3.
If the gauge does not meet the tolerances set forth in the chart, it must be replaced or recalibrated.
4.
Reinstallation should be the reverse of the procedure used to disconnect it.
— Note —
To facilitate installation, mark or label all wires prior to removal.
77-20-00 Page 77-12 Issued: April 1, 1997
3I22
ANALYZERS.
EXHAUST GAS TEMPERATURE GAUGE.
This dual instrument, which is commonly referred to as EGT, is used to aid the pilot in setting the most economical fuel-air mixture for cruising flight at a power setting of 75% or less. It is a sensing device which monitors the temperature of exhaust gases leaving the engine cylinders. If it is found defective after checking with the troubleshooting chart, it should be replaced. If the leads to the gauge are defective in any way, they must be replaced. When replacing leads, it is necessary to use the same type and length of wire, because the resistance of the leads is critical for the proper operation of this gauge. When troubleshooting this instrument be certain the system being checked coincides with the system selected on the indicator.
CLEANING AND INSPECTION.
Unless mechanical damage is evident such as broken glass, bent or broken pointer, or broken case, the following checks should be performed before removing the instrument:
1.
Remove probe from exhaust stack and check for broken weld (at tip end) or burnt off end. Measured resistance of probe should be .8 ohms. Clean the connections with steel wool before reassembly.
2.
Disconnect lead wires at instrument and measure length and diameter. Resistance with lead wires connected to probe should be 3.3 ohms. Clean connections with steel wool before reassembly.
3.
With leads connected to instrument, heat probe with propane torch to dull red. The meter should read up to the fourth graduation or approximately 1500° F. Before making this check, make sure that the adjustment screw, which is located in the rear of the instrument case, is in the center of its travel. If this screw has been turned to either end of full travel, it will shut the instrument off and no indication will be shown on the pointer. If meter still does not read, replace it.
— CAUTION —
DO NOT CONNECT OHMMETER ACROSS METER. IT WILL BURN OUT THE MOVEMENT OF THE METER.
TROUBLESHOOTING EXHAUST GAS TEMPERATURE GAUGE.
CHART 7704. EXHAUST GAS TEMPERATURE (TROUBLESHOOTING)
Trouble Cause Remedy
Gauge inoperative. Master Switch OFF. Circuit Breaker OUT. Defective gauge, probe or wiring. Adjusting potentiometer turned off scale. Turn switch ON. Push breaker IN. Check probe and lead wires for chafing, breaks or shorting between wires and/or metal structure. Reset potentiometer.
Fluctuating reading. Loose, frayed or broken electrical leads or faulty connections. Clean and tighten connections. Repair or replace defective leads.
77-30-00 Page 77-13 Issued: April 1, 1997
REMOVAL AND REPLACEMENT OF GAUGE. (Refer to Figure 77-1.)
1.
Disconnect and label the wires from the EGT gauge at the instrument panel.
2.
Remove the four screws securing the instrument to the panel.
3.
Install the gauge by reattaching the cables to their appropriate terminals.
EXHAUST GAS TEMPERATURE PROBE.
REMOVAL OF EGT PROBE.
1.
Disconnect the lead cable from the rear of the instrument and remove it through the aircraft to the engine.
2.
Cut the safety wire at the probe clamp and remove the probe from the number one cylinder exhaust.
INSTALLATION OF EGT PROBE.
— Note —
When installing the probe, make sure to leave a minimum of 0.5 inch slack between where the lead cable attaches to the engine and engine mount, to accommodate engine shock movement.
1.
If not already done, drill a 0.129 inch hole for the probe in the number one cylinder exhaust manifold at 45°(typical) to the centerline of the cylinder, and 4.5 inches down from the mounting flange of the manifold.
2.
Install the probe in the hole drilled for it, and torque the worm screw clamp to 45 inch-pounds.
3.
Cut off any excess of the clamp over 0.75 inch and file corners smooth.
— CAUTION —
WHEN COILING THE LEAD CABLE, DO NOT LET IT BEND PAST A
0.125 INCH RADIUS.
4.
Run the cable back across the engine and mount, through the leading edge of the wing (where extra cable should be coiled and tied to an existing bundle), and into the fuselage to the rear of the instrument.
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