Cessna 172 Maintenance Manual page 33

(d) NAS1738, NAS1939 and some NAS9301 through NAS9311 blind rivets also have oversize
shanks.
Replacement shall not be made with rivets of lower strength material.
B.
C. Hi-Shear Rivets.
(1) When Hi-Shear rivets are not available, replacement of sizes 3/16 inch or greater rivets shall be
made with bolts of equal or greater strength than the rivet being replaced, and with self-locking
nuts of the same diameter. It is permissible to replace Hi-Shear rivets with Hi-Lok bolts of the
same material, diameter and grip length.
D. Blind Rivets.
(1) Blind rivets have higher deflection rates in shear than standard solid rivets, are more susceptible
to fatigue failure and are not as strong as solid rivets in thin sheets. For this reason, it is not
advisable to replace any considerable number of solid rivets in a given joint by blind rivets,
because this may result in overstressing the remaining solid rivets. The hollow blind rivet shall
not be used. The blind rivet shall be of the same or greater strength than the rivet it replaces. In
cases of dimpled assemblies (the process of forming the metal around a hole to form a conical
indentation to receive the tapered head of a flush rivet or a screw), the rivet holes shall be
drilled after the sheets are dimpled. When possible, the exposed end of each clipped plug
shall be coated with epoxy primer. Blind rivets shall not be used in fuel bay areas except in
cases of absolute necessity, and must be sealed. If blind fasteners other than blind rivets are
encountered, it is recommended that replacements be made with identical fasteners.
E. For a list of approved solid shank and Hi-Shear rivet substitutions, refer to Tables 1 and 2.
5. Rivet Diameters
A. Rivet diameters range from 3/32 inch to 3/8 inch. Sizes of 1/8 inch, 5/32 inch, and 3/16 inch are
most frequently used. Since smaller diameter rivets lack proper structural qualities and larger
diameter rivets dangerously reduce the splice or patch area, extreme care should be exercised
before substituting other than the specified sizes of rivet diameter.
6. Rivet Lengths
A. Proper length of rivets is an important part of a repair. Should too long a rivet be used, the formed
head will be too large, or the rivet may bend or be forced between the sheets being riveted. Should
too short a rivet be used, the formed head will be too small or the riveted material will be damaged.
If proper length rivets are not available, longer rivets may be cut off to equal the proper length (not
grip). Rivet length is based on the grip.
7. Solid Shank Rivets
A. Removal of Solid Shank Rivets (Refer to Figure 1).
(1) When it becomes necessary to replace a rivet, extreme care should be taken in its removal so
that the rivet hole will retain its original size and replacement with a larger size rivet will not be
necessary. If the rivet is not removed properly, the strength of the joint may be weakened and
the replacement of rivets made more difficult.
(2) When removing a rivet, work on the manufactured head. It is more symmetrical about the shank
than the shop head, and there will be less chance of damaging the rivet hole or the material
around it. To remove rivets, use hand tools, a power drill or a combination of both. The preferred
method is to drill through the rivet head and drive out the remainder of the rivet with a drift punch.
First, file a flat area on the head of any round or brazier head rivet, and center punch the flat
surface for drilling. On thin metal, back up the rivet on the shop head when center punching
to avoid depressing the metal. The dimple in 2117-T3 rivets usually eliminates the necessity of
filing and center punching the rivet.
(3) Select a drill one size smaller than the rivet shank and drill out the rivet head. When using a
power drill, set the drill on the rivet and rotate the chuck several revolutions by hand before
turning on the power. This procedure helps the drill cut a good starting spot and eliminates the
chance of the drill slipping off and tracking across the metal. While holding the drill at a 90°
angle, drill the rivet to the depth of its head. Be careful not to drill too deep because the rivet
CESSNA AIRCRAFT COMPANY
SINGLE ENGINE
STRUCTURAL REPAIR MANUAL
© Cessna Aircraft Company
51-40-00
Page 2
Jun 1/2005