Occasionally, during an aircraft structural repair, it is wise  to examine adjacent parts to determine the true condition  of neighboring rivets. In doing so, it may be necessary to  remove the paint. The presence of chipped or cracked paint  around the heads may indicate shifted or loose rivets. Look  for tipped or loose rivet heads. If the heads are tipped or if  rivets are loose, they show up in groups of several consecutive  rivets and probably tipped in the same direction. If heads that  appear to be tipped are not in groups and are not tipped in  the same direction, tipping may have occurred during some  previous installation. The procedure for universal or protruding head rivet removal  is as follows: Inspect rivets known to have been critically loaded, but  that show no visible distortion, by drilling off the head and  carefully punching out the shank. If, upon examination, the  shank appears joggled and the holes in the sheet misaligned,  the rivet has failed in shear. In that case, try to determine  what is causing the shearing stress and take the necessary  corrective action. Flush rivets that show head slippage within  the countersink or dimple, indicating either sheet bearing  failure or rivet shear failure, must be removed for inspection  and replacement. Joggles in removed rivet shanks indicate partial shear failure.  Replace these rivets with the next larger size. Also, if the rivet  holes show elongation, replace the rivets with the next larger  size. Sheet failures such as tear-outs, cracks between rivets,  and the like usually indicate damaged rivets. The complete  repair of the joint may require replacement of the rivets with  the next larger size. The general practice of replacing a rivet with the next larger  size ( 1 ⁄ 32-inch greater diameter) is necessary to obtain the  proper joint strength of rivet and sheet when the original rivet  hole is enlarged. If the rivet in an elongated hole is replaced  by a rivet of the same size, its ability to carry its share of the  shear load is impaired and joint weakness results. When a rivet has to be replaced, remove it carefully to retain  the rivet hole’s original size and shape. If removed correctly,  the rivet does not need to be replaced with one of the next  larger size. Also, if the rivet is not removed properly, the  strength of the joint may be weakened and the replacement  of rivets made more difficult. When removing a rivet, work on the manufactured head. It  is more symmetrical about the shank than the shop head, and  there is 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.  To remove a countersunk or flush head rivet, you must: The procedure for the removal of countersunk rivets is the  same as described above except no filing is necessary. Be  careful to avoid elongation of the dimpled or the countersunk  holes. The rivet head should be drilled to approximately one- half the thickness of the top sheet. The dimple in 2117–T  rivets usually eliminates the necessity of filing and center  punching the rivet head. On thin metal or unsupported structures, support the sheet  with a bucking bar while driving out the shank. If the shank is  unusually tight after the rivet head is removed, drill the rivet  about two-thirds through the thickness of the material and then  drive the rest of it out with a drift punch.  Figure 4-98  shows  the preferred procedure for removing universal rivets. 1.  File a flat area on the head of the rivet and center punch  the flat surface for drilling. 2.  Use a drill bit one size smaller than the rivet shank to  drill out the rivet head.  3.  Drill the rivet to the depth of its head, while holding  the drill at a 90° angle. Do not drill too deeply, as the  rivet shank will then turn with the drill and tear the  surrounding metal. 4.  If the rivet head does not come loose of its own accord,  insert a drift punch into the hole and twist slightly to  either side until the head comes off. 5.  Drive the remaining rivet shank out with a drift punch  slightly smaller than the shank diameter.  NOTE: The rivet head often breaks away and climbs  the drill, which is a signal to withdraw the drill. NOTE: 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.  NOTE: On thin metal, back up the rivet on the upset  head when center punching to avoid depressing  the metal. Removal of Rivets 1.  Select a drill about 0.003-inch smaller than the rivet  shank diameter.  2.  Drill into the exact center of the rivet head to the  approximate depth of the head. 4-45