Appearance Description Cause Solution
Chunk‑out
Pieces or chunks of rubber
material have broken off the belt.
When chunk‑out has occurred, a
belt can fail at any moment.
Chunk‑out can happen when
several cracks in one area move
parallel to the cord line. Heat, age,
and stress are the primary
contributors.
Replace the belt
immediately.
Uneven rib wear
Belt shows damage to the side
with the possibility of breaks in
the tensile cord or jagged edged
ribs.
A foreign object in the pulley can
cause uneven wear and cut into the
belt.
Replace the belt and
inspect all pulleys for
foreign objects or damage.
Cracking
Small visible cracks along the
length of a rib or ribs.
Continuous exposure to high
temperatures, the stress of bending
around the pulley leads to cracking.
Cracks begin on the ribs and grow
into the cord line. If three or more
cracks appear in a three‑inch
section of a belt, eighty percent of
the life is gone.
Replace the belt
immediately.
NOTE: Minor, transverse cracks (across the belt width) may be acceptable. Longitudinal cracks (in the direction of belt length)
that join transverse cracks are NOT acceptable.
Checking
Inspect the drive belt for:
• Proper belt tension deflection
• Excessive wear
• Cracks
• Fraying
• Glazed surfaces
• Proper tension
Use moderate thumb pressure on the belt at the location with the longest distance between two pulleys.
Description
Deflection 13 mm (1/2 in.)
NOTE: Minor, transverse cracks (across the belt width) may be acceptable. Longitudinal cracks (in the direction of belt length)
that join transverse cracks are not acceptable.
Section 4 - Maintenance
90-8M0128973 eng MAY 2017 Page 71
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