Garmin GFC 600H Maintenance Manual page 60

For the Pitch and Roll Servos, the desired friction between the arm and the hub is set in the following
procedure (Refer to Figure 4-1 when performing these instructions):
NOTE
The P/N 117-01080-( ) output arm has a ¼" square hole as well as 1.125" flats, both of which can
be used to couple with a torque wrench. The square hole is offset from the axis of rotation. Torque
wrench drive should be perpendicular to the servo output arm to ensure accurate torque
measurement, regardless if either the square hole or the flats with a crowfoot attachment are used.
Use the torque wrench adapter calculation per AC 43.13-1B Figure 7-2 to compensate for the
measurement if the torque wrench drive is not perpendicular to the arm.
1. Hand-tighten castellated nut until seated against the Belleville washers.
2. Lock the servo output shaft with the Shaft Locking Device (Garmin P/N 117-01307-00) or hold
the output hub in place using an open ended wrench.
3. Alternate the arm a minimum of 30 degrees clockwise and counter-clockwise three times in each
direction. A socket wrench may be inserted into the square drive hole on the arm to help provide
leverage to move the armature. This action provides initial wear on friction washers and is
necessary before the final friction is set.
4. Torque the castellated nut to 30 in-lbf as an initial setting (with calibrated torque wrench). From
this point forward, regular ¾" socket can be used to tighten the nut.
5. Set the torque wrench to 40 in-lbf. Friction measurements are taken by placing the torque wrench
drive into the square hole in the servo output arm. Use a ¼" extension bar, if desired. Ensure the
wrench drive is perpendicular to servo output arm and the output arm movement is not restricted
by the wrench drive wedged against the Shaft Locking Device.
6. Apply clockwise (CW) torque to the servo output arm. Ensure the torque wrench drive is square to
the arm.
7. Gradually increase the torque on the castellated nut until the torque wrench indicates the friction to
be greater than or equal to 40 in-lbf.
NOTE
Friction increases by approximately 50 in-lbf for every castle nut rotation (or 1 in-lbf per
every 0.001" of nut displacement).
8. Adjust torque on the castellated nut until the measured torque on the servo output arm is between
40 and 44 in-lbf. The servo output arm frictional torque is considered within range if the output
arm slips at maximum specified torque but does not slip at minimum specified torque.
9. Switch the torque wrench direction and repeat steps 6 through 8 while applying the torque counter-
clockwise (CCW). Ensure the castellated nut is aligned with the hole in servo shaft to allow for
cotter pin installation before making any final adjustments.
10. The measured servo output arm torque is the average of the values obtained from rotating the arm
in both directions. The torque is in range if the computed average is between 40 and 44 in-lbf.
11. Align the output hub and armature as shown in Figure 4-2 and install the shear fuse. Garmin
P/N 117-01307-00 shaft locking device (optional) or an open ended wrench can be used to help
align arm with the hub.
12. Install a new cotter pin in accordance with MS33540 (NASM 33540) Safety Wiring and Cotter
Pinning.
13. Remove shaft locking device (if used) and install the servo in accordance with the aircraft
installation drawing, if it was removed.
190-02081-03
Rev. 3
GFC 600H HFCS Part 27 STC Maintenance Manual
Page 4-11