TM 1-1500-204-23-1
CHAPTER 7
GENERAL RECIPROCATING ENGINE MAINTENANCE
7-1.
General The maintenance instructions and
procedures contained in this chapter are general and
applicable to reciprocating engines used on Army aircraft.
Maintenance instructions that are specific and peculiar to
particular engines are contained in the applicable
maintenance manuals and will be used in conjunction with
general information contained in this chapter.
7-2.
Engine Types and Designations. Reciprocating
engine types and designations are explained in the
following paragraphs.
a.
Types. Types of aircraft reciprocating
engines used by the Department of the Army are the
radial type and the opposed type Radial-type engines
have the crankcase in the form of a circle, as shown in
figure 7-1. The cylinders extend out from the housing in
the same manner as the spokes of a wheel Cylinders are
arranged evenly in the same circular plane and all pistons
are connected to a 360-degree crankshaft. Opposed-type
engines have cylinder banks arranged an two rows
directly opposite each other with a crankshaft in the
center as shown in figure 7-2. Pistons are connected to
the single crankshaft. This type engine may be mounted
with cylinders vertical or horizontal.
Figure 7-1. Radial-Type Engine
b.
Designation Examples. An example of radial
engine designation is R-1820-103. The R denotes a
radial arrangement of the cylinders, 1820 denotes a total
of 1820 cubic inches displacement, and 103 denotes a
particular modification or characteristic of the engine. For
opposed engine designations, such as IGSO-480-A1A6,
the I denotes injected, G denotes geared output drive, S
denotes
supercharged,
the
O
denotes
opposed
arrangement of the cylinders, 480 denotes a total or 480
cubic inches displacement, and the A1A6 denotes a
particular modification of characteristic of the engine.
7-3.
Reciprocating Engine Theory. A reciprocating
(internal-combustion) engine is a device for converting
heat energy into mechanical energy. Gasoline is
vaporized and mixed with air, forced or drawn into a
cylinder, compressed by a piston, and then ignited by an
electric spark. The conversion of the resultant heat
energy into mechanical energy and then into work is
accomplished in the cylinder. The operating cycle of an
internal combustion reciprocating engine, as shown in
figure 7-3, includes the series of events required to induct,
compress, ignite, burn, and expand the fuel-air charge in
the cylinder, and to scavenge or exhaust the byproducts
of the combustion process. When the compressed
mixture is ignited, the resultant gases of combustion
expand very rapidly and force the piston to move away
from the cylinder head. This downward motion of the
piston, acting on the crankshaft through the connecting
rod, is converted to a circular or rotary motion by the
crankshaft.
7-4.
Major Engine Components. Major engine
component types and maintenance are described in the
following paragraphs.
a.
Crankcases. The crankcase encloses the
various mechanisms surrounding the crankshaft. The
crankcase provides a tight enclosure for the lubricating oil
and supports various external and internal mechanisms it
contains the bearings in which the crankshaft revolves
and provides support for attachment of cylinder
assemblies. Finally, it provides mountings for attachment
to the aircraft, and by reason of its strength and rigidity, it
prevents misalignment of the crankshaft and its bearings.
The following paragraphs describe crankcase types and
general maintenance.
7-1
