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 TM 55-1925-204-12
1. Remove a shim of 0.025 in.
NOTE
from both sides, then add three 0.007 shims on each side.
If necessary, for a particular condition,
2. Tighten
capscrews
then
the injection timing may be advanced,
remeasure clearance. It should now be between 0.001
or retarded, as the condition requires .
and 0.0065 inch. If not correct, change shim stack until
reading comes within tolerance.
CAUTION
3. Conversely, if clearance reads
Never change the injection timing by
0.010 in., remove a shim of 0.007 in. from each side to
more than 1o at a time, then check
bring clearance within permissible limits.
engine operation after each such
4. When all shims have been
change. Since the firing pressures of
removed and clearance is greater that 0.0065 in., replace
the cylinders are affected when the time
the bearing.
of injection is advanced or retarded,
5. Repeat steps (1) through (5)
these pressures must be checked after
until all bearings have been checked.
each such change is made (table 1-4).
c. Gear and Cam Inspection.
(1) Camshaft drive gear.
(d) Remove six cotterpins from nuts (10)
(a) Turn engine over slowly with the
on studs in gear rim (9).
ratcheting device, and inspect the gear for worn or broken
teeth.
NOTE
(b) Report a defective camshaft drive
The six capscrews securing cover plate
gear to general support maintenance.
to hub may require loosening. before
(2) Camshaft cam lobes.
hub and shaft will slip.
(a) Inspect cam lobes for excessive
wear, or roughness of lobe surfaces.
(e) Loosen the six nuts (10), then holding
(b) Report defective cam lobes to
gear rim (9) stationary, shift hub and shaft in the direction
general support maintenance.
of engine rotation until the chisel mark on cover plate is
(c) Reverse the procedures in steps b.
o
even with mark for 1 off zero setting for advance. Shift
(1) (a) and (b) above, then proceed to timing the injection,
the shaft and hub in the opposite direction to retard.
if required.
(f) Tighten nuts on studs (tighten
d. Timing System. The timing (gear train) system
capscrews on cover plate, if loosened) then install
begins with the crankshaft drive gear, which drives the
cotterpins in nuts and studs.
idler gear, which, in turn drives the main camshaft gear.
(g) Install cover (1) and gasket (2).
The idler gear drives the air distributor by the air
(h) Install timing gear train covers on
distributor intermediate gear, to which is bolted the air
upper base.
timing camshaft gear. Backlash of gears may be checked
(i) Operate engine and check pressures.
by referring to table 1-2 for allowable limits.
The
(j) Repeat the procedures in steps (a)
camshaft gear is composed of a gear rim, gear hub, and
through (i) until adjustment is correct for the. condition.
cover plate. The hub is securely keyed to the camshaft.
The gear rim is locked between the cover plate and hub
4-18. The Engine Electrical System
by means of six studs and nuts through slotted holes in
a General. The engine electrical system consists of
the gear rim. These slotted holes allow the hub and
the instrument panel, with tachometer indicator, fuel
camshaft to be shifted in relation to the gear rim, to adjust
pressure gage, oil pressure gage, starting air pressure
the timing of the engine. Adjust engine timing as shown
gage, water pressure gage, and the pyrometer. In
below.
addition, there is the safety visual indicator, for sounding
(1) Timing the engine fuel injection.
an alarm when the oil pressure or water temperature is off
(a) Remove timing gear train covers
the norm.
from aft end of the upper base.
b. Fuel Pressure Gage.
(b) Use the ratcheting device and turn
(1) Removal. Disconnect fuel line from rear
engine over until the number one piston is at top dead
of gage (1, fig. 4-16), remove screws securing the gage
center.
to the instrument panel.
(c) Remove cover (1, fig. 4-15) and
gasket (2).
4-28
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