, rear-wheel drive
Transverse
engine mounting
Longitudinal
engine mounting