remove the old grease and lubricate the bearings with
new grease. To do this. disassemble the bearing
housings and clean the inside of the housings and
housing plates or caps and the bearings with a suitable
solvent. When you have thoroughly cleansed them of
old grease. reassemble all parts except the outer plates
or caps. Apply new grease, either by hand or from a
tube, over and between the balls. The amount of grease
you should use varies with the type and frame size of
the particular motor. You should consult the
instruction sheet that accompanied the motor for this
You should add enough grease to fill the bearing
housing one-third to one-half full. Do not use more
than the amount specified. After reassembling the
motor, you should refill any V-grooves that are found
in the housing lip with grease (preferably a fibrous.
high-temperature-sealing grease) that will act as an
additional protective seal against the entrance of dirt or
The technique for greasing motors equipped with
roller bearings is quite similar to that used for ball
bearings. However, you should follow specific
instructions for the individual design because more
frequent greasing or slight changes in technique may
sometimes be necessary.
With the motor stopped, you periodically should
check the oil level in the sleeve-bearing housings. If
the motor is equipped with an oil-filler gauge, the
gauge should be approximately three-quarters full at
If the oil is dirty. drain it off by removing the drain
plug, which is usually located in the bottom or side of
the bearing housing. Then flush the bearing with clean
oil until the outcoming oil is clean.
In fractional-horsepower motors, there may be no
means of checking the oil level, as all the oil may be
held in the waste packing. In such cases, a good general
rule for normal motor service is to add 30 to 70 drops of
oil at the end of the first year and to reoil at the end of
each subsequent 1,000 hours of motor operation.
Most fractional-horsepower motors built today
require lubrication once a year. Small fan and agitator
motors often require more frequent lubrication with
3-month intervals between oilings.
Motors should be stored in a dry, clean place until
ready for installation. Heat should be supplied,
especially for larger high-voltage machines, to protect
them against alternate freezing and thawing. This
advice is equally applicable to spare coils.
Motors that have been in transit in a moist
atmosphere or have been idle for an extended period
without heat to prevent the accumulation of moisture
should be dried out thoroughly before being placed in
service. Machines also may become wet by accident.
or they may sweat as a result of a difference between
their temperature and that of the surrounding air. This
condition is harmful particularly in the case of large or
important motors, and should be prevented, by keeping
them slightly warm at all times.
You can pass current at a low voltage through the
windings, use electric heaters, or even use steam pipes
for protective purposes. During extended idle periods,
you can stretch tarpaulins over the motor and place a
small heater inside to maintain the proper temperature.
If a motor should become wet from any cause, you
should dry it out thoroughly before operating it again.
The most effective method is to pass current through
the windings, using a voltage low enough to be safe for
the winding in its moist condition.
You can apply heat externally by placing heating
units around or in the machine and cover the machine
with canvas or some other covering, and then leave a
vent at the top to permit the escape of moisture. You
can use small fans to help circulation. You should not
allow the temperature of the windings to exceed 100°C
for Class A insulated motors.
A systematic and periodic inspection of motors is
necessary to ensure best operation. Of course, some
machines are installed where conditions are ideal; and
dust, dirt, and moisture are not present to an
appreciable degree. Most motors, however, are located
where some sort of dirt accumulates in the windings,
lowering the insulation resistance and cutting down
creepage distance. Dusts are highly abrasive and
actually cut the insulation while being carried by
ventilating air. Fine cast-iron dust quickly penetrates
most insulating materials; hence, you can see why
motors should be cleaned periodically. If conditions
are extremely severe, open motors might require a
certain amount of cleaning each day. For less severe
conditions. weekly inspection and partial cleaning are