Ammeter; Exhaust Gas Temperature Gauge Information; Exhaust Gas Temperature Gauge Cleaning And Inspection - Piper Navajo Chieftain PA-31-350 Service Manual

NAVAJO CHIEFTAIN SERVICE MANUAL
10-77. AMMETER.
10-78. GENERAL. The ammeters are mounted in the overhead instrument panel. This instrument
measures the current flowing in the entire electrical system including the battery charging demand.
10-79. TROUBLESHOOTING. (Refer to Section XI - Electrical System.)
10-80. REMOVAL AND REPLACEMENT.
(Refer to paragraph 10-94 of this section.)
10-81. EXHAUST GAS TEMPERATURE
GAUGE.
10-82. GENERAL. This dual instrument, which is commonly referred to as EGT. is used to aid the pilot in
setting the economical fuel-air mixture for cruising flight and determining the proper fuel mixture setting at
altitudes above 5.000 ft. It is a sensing device to monitor 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
on the indicator. Attempts to LEAN the engine with a faulty E.G.T. can result in excessive C.H.T. or burned
exhaust valves.
10-83. CLEANING AND INSPECTION.
Unless mechanical damage such as broken glass. bent or broken
pointer. broken case. the following checks should be performed before removing the instrument:
a. The thermocouple probe should be removed and cleaned at each 100 hour inspection. This will
ensure good and rapid response to temperature changes. The following procedure should be used:
1. Detach the thermocouple leads from the extension lead if necessary. (Do not detach if the
probe can be removed and cleaned with leads attached.)
2.
Unscrew the attaching clamp. and with leverage applied to the CLAMP ONLY. lift out the
thermocouple assembly very carefully from the manifold. (Do not attempt to pull the thermocouple by
squeezing the spacer washers in a vice-grip pliers.)
3. Clean the probe with solvent and check for broken weld (at tip end) or burnt off end.
4. Replace the assembly carefully and retighten the clamp. If leads were disconnected. reconnect
them using a new pair of Thomas and Betts "Sta-Kon" connectors, make certain connections are tight.
b. Examine the extension lead wires for any evidence of chafing on sharp edges. This could cause
erratic fluctuation of the EGT indicator.
c. Ascertain that the connectors which mate the extension leads to the thermocouple are properly
seated. Poor contact may cause indicator fluctuation also.
CAUTIONS
I.
DO NOT cut off any excess lead wire from the thermocouples
to the indicator, at any time. This will cause the system to
be inaccurate.
2. NEVER attempt to check indicator operation or resistance
with an ohmmeter. A special bridge is required which is
accurate and will not damage the instrument.
3. DO NOT attempt to adjust the indicator. The system was
accurately calibrated at the factory.
Revised: 10/15/82
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INSTRUMENTS
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