Figure 3-6. Combustion Chambers.
b. Construction (Fig. 3-11). Crankcases in
commonly are mounted by securing the cylinder
head to the crankcase with long studs, and
air-cooled engines are made of aluminum be-
sandwiching the cylinders between the two.
cause it has the ability to dissipate large quantities
Another way of mounting the cylinders is to bolt
of heat. There is usually a removable lower half to
them to the crankcase, and then secure the heads
the crankcase that holds the reservoir of lubrica-
to the cylinders.
ting oil. It commonly is referred to as the oil pan.
On air-cooled engines, the oil pan usually is cast
aluminum. Its surface is covered with fins. The oil
3-4. Crankcase - Air-Cooled Engines.
pan on an air-cooled engine plays a key role in the
removal of waste heat from the engine through its
a. General (Fig. 3-11). The crankcase is the
basic foundation of all air-cooled engines. It is
made as a one- or two-piece casting that
supports the crankshaft, provides the mounting
surface for the cylinders and the oil pump, and
has the lubrication passages cast into it.
Figure 3-7. Valves and Ports.