Planet ES-10024B-1 Maintenance Manual page 39

Aircraft Alternator
Maintenance Manual
3.4 Continued
D. If an alternator is determined to be at fault, note that HET sells alternators with or without
a pulley due to the desire of engine and airframe manufacturers to sometimes use their
own custom pulley and belt arrangements. The HET alternator designated ES10024B-1
is delivered without a pulley. Other HET ES10024B series alternators are delivered
with varied size and type pulleys.
E. Unusual belt condition, low belt tension, belt contamination, and belt vibration are other
sources of belt noise. A screech or squeal that occurs when starting or increasing
engine RPM rapidly typically indicates a lack of tension so check belt tension. A tapping or
grinding sound caused by debris imbedded in the drive side of the belt can be the cause
and should be checked. Grinding noise can result from worn or damaged bearings
which must be replaced (overhaul or replace alternator). This will eliminate the
bearing noise and possible damage to the alternator. Mechanical noise from vibration
can develop over time as drive components such as pulleys and spring tensioners (if
used) wear beyond tolerance, as bearings wear, or as belts wear and stretch allowing
brackets and attachments to loosen.
F. Specific belt noises may give clues to misalignment conditions. Noises can occur in both
single V type and Poly-V type belts. The belt is less likely to generate misalignment noise
when in new condition. As a belt wears, it will develop a smooth, glossy surface which
will increase the possibility of noise. A wear condition will be accelerated if misalignment
exists between any of the pulleys in the drive system.
G. A drive misalignment will make a "Chirp" noise in both the common V belt and the flat
Poly-V belt. This is caused by entry of the belt contact surface into the pulley as the
V(s) seat into the pulley groove there sill be a chirp that is not repeated as the belt exits.
The angle between belt surface and pulley is the critical factor responsible for causing
the "chirp" from a misalignment. Misalignment angle can result from many different
combinations of pulley positions. An in or out "positioning" error and/or an angular "tilting"
error are two typical examples.
H. Misalignment noise is most likely to occur on the shortest span in a drive system, such as
between two adjacent accessory pulleys. Proper pulley alignment is particularly critical
in these locations. The common V belt pulley has a generally large groove while the
nearly flat multi-groove pulley has very small grooves guiding the belt both can have
considerable misalignment and create the same noises .
I. Misalignment noise is generally loudest at idle speed and diminishes with increasing
engine rpm, often vanishing higher RPM's. The presence of high humidity (or a wet belt)
often increases the likelihood for misalignment noise to occur.
ES1031
Rev. A: 11 Aug. 2021
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24-30-01
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