TM 5-3810-300-24&P-3
IDLER GEAR AND BEARING ASSEMBLY 1.7.4
Fig. 3 - Idler Gear Details and Relative Location of Parts
selected spacer ring between the bearing cones, to
permit the gear to be moved in relation to the hub by
provide rigidity of the gear and bearing assembly when it
tilting, wobbling or shaking the gear.
is mounted on its hub. This method of pre-loading is
If the mating crankshaft and camshaft or balance shaft
measured, in terms of "pounds-pull", by the effort
gears (depending upon engine model) are not already
required at the outer diameter of the gear to turn the
mounted on the engine, the torque required to rotate the
bearing cup in relation to the bearing cones.
idler gear may be checked by mounting the idler gear in
Any time an idler gear assembly has been removed from
position on the engine, using a steel plate 4" square and
an engine for servicing or inspection, while performing
3/8" thick against the hub and cone as outlined below.
engine overhaul or other repairs, the pre-load should be
measured as part of the operation.
However, if the gears are on the engine, a suitable
fixture, which may be held in a vise, may be made as
After the idler gear, hub, and bearing are assembled
shown in Fig. 5. Three plates, a "-13 x 2 " bolt and a
together, the bearing should be checked to ascertain that
plain washer are used with a "-13 nut and plain washer
the gear may be rotated on its bearing without exceeding
for mounting. One of the plates is used to take the place
the maximum torque specifications, nor be so loose as to
of the flywheel housing, and the other two plates, the
cylinder block.
"Engine-mounted" conditions are
simulated by tightening the nut to 80-90 lb-ft torque and
tightening the three plate-to-hub attaching bolts to 25-40
lb-ft torque. The components of the fixture may be made
from steel stock in accordance with the dimensions
shown in Fig. 6.
The idler gear bearing must be clean and lubricated with
clean light engine oil prior to the pre-load test. Idler gear
assemblies which include new bearings should be
"worked in" by grasping the gear firmly by hand and
rotating the gear back and forth several times.
Fig. 4. Pressing Hub into Bearing
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