TM 5-3895-374-24-2
BELT INSTALLATION AND ADJUSTMENT
When installing new belts. do not pry the belts over
the pulley grooves. The proper method of removing and
installing new belts is to loosen the anchor screws and
the belt tightener screw, Figure 6-2, and push the motor
toward the compressor. Use the tightener screw to
adjust belt tension on new belts.
Figure 6-2. Belt Adjustments.
It is important that the belts be properly adjusted. A
belt that is too loose will slip and cause heating and
wear, and a belt that is too tight may overload the
bearings. A quick check to determine if belt adjustment
is proper may be made by observing the slack side of the
belt for a slight bow when the unit is in operation. See
Figure 6-3. If a slight bow is evident, belts are usually
adjusted satisfactorily. However, the recommended
method of checking belt tension is by the more accurate
spring scale measurement method that follows:
Figure 6-3. Visual Method.
A.
Measure the belt span (t) as shown In Figure 6-4.
B.
At the center of the span (t), apply a force
(perpendicular to the span, by attaching a spring
scale to the two outside belts The force applied to
the spring scale should be sufficient to deflect the
belts 1/64" (.396 mm) for every inch of span length
(t). For example: The deflection of 100" (2540 mm)
span would be 100/64" or 1 9/16" (39.6 mm), thus
the force applied to the spring scale should deflect
the belts to 1 9/16" (39.6 mm)
Figure 6-4. Spring Scale Method.
C. When the belts are deflected the necessary distance.
compare the spring scale reading (in lbs. force) with the
value given in the following table.
STANDARD BELT TENSION
Belt
Normal
150% Normal
Type
Tension
Tension
B
2 3/4 Ibs. (1.25 kg)
4 lbs. (1.81 kg)
C
5 1/2 lbs. (2.5 kg)
8 1/4 lbs. (3.74 kg)
If the reading is between the value for normal tension
and 150% normal tension, the belt tension should be
satisfactory. A reading below the value for normal
tension indicates the belt slack should be reduced, and
conversely, a reading exceeding the value for 150%
normal tension indicates the belt slack should be
increased. Experienced has shown that a new drive can
be tightened initially to two times normal tension to allow
for any drop in tension during run in.
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