Section XIII. MAINTENANCE OF CONTROLS AND INSTRUMENTS

Section XIII. MAINTENANCE OF CONTROLS AND INSTRUMNETS

4-42. Description

a. The engine controls and instruments are mounted on the control panel which is part of the dash assembly of the

engine. Refer to figure 1-3 for the wiring diagram showing the electrical connections between the engine and controls.

The function of the controls and instruments is described in table 2-1.

b. The engine has three protective devices which will shut down the engine under certain conditions which could

damage the engine. These conditions are high coolant temperature, low oil pressure, and engine overspeed. In each of

these emergency conditions, the engine shutdown is accomplished by grounding the primary of the magneto to prevent

the engine ignition system from operating. The adjustment and replacement of these devices are the responsibility of

direct support maintenance.

c. Two large gages on the engine control panel indicate the suction and discharge pressures of their related

systems. They are connected to the pump by hoses and fittings, and each system incorporates a valve to disconnect the

gage from the system if desired. A dampener in the system at each gage prevents momentary pressure surges from

damaging the related gage.

d. The tachometer-hourmeter mounted on the control panel is driven by a flexible drive shaft which connects to a

drive adapter on the overspeed governor arm. The drive adapter meshes with a threaded portion of the overspeed

governor drive shaft, providing the rotational force necessary to operate the tachometer and hourmeter.

e. The starter disengage relay, mounted on the control panel, opens the circuit to the starter solenoid switch to

deenergize the start circuit immediately when the engine starts, and prevents the operation of the starter at any time

while the engine is running. This protects the engine starter from damage which could be caused by accidental operating

of the starter pushbutton while the engine is running. The operating coil of the relay is connected to alternator output so

that the start circuit is held open whenever there is alternator output.

4-43. Control Panel Engine Controls and Instruments

a. Removal and Disassembly.

Caution: Disconnect the battery cable (6, fig. 4-1) from the positive battery terminal (4) before

disconnecting any leads to the engine controls and instruments. This will prevent shorts which could damage

the alternator, voltage regulator, and other parts.

(1) Disconnect the electrical leads from the engine controls and instruments on the control panel. Tag leads to

facilitate reassembly.

(2) Remove and disassemble the engine controls and instruments from the control panel as shown in figure 4-

36.

b. Cleaning and Inspection.

(1) Clean all parts by wiping them with a cloth dampened lightly with cleaning solvent (fed.

spec. - -680); take care to prevent the solvent from entering the interior of the components.

(2) Inspect all meters and gages for cracked dial glass, defaced or illegible dial marking, sticking or binding

dial pointers, damaged terminals, evidence of entry of moisture, and other damage. Replace damaged gages and

meters.

(3) Check all switches for cracked cases, difficult operation, lack of positive switch action, and other damage.

Check the switches for continuity, using a multimeter or test lamp. Replace defective switches.

(4) Inspect the starter disengage relay for cracks, dented housing, loose or damaged terminals, and other

damage. Apply 24 volts across the coil terminals and check for continuity across the contact terminals. No continuity

should exist. Disconnect the 24-volt input to the coil terminals.

There should not be continuity across the contact terminals. Replace a damaged or inoperative relay.

c. Reassembly and Installation.

(1) Reassemble and install the controls and indicators on the control panel as shown in figure 4-36.

(2) Connect the electrical leads to the components as shown in figure 1-3.

4-44. Tachometer and Tachometer Drive a. Removal.

(1) Disconnect the tachometer shaft (1, fig.4-37) from both the tachometer-hourmeter (2) and from the

tachometer drive (3) on the overspeed governor drive mechanism.

(2) Remove the tachometer form the control panel.

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