b.  
Badly battered or rounded shell hexagons.

c.  
Out-of-round or damaged shielding barrel.

d.  
Chipped, cracked, or broken ceramic insulator portions.

e.  
Badly eroded electrodes worn to approximately 50 percent of original size.

2.  
Clean spark plug as required; remove carbon and foreign deposits.

3.  
Test spark plug both electrically and for resistance.

4.  
Set electrode gap at 0.017 to 0.021 inch.

INSTALLATION OF SPARK PLUGS
— CAUTION —
DO NOT INSTALL ANY SPARK PLUG THAT HAS BEEN DROPPED.

1.  Before installing spark plugs, make sure that threads within cylinder are clean and not damaged.
—CAUTION—
MAKE CERTAIN DEEP SOCKET IS PROPERLY SEATED ON SPARK PLUG HEXAGON AS DAMAGE TO PLUG WILL RESULT IF WRENCH IS COCKED TO ONE SIDE WHEN PRESSURE IS APPLIED.
2.  
Apply anti-seize compound sparingly on threads; install gasket and spark plugs. Tighten to a torque of 360 to 420 inch-pounds.

3.  
Carefully insert terminal insulator in spark plug and tighten coupling nut.

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74-20-00 Page 74-26 Issued: April 1, 1997
3I8
SWITCHING. MAGNETO AND STARTER SWITCHES. (Refer to Figure 74-24.) The magneto switches and the starter switch are located on the lower left of the instrument panel.
REMOVAL AND INSTALLATION.
Refer to Chapter 39 for removal and installation procedures.
Instrument Panel Magneto & Starter Switches (Front View)  OFF BATT MASTR OFF MAG LEFT  OFF ALTR LEFT OFF MAG RIGHT  OFF ALTR RIGHT  LEFT ALT. AMPS. 0 50 100 RIGHT ALT. AMPS. 0 50 100 OFF MAG LEFT OFF MAG RIGHT  PARK BRAKE PANEL LIGHTS 
(Rear View) 

Figure 74-24. Magneto and Starter Switches 
74-30-00 
3I9  Page 74-27 Issued: April 1, 1997 

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74-30-00 Page 74-28 Issued: April 1, 1997
3I10

CHAPTER

77

ENGINE INDICATING

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CHAPTER 77 - ENGINE INDICATING 
TABLE OF CONTENTS / EFFECTIVITY 
CHAPTER/ SECTION  SUBJECT  GRID NO.  EFFECTIVITY 

77-00-00 GENERAL 3I15
Removal and Replacement of Cluster Mounted Instruments 3I16
77-10-00 POWER 3I17
Manifold Pressure Gauge 3I17 Troubleshooting 3I17 Removal and Replacement 3I17
Electric Tachometer Installation 3I18 Removal and Installationr of Tachometer 3I18 Removal and Installation of Magnetic Sensor 3I18
77-20-00 TEMPERATURE 3I21
Cylinder Head Temperature Gauge 3I21 Troubleshooting 3I21 Removal and Replacement 3I21 Calibration 3I22
77-30-00 ANALYZERS 3I23
Exhaust Gas Temperature Gauge 3I23 Cleaning and Inspection 3I23 Troubleshooting 3I24 Removal and Replacement 3I24
Exhaust Gas Temperature Probe 3I24 Removal 3I24 Installation 3I24
77-Cont./Effec. Page 77-3 Issued: April 1, 1997
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77-Cont./Effec. Page 77-4 Issued: April 1, 1997
3I14
GENERAL.
The power plant instrumentation is designed to give an accurate and quick indication of the power conditions at which the engines are operating. Line routing for the instruments may be seen in Figure 77-1.

77-00-00 Page 77-5 Issued: April 1, 1997
CLUSTER MOUNTED INSTRUMENTS.
REMOVAL AND REPLACEMENT OF CLUSTER MOUNTED INSTRUMENTS. 
1.
Remove the four screws on the panel which will be holding the cluster to the panel.

2.
Label the wires to facilitate reinstallation.

3.
Remove the clear lens cluster cover.
4 Remove the nuts and washers from the terminals of the gauge to be replaced.

5.
Remove the gauge through the front of the cluster housing.

6.
Replace instrument in the reverse order.

7.
Check all connections for security and correctness.

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77-00-00 Page 77-6 Issued: April 1, 1997
3I16
POWER.
MANIFOLD PRESSURE GAUGE.
The manifold pressure gauge is a vapor proof, absolute pressure type instrument.  Pressure from the intake manifold of each engine is transmitted to the instrument through individual lines.  There are two in line filters which are located in the lines ahead of each instrument. They are accessible from underneath the instrument panel and should be checked for moisture and/or replaced at each 100 hour or annual inspection.  Also connected to the back of the gauge are quick drains to permit draining of any fuel or liquid that might accumulate in the lines.
TROUBLESHOOTING MANIFOLD PRESSURE GAUGE.
　
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