(e)
Install probe in engine.
500
Jan 20/83 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 77-21-21 Page 603
EXHAUST GAS TEMPERATURE THERMOCOUPLE PROBE - CLEANING/PAINTING
1. Exhaust Gas Temperature Thermocouple Probe Cleaning
A. General
(1) Since operating temperatures to which EGT thermocouple probes are subjected are high, carbon deposits and dirt accumulation normally experienced at cooler locations will not present a cleaning problem. Perform any minor cleaning operations which may be necessary, exercising caution to prevent mechanical damage.
NOTE: Carbon coating on thermocouple probe head reduces thermocouple resistance. Before checking resistance value, remove this coating, by using piston engine spark plug cleaning equipment containing AC Cleaning Compound, Type 2. Care shall be taken not to subject parts to excessive grit blasting.
CAUTION: INSULATION MATERIAL USED WITHIN THERMOCOUPLE PROBE WILL READILY ABSORB LIQUIDS. SINCE OPERATION OF THERMOCOUPLE MAY BE ADVERSELY AFFECTED BY PRESENCE OF LIQUIDS IN INSULATION, IT IS IMPORTANT THAT LIQUID SOLVENTS NOT BE USED IN ANY WAY WHICH WOULD PERMIT THEIR ENTRY INTO SHIELD.
B. Clean Thermocouple Internally
(1)
Insert small nozzle into probe exhaust holes and remove carbon around thermocouple leads by air blasting.
(2)
Direct air blast at approximately 100 psig through nozzle.
(3)
Suggested nozzle may be fabricated from stainless steel tubing in accordance with dimensions shown in figure 701.
NOTE: Carbon removal will aid in increasing insulation resistance of thermocouple.
C. Clean Thermocouple by Grit Blasting
(1) Carbon deposits which sometimes form on the head and terminals reduce thermocouple resistance. This coating may be removed by inserting the head only (not the probe) into a standard spark plug cleaning unit containing AC Cleaning Compound, Type 2.
CAUTION: SUBJECT THE THERMOCOUPLE PROBE HEAD TO BLASTING ONLY LONG ENOUGH TO REMOVE THE CARBON COATING FROM TERMINALS AND FROM THE AREA AROUND THEIR BASES.
500
Nov 15/67 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 77-21-21 Page 701
Thermocouple Probe Cleaner 500
77-21-21 Figure 701 Nov 15/67
Page 702
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
EXHAUST GAS TEMPERATURE HARNESS AND LEAD - REMOVAL/INSTALLATION
1. Remove EGT Harness and Leads
A. Obtain access to EGT circuit connector by opening left cowl panel. EGT circuit connector is located approximately, at the 7 o'clock position on fan exhaust outer case.
NOTE: Some engines have junction boxes in place of connectors.
B. Disconnect EGT circuit connector. On engine equipped with a junction box, remove output leads.
C. Remove four nuts and screws securing connector receptacle or junction box to bracket.
D. Remove two bolts securing EGT harness fitting to fan exhaust outer case.
E. Check that thrust reverser is in forward thrust position to permit entrance into engine exhaust section.
F. Observe the following precautions for maintenance in engine exhaust section.
(1)
Pull applicable engine ignition circuit breaker on circuit breaker panel P6, and placard the circuit breaker with DO NOT CLOSE.
(2)
Placard thrust reverser controls with DO NOT OPERATE.
WARNING: SERIOUS INJURY CAN OCCUR IF ENGINE IS STARTED AND/OR IF THRUST REVERSER IS OPERATED.
G. Enter engine exhaust section.
H. Remove 12 screws retaining fan exhaust inner rear case. Slide it to rear. Refer to Fan Discharge Section, Chapter 72.
I. Disconnect alumel and chromel leads from thermocouple probes.
CAUTION: DO NOT BEND OR TWIST THERMOCOUPLE PROBE TERMINALS, AS TERMINALS MAY LOOSEN IN SUPPORTING INSULATION, AND THERMOCOUPLE FUSED JUNCTION MAY BREAK.
J. Remove 15 screws securing EGT harness to turbine rear inner case.
Nov 15/69 77-21-31 Page 401 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
K. Pull receptacle or junction box through fan exhaust outer case, and remove harness through rear of engine.
CAUTION: IN ALL HANDLING AND STORAGE, EGT HARNESS AND LEADS SHOULD BE HUNG ON RACK OR LAID ON CLEAN TABLE FREE OF OIL AND MATERIAL WITH WHICH IT MAY BECOME ENTANGLED. SEVERE REPEATED FLEXING AND HARD BENDING OR TWISTING WILL BREAK OR FRAY EXPOSED INSULATION. IF HUNG ON A RACK, CARE MUST BE TAKEN NOT TO INTRODUCE ANY SMALL RADIUS BENDS IN ANY PART OF ASSEMBLY. IT IS DESIRABLE TO HANG EGT HARNESS AND LEADS ON A RACK WHICH IS SIMILAR TO A SEGMENT OF A CIRCLE HAVING APPROXIMATELY THE SAME DIAMETER AS THE ENGINE CASINGS.
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