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 TM 55-1905-221-14-3
6-23.1.
GEAR TRAIN AND ENGINE TIMING (Continued).
Balance weights, one fastened to the inner face of each gear (camshaft and balance shaft) are important in
maintaining perfect engine balance. These are in addition to the weights cast integral with the gears.
Gear train noise is usually an indication of excessive gear lash, scoring, pitting or excessive bearing wear.
Therefore, when noise develops in a gear train, the flywheel housing should be removed and the gear train and its
bearings inspected. A rattling noise usually indicates excessive gear lash whereas a whining noise is a result of too little
gear lash.
Excessive wear and scoring may result from abrasive substances or foreign material in the oil, introduced in the
engine by such means as removal of the rocker cover without first cleaning away the dirt.
The backlash between the various mating gears in the helix steel gear train ranges from .003" to .008" with new
parts.
Since the camshaft and balance shaft gears each have the same number of teeth as the crankshaft gear, they will
turn at crankshaft speed. However, as the blower drive gear has only about half as many teeth as the camshaft or
balance shaft gear, it turns at approximately twice the speed of the crankshaft.
b. Lubrication.
The gear train is lubricated by overflow oil from the camshaft and balance shaft pockets spilling into the gear train
compartment. A certain amount of oil also spills into the gear train compartment from the camshaft and balance shaft
end bearings, and idler gear bearings. The blower drive gear bearing is lubricated through an external pipe leading from
the main cylinder block oil gallery to the gear hub bearing support. The idler gear bearing is pressure lubricated by oil
passages in the idler gear hub which connect to the oil gallery in the cylinder block.
c. Engine Timing.
The correct relationship between the crankshaft and camshaft must be maintained to properly control fuel injection
and the opening and closing of the exhaust valves.
The crankshaft timing gear can be mounted in only one position due to one attaching bolt hole being offset. The
camshaft gear can also be mounted in only one position as a result of the location of the keyway relative to the cams.
Therefore, when the engine is properly timed, the markings on the various gears will match as shown below.
6-316
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