TM 9-2320-387-24-2
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33-6.
INSPECTION
(Cont’d)
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1. Negligible damage: Minor dents, nicks, scores, cracks, and holes in body panels which are within or
are brought within reasonable limits by a simple procedure, without extensive rework, are considered
negligible damage. These defects should be considered more serious if located in main structural members
such as body side rails, A-pillars, or floor crossmembers rather than in body panels such as cowls or rear
wheelhouses. Deep wrinkles of undetermined origin in body panels should not be classed as negligible until
the source of wrinkles has been investigated and positively identified. Damage other than small dents, holes,
nicks, and scratches will require repair or replacement of the part. Refer to para. 33-8-f for repair of negligible
damage.
(a) Negligible cracks. Isolated cracks less than 0.50 in. (1.27 cm) long may be classified as negligible
cracks provided they are stop-drilled at each end to stop propagation.
(b) Negligible holes. Isolated holes no more than 0.50 in. (1.27 cm) diameter, after they are made
round with smooth edges are classified as negligible holes, provided the distance from the edge of the hole to
the nearest line of rivets exceeds the diameter of the hole.
(c) Negligible dents and distortion. Small dents and distorted areas may be classed as negligible if
they can be repaired by hammering or bending without causing the material to crack. Heat may not be used
for reforming.
2. Damage repairable by patching: Damage beyond negligible must be repaired, or the section replaced.
Patches can often be applied over damaged body panels provided damaged area is first trimmed to remove
sharp edges or notches which could cause the start of new cracks. The patch must then be sized to overlap the
area to allow for attaching rivets. Refer to para. 33.8.g for repair by patching.
3. Damage repairable by insertion: In certain cases, patch repairs may not be desirable because of
impracticality or because a flush surface is desired. In this case, damaged area must be cut away and a
partial replacement of equivalent material inserted flush with adjacent areas and backed up with a doubler.
Refer to para. 33-8.h for repair by insertion.
4. Damage necessitating replacement of parts: Parts too badly damaged for repair, or where
replacement is easier than repair, fall into this category. Repair of welded assemblies such as body mounts
are also in this category. Welded assemblies cannot be re-welded without destroying strength of the part and
must be replaced.
c. Rivet Failure. Signs of rivet failure include tipped heads, looseness, and sometimes chipped or cracked
paint. If heads are tipped in the same direction and rivets are loose in consecutive groups, the joint has
undergone excessive load. Rivet heads which are tipped in different directions, and are not in groups may be
improperly installed. With chipped or cracked paint, it may be necessary to remove paint to check true
condition of rivets. Rivets subjected to critical loads but showing no distortion should be inspected if failure is
suspected. The head should be drilled off, and the shank should be carefully punched out. Failure is indicated
by notched rivet shank and misaligned holes. Flush rivets showing head slippage within the dimple or
countersink indicate either sheet bearing or rivet shear failure and must be removed for inspection and
replacement. If failure of rivets cannot be detected by visual inspection, the joint can be checked by drilling
and punching out several rivets. If rivet shanks are notched, rivets should be replaced with next larger size
rivets. If rivet holes show elongation due to local failure in tearing of the sheet, next larger size rivet must be
used in replacement. Any deformation of the sheet around the rivet, tear-outs, or cracks between rivets
usually indicates partially failed or damaged rivets. Complete repair of the joint will require replacement by
next larger size rivets. Use the next .031 in. (0.79 mm) larger diameter rivet to obtain a tight joint when
original hole has been enlarged. If original size rivet is installed, the rivet would not be able to carry its share
of the shear load, and the joint would not meet its strength requirements.
d. Lockbolt Failure. Lockbolts are used to withstand tension loads and high-shear loads. These
fasteners are installed in their holes with an interference fit. No looseness can be permitted. Lockbolts
showing evidence of being stretched, broken, loose in their holes, or having heads that do not set flat against
the surface must be replaced. Guidelines used in 33-6.~ for detecting rivet failures also apply to lockbolts.
33-6
