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TM 5-685/NAVFAC MO-912
(2) Inspect moving parts as follows:
each part for an engine should be available.
(a) Crankshaft for out-of-alignment condi-
e. Parts salvage. Certain parts may be replaced
tion; journal surfaces for highly polished condition
prior to their failure due to a preventive mainte-
and absence of scratches, nicks, etc.; and counter-
nance program. It may be possible to restore these
weights, gears, and flywheels for proper condition.
parts to specified tolerances. Refer to specific manu-
Verify that crankshaft complies with manufactur-
facturer's literature for recommendations and in-
structions. The following information is a general
er's requirements. An engine crankshaft is a costly
and vulnerable component. Special care in handling
(1) Worn pump shafts and cylinder liners may
is required. Accurate alignment is essential to good
be built up and machined to specified dimensions.
engine operation. Removal or installation may re-
(2) Grooves in pistons may be machined and
quire hoisting. Refer to the manufacturer's instruc-
tions for details and proper procedures.
oversize rings specified for use.
(b) Main be arings for highly polished condi-
(3) Press-fitted bushings and bearings may
tion, cracks, deformation and absence of scratches,
loosen. The related body part may be machined to a
nicks, etc.
new dimension and oversize bushings and bearings
(c) Thrust bearings for cracks and deforma-
tion; surfaces for smoothness and absence of
(4) Worn journals on crankshafts and cam-
scratches and nicks.
shafts may be built up and machined to specified
(d) Camshaft cams and cam faces for worn or
deformed condition; journal surfaces and bearings
3-13. Gas turbine engines.
for highly polished condition and absence of
scratches, nicks, etc; and cam contours and cam
The following provides a general description of gas
followers for good condition.
turbine engines used for power generation. Informa-
(e) Connecting rods for cracks or other flaws
tion is also provided in paragraph 3-lb of this
by magnaflux or dye penetrant method and for
manual. For generating electric power, a turboshaft
bending and for parallelism; bearings for highly pol-
(shaft turbine ) engine is used (see fig 3-19). In a
ished condition and absence of scratches, nicks,
turboshaft engine, the turbine provides power in
cracks, and deformation.
excess of that required to drive the engine compres-
(f) Pistons for cracks and warped condition;
sor. The excess power is applied as rotary driving
verify pistons, rings, and pins comply with manu-
torque available at an output shaft. The power to
facturer's requirements; and rings and pins for gen-
drive the output shaft is extracted from the same
eral good condition.
turbine that drives the compressor. The turbine is
(g) Timing gear mechanisms for good condi-
usually connected through a gearbox to the genera-
tion; backlash for manufacturer's tolerance require-
tor. The gearbox is used for speed reduction.
ments; and gear teeth for general good condition.
(h) Auxiliary or accessory drives for good op-
3-14. Gas turbine engine classifications.
erating condition. Consult the specific manufactur-
er's literature for instructions.
a. Pressure and stages. Gas-turbine engines used
d. Repair parts and supplies. Certain repair
for auxiliary power generator sets are classified as
parts and supplies must be available for immediate
high-pressure-turbine (HPT) or low-pressure-
use. Refer to specific manufacturer's literature for
turbine (LPT) types. Additionally, the engines are
recommendations. The following information is a
classified by the number of stages employed in the
general guide:
turbine design. In general, the more stages used in
the design, the greater the engine torque. All of the
(1) The following parts should be renewed at
turbine rotor stages in the multi-stage turbine are
each: gaskets, rubber sleeves, and seals. Adequate
quantities should be maintained.
connected to a common shaft.
b. Power requirement. For a specified prime
(2) The following parts have a reasonably pre-
dictable service life and require replacement at pre-
mover power requirement, the engine design can be
dictable periods: fuel injectors, pumps, governors,
either a single-stage, large diameter turbine or an
equivalent small diameter multi-stage turbine.
and valves. A one-year supply should be main-
c. Simple cycle. Most engines are designed to use
natural gas and/or liquid fuel similar to kerosene.
(3) The following parts have a normally long
These are called simple-cycle engines.
life and, if failure occurs, could disable the engine
d. Compressor and combustor. Most engines have
for a long period of time: cylinder head, cylinder
an axial flow compressor and a cannular or annular
liner, piston and connecting rod, gear and chain
combustion section (combustor).
drive parts, and oil pressure pump. One item of

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