FED-STD-791D
axis may be affected. Before installing the heater mount in the rig, the bearing's outer race
thermocouples are checked for continuity.
6.2.4 Test bearing. Before installing the test bearing on the hub, it is examined visually
for any obvious mechanical defects. If the bearing appears satisfactory, the inner race and cage
assembly is pressed onto the hub with the serial number facing the front of the rig. The
recommended fit of the bearing inner race on the hub is 0.002 to 0.0036 cm (0.0008 to 0.0014 in)
tight. After repeated usage, the O.D. of the bearing hub may become worn and result in a loose
bearing fit. When this happens, the hub may be chrome plated and reground to proper dimension
or replaced. After the bearing has been installed in the bearing head, the shaft is turned by hand
to make sure it turns freely. Bearing roughness can usually be detected in this manner. When
properly installed, the rollers should be evenly centered in the outer race. If the rollers are more
than 0.32 cm (1/8 in) off center on the outer race, check for missing shaft assembly parts or an
improperly installed bearing outer race. It is important that the lock nut on the test-bearing
retainer be tight since it imparts an axial pinch on all of the shaft assembly parts back to the load
bearing and in addition helps to prevent the bearing inner race from turning on the hub during
operation.
6.2.5 End cover. Before installing the end cover on the rig, the test-oil jet tube alignment
is verified. The jet positions midway between the outer race I.D. and the cage O.D. Alignment
is verified by assembling (outside the machine housing) the heater mount with the outer race
installed, the pinch plate, and end cover. The heater mount is fixed by installing the heater
terminal nuts and making certain that the mount O.D. coincides with the pinch plate diameter.
The end cover mounting bolts are inserted through the cover and corresponding pinch plate
holes. The test-oil jet is inserted through its holder and the jet position verified by visual
observations from the rear of the heater mount. The test- bearing roller and cage assembly is
installed in the outer race through the heater mount rear side and the jet position noted with
respect to the cage O.D. Upon subsequent assembly of the bearing machine for testing, a gasket
of Raybestos-Manhattan A-56 material, or equivalent, is installed between the end cover and
pinch plate.
6.2.6 Check of seal operation. After assembly of the bearing head, the screw thread seal
operation is checked under a 2224 N (500-pound) radial load to the load bearing by applying
351.6 kPa (51-psig) shop air pressure to the loading cylinder and hand rotating the shaft to detect
rubbing. If any rubbing occurs, the bearing head is disassembled and a slight amount of material
removed from either the screw threads or the seal plate, depending on the location and severity
of the rubbing. The material is removed from the seal plate if the rubbing is localized, and the
screw thread is ground if the rubbing is severe and occurs over a considerable area.
6.2.7 Miscellaneous joint compounds. No pipe dopes, thread compounds, or gasket
sealants are used in the assembly of the rig or test-oil system. Polytetrafluoroethylene tape, or
equivalent (no adhesive) is an effective sealant when applied to pipe threads.
6.3 Support-oil system. SAE J1966, lubricating oil is used in the support-oil system and
is not normally changed after each run. Drain periods on the support oil are governed by the
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