CAB BODY REPAIR (CONT)
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.
Negligible Dents And Distortion. Small dents and distroted areas may be classified as negligible
if they can be repaired by hammering or bending without causing the material to crack. Heat
may not be used for reforming.
Damage Repairable By Patching. Damage beyond negligible must be repaired or the section replaced.
patches can often be applied over damaged body panels. damaged area must first be trimmed to
remove sharp edges or notches which could cause start of new cracks. Patch must then be sized to
overlap the area to allow for attaching rivets. refer to repair by patching, below.
Darnage 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 repair by insertion, below.
Damage Necessitating Replacement Of Parts. Parts are too badly darnaged for repair, or replacement
is easier than repair; repair for welded assemblies such as body mounts. welded assemblies cannot be
rewelded without destroying their strength and must be replaced.
Signs of rivet failure include tipped heads, looseness, and 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 misalined 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 rivet, tear outs, or cracks between rivets usually indicates partially
failed or damaged rivets. Complete repair of the joint will require replacement by the next larger size rivets.
Use the next 1/32-in. larger diameter rivet to obtain a tight joint when original hole has been enlarged. If
original size rivet is installed, rivet would not be able to carry its share of shear load, and the joint would
not meet its strength requirements.
Lock Bolt Failure
Lock bolts are used to withstand tension loads and high-shear loads. These fasteners are installed in
holes with an interference fit. No looseness can be permitted. Lock bolts showing evidence of being
stretched, broken, loose in holes, or having heads that do not set flat against the surface must be replaced.
Guidelines used in Rivet Failure, above, for detecting rivet failures also apply to lock bolts.