10-56. BODY REPAIR
Sealing compound (Appendix C, Item 59)
This task covers:
The body is constructed from aluminum alloys that have been heat-treated to obtain high strength.
Welding cannot be used to make body repairs. Heat generated in welding will reverse the heat
treatment process and cause a great reduction in strength of material.
Solid 3/16-in. diameter aluminum rivets are the primary method of joining body components. Rivets
are inserted into a hole through two pieces of metal, and a second head is formed by manual or
pneumatic impact or by squeezing the rivet. A bucking bar is used to back up the rivet to form rivet
head. When making repairs, use blind rivets of the same size or oversize diameter with the
appropriate grip length.
Blind structural aluminum rivets of 3/16-in. diameter are used in applications where there is access
from only one side of the part. Blind rivets are installed using a tool that pulls on the rivet stem,
causing a bulbed head to form on the back side of the part. Fastening is complete when stem breaks
off. High strength is obtained in blind structural rivets by mechanically locking the remaining stem
inside rivet body. Blind pop rivets are used in locations where nonstructural attachments such as
latches, striker plates, etc., are attached to the body.
Steel pull-type lockbolt fasteners in 3/16 and 1/4-in. diameter are used where tension or high shear
loads exist. Lockbolts are two-piece unthreaded fasteners. One part is a high-strength, steel-
headed, bolt-like part with serrations on its shank. The mating part is a collar which is swaged
over the serrations, causing the fastener to be locked in place.
Rivnut/plusnut fasteners are tubular rivets with internal threads. Rivnut/plusnut fasteners are
installed using a tool that engages the threads of the fastener and extends a pull, causing the
shank to expand tightly against the material being fastened. This process is called upsetting a
5.1. Struxnut fasteners are round, steel, with internal threads. Struxnut fasteners are installed using
an automated or manual ramming device.
To facilitate repairs to body, it is acceptable to replace lockbolts and rivets with 1/4-in. AN4 series
bolts. Do not replace lockbolts with rivets. Standard threaded fasteners should not be used, as these
will quickly wear the aluminum structure. Bolt lengths should be chosen so that the cylindrical
portion of bolt is bearing on all members being joined. Bolts are designated as AN4-XX or AN4C-XX
where XX defines grip length. Tighten all bolts to 70-75 lb-in. (8-9 Nm).
Fatigue strength of riveted joints and seams is increased by one part epoxy adhesive. This adhesive
requires special material storage and metal preparation along with a low-temperature heat cycle
for curing. Because of its impracticality in field repairs, epoxy adhesive will not be used. Where
possible, extra rivets and thicker metal gauges should be used instead of adhesives. When making
repairs, note epoxy exists and that parts may be difficult to separate, even after rivets are removed.
General mechanics tool kit:
automotive (Appendix B, Item 1)
Tool kit, riveter (Appendix B, Item 123)