Westerbeke 20B TWO Installation Manual download pdf (Page 31)

TACHOMETER

TACHOMETER/HOUR

METER

The tachometer/hour meter used in propulsion engine

instrument panels contain two separate electrical circuits

with a common ground.

One circuit operates the hour meter

and the other the tachometer. The hour meter circuit operates

volts alternator charging voltage supplied to the ( +)

terminal on the back

the instrument.

The tachometer circuit operates

AC voltage 6-8 volts, fed

from one

the diodes in the alternator and supplied to the

tachometer input terminal while the engine is running, and

the alternator producing battery charging voltage 13.0-14.8

volts

DC.

The following are procedures to follow when

troubleshooting a fault in either

the two circuits in a

tachometer/hour meter.

Hour

meter

Inoperative

Check for the proper DC voltage between ( +) and

(-)

terminals.

Voltage present - meter is defective - repair or replace.

2. Voltage not present - trace (

+) and (-) electrical

connections for fault. (Jump 12 volts DC to meter (

tern1inal to velify the operation.)

Tachometer

Inoperative

Check for the proper AC voltage between tachometer input

tern1inal and (-) terminal with the engine running.

Voltage present - attempt adjusting meter through

calibration access hole. No results, repair

replace

meter.

2. AC voltage not present - check for proper alternator

output voltage.

3. Check for AC voltage at tach terminal on alternator to

ground.

4. Check electrical connections from tachometer input

terminal to alternator connection.

Tachometer

Sticking

1. Check for proper AC voltage between "tach inp."

terminal and (-) terminal.

2. Check for good ground connection between meter (-)

terminal and alternator.

3. Check that alternator is well grounded to engine block at

alternator pivot bolt.

Tachometer

Inaccurate

a. With a hand-held tach

the front

the crankshaft

pulley retaining nut

with a strobe-type tach, read the

front crankshaft pulley rpm at idle.

b. Adjust the tachometer using a 5/64

2mm Allen wrench

through the CAL. (calibration) access hole

the rear

the tachometer. Zero the tachometer and then adjust it to

the rpm indicated

the strobe or hand tachometer.

(Verify the rpm at idle and high rpm and adjust the

tachometer as needed)

NOTE:

Current model tachometers use a coarse adjustment

dial to set the tachometer to the crankshaft pulley rpms. The

calibrating screw

then used

for

fine tuning.

LIGHT

(+)TERMINAL

TAGH

INP

VOLTAGE

CALIBRATION

TACHOMETER

CHECK

(New

Installation)

NOTE:

In a new installation having new instrument panels,

the tachometer may not always be correctly calibrated to the

engine's

rpm

This calibration should be checked

all new

installations.

Warm up the engine to normal operating temperature.

Remove any specks

the crankshaft pulley with a clean

cloth and place a piece

suitable reflecting tape on the

pulley to facilitate use

a photoelectric type tachometer.

2. Start the engine, warm up, then set the engine speed

using the photo tach to

112

rated engine rated rpm.

3. Aim the light

the tachometer onto the reflecting tape to

confirm the engine speed. Check the instrument panel

tachometer reading. Adjust the tachometer in the panel by

using the instrument calibration pod as needed to bring

the instrument panel tachometer into the same rpm

reading as the engine.

4. Check the tachometer accuracy at idle and at rated rpm.

Adjust as needed.

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Westerbeke 20B TWO Installation Manual Page 31

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