TM 55-1520-240-23-1 1-14 SELF-RETAINING BOLTS INSTALLATION 1-14 WARNING Standard bolts must not be substituted for self-retaining bolts at any connection where self-retaining bolts are installed.  Loss of a bolt from any one of these flight control connections could result in the loss of the helicopter. Two types of self-retaining bolts are used.  They are positive retention bolts and impedance bolts. Both types have a fail-safe feature which prevents loss of bolt, if nut comes off.  A nut, safetied with a cotter pin, must be installed on each self-retaining bolt. Positive retention bolts have a pawl at threaded end of bolt shank.  The pawl is spring-loaded to an extended position. When extended the pawl prevents the nut from being removed.  Finger pressure compresses the pawl for removal of the nut and for removal of the bolt from the parts.  Some of the bolts contain a heat shrunk bushing which replaces the sliding bushing in the fastener build-up. This prevents installation of the bolt without the bushing being installed.  Placards are installed at each location for positive retention bolts. Impedance bolts have either spring-loaded balls, or a spring ring on the bolt shank above the threads.  These retaining elements extend beyond the diameter of the bolt and prevent it from sliding from the parts. 1. Remove positive retention bolts as follows: a. Remove cotter pin. b. Backoff nut until it is next to pawl.  Depress pawl and backoff nut from bolt. Depress pawl and remove washer. c. Pull bolt out until pawl is next to lug. Depress pawl and pull bolt out until pawl is inside lug. d. Hold parts stack-up together and pull bolt out. NOTE If stack-up separates while removing bolt, pawl may extend and catch on edge of fastener, bearing, or bushing. If pawl extends while removing bolt, use a thin piece of metal such as knife edge or rule to depress pawl.  Do not hammer bolt out. e. On bolts with integral bushings, examine the bushing for galling.  If there is galling, rework the bolt to reduce bushing diameter. 2. Rework of Positive Retention Bolts. If the bushing of a removed bolt is galled, rework it as follows: a. Measure the diameter of the bushing.  If it is greater than the diameter after rework shown in table below, reduce the diameter by machine turning or grinding.  Maintain a surface finish of  63 microinches  or less. Positive Retention Bolt Assembly Rework Diameters Bolt Assembly Part No. Bushing Diameter Before Rework Bushing Diameter After Rework 114R3650-1 0.8744 to 0.8749 0.8708 to 0.8713 114R3650-3 0.8744 or 0.8749 0.8708 to 0.8713 114R3650-6 0.6244 to 0.6249 0.6218 to 0.6223 114R3650-7 0.7806 to 0.7811 0.7774 to 0.7779 114R3650-9 0.9382 to 0.9387 0.9343 to 0.9348 114R3650-11 0.7507 to 0.7512 0.7476 to 0.7481 114R3650-16 0.6244 to 0.6249 0.6218 to 0.6223 114R3650-17 0.6244 to 0.6249 0.6218 to 0.6223 All  Dimensions  In  Inches b. If galling extends below the reduced diameter, discard the bolt. c. Inspect the reworked bolt assembly.  Use magnetic particle inspection per MIL-I-6868. Use circular magnetization thru the ends of the assembly at  800 to 100 amperes.  Use longitudinal inspection, charged coil, at  800 to 1200 amperes. 3. Install positive retention bolts as follows: a. Place countersunk washer under bolt head. Make sure countersink is next to bolt head. For helicopters (With    46  ), the positive retention bolt-bushing assembly does not have a washer under the head. CAUTION Do not apply antiseize compound on thread of bolt or nut. Change 3 1-17


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