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Air-Cooled Systems | Up
Construction Mechanic Basic Volume 01 - Construction methods and practices | Next
Liquid-Cooled System |
In air-cooled engines the cylinders are mounted
independently to the crankcase so an adequate volume
of air can circulate directly around each cylinder,
absorbing heat and maintaining cylinder head
temperatures within allowable limits for satisfactory
operation (fig. 6-2). In all cases, the cooling action is
based on the simple principle that the surrounding air is
cooler than the engine. The main components of an air-
cooled system are the fan, shroud, baffles, and fins. A
typical air-cooled engine is shown in figure 6-3.
Fan and Shroud
All stationary air-cooled engines must have a fan or
blowers of some type to circulate a large volume of
cooling air over and around the cylinders. The fan for
the air-cooled engine shown in figure 6-3 is built into
the flywheel. Notice that the shrouding, or cowling,
when assembled will form a compartment around the
engine so the cooling air is properly directed for
effective cooling. Air-cooled engines, such as those
used on motorcycles and outboard engines, do not
require the use of fans or shrouds because their
movement through the air results in sufficient airflow
over the engine for adequate cooling.
Baffles and Fins
In addition to the fan and shroud, some engines use
baffles or deflectors to direct the cooling air from the fan
to those parts of the engine not in the direct path of the
airflow. Baffles are usually made of light metal and are
semicircular, with one edge in the air stream, to direct
the air to the back of the cylinders.
Most air-cooled engines use thin fins that are raised
projections on the cylinder barrel and head (fig. 6-3).
The fins provide more cooling area or surface and aid in
directing airflow.
Heat, resulting from combustion,
passes by conduction from the cylinder walls and
cylinder head to the fins and is carried away by the
passing air.
Maintaining the Air-cooled System
You may think that because the air-cooled system is
so simple it requires no maintenance. Many mechanics
think this way and many air-cooled engine failures
occur as a result. Maintenance of an air-cooled system
consists primarily of keeping cooling components
clean. Clean components permit rapid transfer of heat
and ensure that nothing prevents the continuous flow
and circulation of air. To accomplish this, keep fans,
shrouds, baffles, and fins free of dirt, bugs, grease, and
other foreign matter. The engine may look clean from
the outside, but what is under the shroud? An
accumulation of dirt and debris here can cause real
problems; therefore, keep this area between the engine
and shroud clean.
Paint can cause a problem. Sometimes a mechanic
will reduce the efficiency of the cooling system by the
Figure 6-3.—Air-cooled engine.
6-3
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