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
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