AUXILIARY POWER SYSTEM COMPONENTS INSPECTION continued
Grease may vent through the vent port under certain conditions such as overfilling or operating under
high ambient temperatures. Under these conditions, wipe grease away from housing and continue to
use power take-off assembly. Oil stains or wetness appearing on the covered port at the bottom of the
PTO clutch housing is acceptable. If oil is leaking from the covered port, the clutch shall be replaced if
the leakage rate exceeds 1 drop per minute with APU running.
h. Check APU power take-off clutch for external oil or grease leaks, heat discoloration, and cracks.
(1) Fluorescent-penetrant inspect if cracks are suspected (TM 55-1500-335-23).
External oil leakage is most likely to be at covered port. Do not confuse grease at this location with
grease coming from duplex vent. Grease from duplex vent will migrate to the covered port area.
External grease leakage is most likely to be at forward lip seal and duplex vent. Heat discoloration is
usually confined to duplex bearing housing area.
(2) Grease discharge from covered port. None allowed.
(3) Oil discharge from covered port shall not exceed 1 drop per minute with APU running.
i. Check APU power take-off clutch for internal oil or grease leaks, heat blackening, and friction disk
Friction disk has four uniformly spaced radial grooves cut into its surface. Measurements must be
taken in area between grooves.
(2) Wetness from duplex vent port and covered port is acceptable.
j. Check APU fuel control quill shaft for cracks, damaged splines, and other damage. None allowed.
k. Check APU fuel solenoid valve for damage.
(1) Check for gap between the coil assembly and valve body. None allowed.
(2) Check for yielded or deformed cover assembly, especially near screw heads. None allowed.
l. Check APU combustor liner for distortion.
(1) Distortion greater than 0.125 INCH is not allowed.
m. Check APU combustor liner for cracks.
(1) Cracks connecting any holes, separated by less than 0.250 INCH of material, greater than 0.125 INCH, or
located to threaten material breakaway not allowed.
n. Check APU combustor liner for thinning.
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