In order to prevent the walls of the cylinder from becoming red
hot, it is necessary to cool them by some means, and this is done
by surrounding the cylinder with a _water jacket_ through which the
cooling water is circulated.
[Illustration: Fig. 31--A Diagram showing piping and direction of
circulation in a One-cylinder Water-cooled Motor.]
In order to prevent the water from boiling and evaporating, thus
making the constant addition of water necessary, a _radiator_ is
introduced into the system. This radiator is made up of very thin tubes
which give up their heat rapidly, thereby keeping the temperature of
the water below the boiling point. A fan is also used sometimes to
draw the air through between the tubes, thereby making the process of
cooling take place more rapidly. The system is so arranged that the
water is drawn from the lower part of the radiator where the water is
coldest by means of a pump and forced up through the water jackets and
back into the radiator again. Several different styles of pumps are
used, but a very common one is the _gear pump_ shown in Fig. 32. As you
will see by the drawing, it consists of two gears en mesh with each
other which revolve in the direction indicated by the arrow. The water
entering through the inlet pipe is drawn around the outside and forced
out through the outlet at the top.
[Illustration: Fig. 32--A Gear Water Pump.]
[Illustration: Fig. 33--Front End of Motor, showing radiator, fan and
cam shaft gears.]
[Illustration: Fig. 34--A typical Radiator.]
[Illustration: Fig. 35--Valve side of a Four-cylinder Motor.]
[Illustration: Fig. 36--Opposite side of same Motor showing Carburetor
and Inlet Pipe.]
[Illustration: Fig. 37--Bottom view of same Motor with oil pan removed
showing Crank Shaft, and Connecting Rods.]
[Illustration: Fig. 38--Top view of same Motor showing Valve Caps and
Holes for Spark Plugs.
NOTE--Both views show motor mounted in ring frames used for
assembling in factory.
]