In Figure 1-17, note how the cam lobe acts on the
valve train. When the lobe moves into the lifter, the lifter,
pushrod, and one side of the rocker arm are pushed up.
This opens the valve. When the lobe rotates away from the
lifter, the valve spring pushes the valve and other parts into
the closed position.
Camshaft timing is needed to ensure that the valves
properly open and close in relation to the crankshaft.
Either a belt, chain, or set of gears is used to turn the
camshaft at one-half of the crankshaft speed and keep the
camshaft in time with the crankshaft. Figure 1-19 shows
how a timing belt is used to operate the camshaft on our
basic engine.
Intake and Exhaust Manifolds
The intake manifold carries the air-fuel mixture into
the cylinder head intake ports. It normally is bolted to the
cylinder head. Ports in the intake manifold match the
intake ports in the cylinder head. The exhaust manifold, as
its name implies, carries burned gasses from the cylinder
head exhaust port to the other parts of the exhaust system.
Figure 1-20 shows the basic action of the intake and
exhaust manifolds.
Note: With multiport fuel injection, the fuel
is injected into the airstream at the port.
However, the fuel is injected into the
airstream at the beginning of the intake manifold
(in the throttle body) with throttle body injection.
Cooling System
The cooling system is needed to carry the heat of
combustion and friction away from the engine. Without a
cooling system, the piston, valves, cylinder, and other parts
could be ruined in a matter of minutes. The head and
block could also crack from the tremendous heat.
Basically, a cooling system consists of a radiator, water
pump, fan, thermostat, water jackets, and connecting
hoses, Figure 1-21.
The water pump circulates an antifreeze and water
solution through the water jackets, hoses, and radiator. It is
often driven by a fan belt running off of the crankshaft pul-
ley, but may be driven by an electric motor. The coolant
(antifreeze-water solution) picks up heat from the metal
parts of the engine and carries it to the radiator.
The radiator transfers heat from the coolant to the
outside air. A fan is used to pull air through the radiator.
Large radiator hoses connect the radiator to the engine.
The thermostat is a temperature-sensing valve that
controls the operating temperature of the engine. When
the engine is cold, the thermostat blocks coolant flow
through the radiator and speeds warm-up of the engine.
When the engine is warm, the thermostat opens to allow
coolant to circulate through the radiator, thus removing
heat from the engine.
Lubrication System
The lubrication system circulates engine oil to high-
friction points in the engine. Without oil, friction will result
in wear, scoring, and damage to parts very quickly. The
lubrication system basically consists of an oil pump, oil
pickup, oil pan, and oil galleries. See Figure 1-22.
The oil pump is the “heart” of the lubrication system
because it circulates oil through the oil galleries. The oil
galleries are small passages that lead to the crankshaft
18 Auto Engine Repair
Camshaft
sprocket
Timing
belt
Adjuster
pulley
Crankshaft
sprocket
Figure 1-19. The camshaft is turned at one-half of engine
speed. A timing belt is the most common method of turning the
camshaft in time with the crankshaft rotation. Note the part
names.