(3) New bearings with insufficient clearance.
can be loosened by tapping a flat cold
chisel in the crack between the cap and
(4) Grit or foreign substances working into the
the motor frame, first on one side and
bearing.
then the other. Care should be taken to
(5) Motor nose clamped.
see that the cap is properly supported by
(6) Excessive end play in truck axles.
a helper or backed up by blocking when it
b. In case of trouble, investigate at once the level
is being loosened in order to prevent its
of oil in the well and make sure that it is up to the
dropping suddenly and causing personal
amount specified under OIL LEVEL, in the general data,
injury. The lower half of the axle bearing
will drop down with the cap and can be
sure that it has not fallen away from the shaft; if it is not
readily knocked out with a wooden block
in proper shape, repack in accordance with instructions
and hammer. To remove the upper half
under lubrication, paragraph 39.
of the bearing, jack up under the motor
c. In the case of new axle bearings, it is well to
frame a sufficient amount to relieve the
examine the clearance as bearings too tightly set up are
weight on the bearing then revolve the
frequently the cause of trouble. If the trouble persists
upper half around the axle until it can be
with the bearing freshly packed, oil at the right level, and
slipped off below. If the bearing sticks in
ample clearances, remove the bearing and examine. If
the frame it can be knocked loose by
the bearing shows signs of cutting, carefully scrape
driving down on the flange with a hammer
down to a new surface, or if too badly scored, replace
and wooden block.
with a new bearing.
b. When new bearings are installed, insert shims
d. Before replacing a bearing, which has been
0.014 inch thick between the axle cap and the motor
cutting, examine the journal carefully. Remove any
frame. Drive the axle caps in straight, as rocking will
roughness with fine emery paper, taking care after the
distort the splines and pinch the bearings.
The
operation to remove all traces of grit with a clean rag,
minimum radial clearance between the axle and the
and rub over the journal with oil. Do not use grease on
bearing should be 0.010 inch. The assembly shims
a journal which is lubricated by oil and waste, as the
need not be removed unless the bearing shells become
grease will glaze over the waste surface and prevent the
loose in service and it is necessary to restore the
oil from reaching the bearing.
clamping action between bearing seats and the axle
bearings. At such a time it is desirable to either use
83. Brushholder and Brushes
thinner assembly shims, or no shims, as may be
a. The brushbolder and brushes can be inspected
dictated by the crush which may be necessary to control
bearing clearances without bearing-shell distortion.
by removing the commutator cover.
Under no
circumstances should a carbon brush be permitted to
c. See that a new bearing is perfectly clean and
wear down so far that the brushholder finger bears on
rub a little oil over the surface before putting it in place.
the carbon box. Replace any brush which may wear to
d. Repack with clean new waste and fill oil well to
such an extent, that the finger will be less than one-
the proper level. Refer to paragraphs 37 through 44.
eighth of an inch at the end of its travel before the next
The straps holding the motor nose should not be applied
inspection.
in such a manner that they produce a clamping action
b. Brush thickness is very important and the
as severe stresses in the nose and axle bearings may
clearance of a new brush in the holder should be
result. At least an inch clearance on each side of the
approximately 0.004 to 0.010 of an inch; if the clearance
nose is necessary to allow for the wear of truck parts.
is much less than the minimum, the carbon will tend to
stick in the box, and if greater than 0.025 of an inch the
82. Hot Axle Bearings
brush may rattle, wear away its sides and chip or break.
a. Hot bearings will occur occasionally and are
The width of a brush is not so important as it nay have
usually the result of one of the following causes:
as much as 1/16 inch clearance in the box without
(1) Lack of oil in bearings.
causing any trouble.
(2)Imperfectly packed bearings.
39
