Check Pre-Load of Bearing
The rollers of the bearing are loaded between the
bearing cup and bearing cones in accordance with
design requirements to provide a rigid idler gear and
bearing assembly. As the bearing cones are moved
toward each other in a tapered roller bearing assembly,
the rollers will be more tightly held between the cones
and cup. In the idler gear bearings, a slight pre-load is
applied by means of a selected spacer ring between the
bearing cones, to provide rigidity of the gear and
bearing assembly when it is mounted on its hub. This
method of pre-loading is measured, in terms of pounds-
pull, by the effort required at the outer diameter of the
gear to turn the bearing cup in relation to the bearing
Any time an idler gear assembly has been removed
from an engine for servicing or inspection, while
performing engine overhaul or other repairs, the preload
should be measured as part of the operation.
The idler gear bearing must be clean and lubricated with
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.
After the idler gear, hub, and bearing are assembled
together, the bearing should be checked to ascertain
Fig. 6. Fixture for Testing Bearing Pre-Load
that the gear may be rotated on its bearing without
the pull, in pounds and ounces, required to start the gear
exceeding the maximum torque specifications, nor be so
rotating. Make several checks to obtain an average
loose as to permit the gear to be moved in relation to
reading. If the pull is within 1/2 lb. minimum to 4 lbs.
the hub by tilting, wobbling or shaking the gear.
maximum and does not fluctuate more than 2 lbs. 11
ounces, the idler gear and bearing assembly are
If the mating crankshaft and balance shaft gears are not
satisfactory for use.
already mounted on the engine, the torque required to
rotate the idler gear may be checked by mounting the
idler gear in position on the engine, using a steel plate 4
" square (pre-load test plate) against the hub and cone
as outlined below.
Mount the idler gear assembly on the engine.
Install the center bolt and washer through the gear
hub and into the cylinder block. Tighten the bolt to 8090
Place steel plate (lower plate shown in Fig. 7)
against hub and bearing. Insert three 3/8 "-16 bolts
through the plate and thread them into the hub. Tighten
the bolts to 24-40 lb-ft (34-54 Nm) torque.
Tie one end of a piece of lintless 1/8 " cord around
a 1/8 " round piece of wood (or soft metal stock). Place
the wood between the teeth of gear, then wrap the cord
around the periphery of the gear several times. Attach
Fig. 7. Plates for Bearing Test Fixture
the other end of the cord to spring scale, J 8129 (Fig.
8). Maintain a straight, steady pull on the cord and
scale, 90 ° to the axis of the hub, and note