REMOVAL AND REPLACEMENT OF MANIFOLD PRESSURE GAUGE.
Refer to Chapter 39 and Removal of Face Mounted Instruments.
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ELECTRIC TACHOMETER INSTALLATION. (Refer to Figure 77-2.)
The tachometer is dual needle electrical instrument which indicates engine revolutions per minute (RPM) by use of a magnetic sensor attached to the left magneto on each engine. The tachometer indicates engine performance from 500 to 3000 RPM. The electrical schematic can be found in Chapter 91.
REMOVAL AND INSTALLATION OF TACHOMETER.
The tachometer is located on the pilot’s side of the instrument panel below the dual manifold pressure gauge.
1.
Disconnect the harness from the back of the instrument.
2.
With the instrument supported, remove the four retaining screws, and withdraw the unit from the airplane.
3.
The unit can be reinstalled in the reverse order.
REMOVAL AND INSTALLATION OF MAGNETIC SENSOR.
1.
Access the left rear area of the engine.
2.
Locate the magnetic sensor on the right side of the left magneto. Trace the sensor wiring harness to the quick connector and disconnect.
3.
Unscrew the magnetic sensor from the magneto housing.
4.
For installation, reverse the above procedure.
CHART 7702. TROUBLESHOOTING ELECTRIC TACHOMETER
Symptom Probable Cause Remedy
Both pointers inoperative Circuit breaker tripped Reset circuit breaker
One pointer inoperative Defective magnetic sensor Replace magnetic sensor
One pointer inaccurate Defective instrument Replace tachometer
— CAUTION —
ADJUSTMENT AND REPAIR OF THE TACHOMETER IS ONLY AUTHORIZED BY QUALIFIED INSTRUMENT REPAIR FACILITES.
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TACHOMETER CALIBRATION DATA
RPM PULSES / SECOND TOLERANCE (RPM)
500 1000 1500 2000 2500 2600 3000 8.33 16.67 25 33.33 41.67 43 50 ±25.0 ±25.0 ±25.0 ±25.0 ±25.0 ±25.0 ±40.0
Figure 77-2. Electric Tachometer Installation
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TEMPERATURE.
CYLINDER HEAD TEMPERATURE GAUGE.
The cylinder head temperature gauges are in their respective instrument clusters, located on the instrument panel. These instruments measure cylinder head temperature using a sender located in a cylinder head in each engine. The cylinder head used is determined by the engine manufacturer. This gauge is an electrical instrument and is wired thru the instruments circuit breaker.
— Note —
Each cylinder head gauge needle should be centered + 1/2 a needle width on the dot with electrical power off. With 14 VDC applied to the system the gauge should indicate approximately the known temperature. On a cold engine there should be a drop of the needle.
TROUBLESHOOTING CYLINDER HEAD TEMPERATURE GAUGE.
CHART 7703. CYLINDER HEAD TEMPERATURE (TROUBLESHOOTING)
Trouble Cause Remedy
Instrument shows no indication. Engine is cold. Power supply wire open. Defective sender. Defective instrument. Open circuit breaker. Warm up engine. Repair wire. Replace sender. Replace instrument. Troubleshoot for fault.
Instrument goes all the way to upper stop. Wire grounded between sender and gauge. Defective sender. Repair wire. Replace sender.
REMOVAL AND REPLACEMENT.
Refer to the General section of this chapter under Removal of Cluster Mounted Instruments.
77-20-00 Page 77-11 Issued: April 1, 1997
CYLINDER HEAD TEMPERATURE GAUGE CALIBRATION.
A calibration chart has been included for use in verifing that the suspected faulty gauge is within tolerance. Actual recalibration of the gauge must be performed by the manufacturer or an approved instrument repair facility.
1.
With the instrument installed in the aircraft, the aircrafts’ power connected (14 VDC) and the ground connected.
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