TM 5-3810-300-24&P-3
1.7.1
GEAR TRAIN AND TIMING
Gear train noise is usually an indication of excessive
gear has only about half as many teeth as the camshaft
gear lash, scoring, pitting or excessive bearing wear.
or balance shaft gear, it turns at approximately twice the
Therefore, when noise develops in a gear train, the
speed of the crankshaft.
flywheel housing should be removed and the gear train
and its bearing inspected. A rattling noise usually
Lubrication
indicates excessive gear lash whereas a whining noise is
a result of too little gear lash.
The gear train is lubricated by overflow oil from the
camshaft and balance shaft pockets spilling into the gear
Excessive wear and scoring may result from abrasive
train compartment. A certain amount of oil also spills
substances or foreign material in the oil, introduced in
into the gear train compartment from the camshaft and
the engine by such means as removal of the rocker
balance shaft end bearings, and idler gear bearings.
cover without first cleaning away dirt.
The blower drive gear bearing is lubricated through an
external pipe lead-ing from the main cylinder block oil
The backlash between the various mating gears in the
gallery to the gear hub bearing support. The idler gear
gear train ranges from .003" to .008" with new parts and
bearing is pressure lubricated by means of oil passages
.010" with used parts.
in the idler gear hub which connect to the oil gallery in
the cylinder block.
Since the camshaft and balance shaft gears each have
the same number of teeth as the crankshaft gear, they
turn at crankshaft speed. However, as the blower drive
Checking Engine Timing
The correct relationship between the crankshaft and
check. Then, proceed as follows:
camshaft must be maintained to properly control fuel
injection and the opening and closing of the exhaust
1. Remove the valve rocker cover.
valves.
2. Select any cylinder for the timing check--it is
The crankshaft timing gear can be mounted in only one
suggested that a cylinder adjacent to one of the cylinder
position due to one attaching bolt hole being offset. The
head cover studs be chosen since the stud may be used
camshaft gear can also be mounted in only one position
for mounting a dial indicator.
as a result of the location of the keyway relative to the
cams. Therefore, when the engine is properly timed, the
3. Remove the fuel jumper lines (at the cylinder
markings on the various gears will match as shown in
selected) and install shipping caps on the injector fuel
Fig. 1.
fittings to prevent the entry of dirt. Make sure that the
valve and injector rocker arms are all in the "up" position,
An engine which is "out of time" may result in pre-
then remove-the rocker shaft bracket bolts and swing the
ignition, uneven running and a loss of power.
rocker arm assemblies back out of the way. Remove the
When an engine is suspected of being out of time, due to
injector assembly.
an improperly assembled gear train, a quick check can
be made without having to remove the flywheel and
4. Carefully place (do not drop) a rod approximately 12"
flywheel housing by following the procedure outlined
long through the injector hole and on top of the piston.
below.
5. With the throttle in the NO-FUEL position, turn the
Access to the vibration damper or crankshaft pulley, to
crankshaft slowly in the direction of rotation of the
mark the top-dead-center position of the selected piston,
engine, and stop turning when the rod.
and to the front end of the crankshaft or flywheel for
turning the engine is necessary in performing the timing
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