Specifications

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Haly-Yearly Maintenance : 1) Clean windings of motors subjected to corrosive or other elements,
also bake and varnish them, if necessary. 2) In the case of slip-ring motors, check slip-rings for
grooving or unusual wear. 3) Check grease in ball and roller bearings and make it up where
necessary taking care to avoid overfilling. 4) Drain all oil bearings, wash with petrol to which a
few drops of oil have been added, flush with lubricating oil and refill with clean oil.
Annual Maintenance
1. Check all high speed bearings and renew, if necessary.
2. Blow out all motor windings thoroughly with clean dry air. Make sure that the pressure
is not so high as to damage the insulation.
3. Clean and varnish dirty and oily windings.
4. Overhaul motors which have been subjected to severe operating conditions.
5. Renew switch and fuse contacts if damaged.
6. Check oil for its dielectric strength.
7. Renew oil in starters subjected to damp or corrosive elements.
8. Check insulation resistance to earth and between phases of motor windings, control
gear and wiring.
9. Check resistance of earth connections.
10. Check air gaps.
11. Check condition of all fasteners.
The normal value of air gap: it’s measurement
Air gap depends upon the size of the motor. A.C. motors have much smaller air gap than
D.C. motors. The gap between the rotor and the stator varies from a 0.35 mm to few mm
(few mils to 50 mils) or more depending upon the size of the motor. The air gap is measured by
inserting long steel feeler-gauge leaves in the air gap between the rotor and the stator. The
maximum thickness of the feeler that can be passed is the value of air gap. At least four readings
should be taken at different points around the periphery of the motor, i.e. top, bottom, front and
back. When any new motor is installed, air gap readings should be clearly recorded in the motor
history sheet and filed for future reference. Later on, if the top air gap is found to be much higher
than at the sides and the bottom, it clearly shows that the bearings have worn down. Belt-driven
machines usually show greater wear on one side than on the other. Several manufactures of
motors provide suitable holes in the end covers so that a feeler-gauge may be inserted for
measuring the air gap.
15.4 Removing a Bearing
It is important to take great care during the bearing removal to ensure that the bearing, shaft
and housing are not damaged. Bearing removal is best accomplished by using a bearing puller
for standard outer and inner rings. When removing bearings that have a backing shoulder that
extends beyond the cone large rib, a puller that pulls through the rollers should be used. it is
recommended to use a three–arm puller rather than a two–arm one as the three–arm puller is
more stable. Whenever possible, apply the withdrawal force to the ring with the interference fit.
The inner rings of cylindrical roller bearings generally have a tight interference fit, which requires
high forces to remove. In such cases, using a puller can cause damage to the shaft and ring,