Installation manual

TACHOMETER
TACHOMETER/HOUR METER
The tachometerlhour meter used in propulsion engine instru-
ment panels contains two separate electrical circuits with a
common ground.
One circuit operates the hour meter and the
other the tachometer. The hour
meter circuit operates on 12
volts alternator charging voltage supplied to the (+) terminal
on the back of the instrument.
The tachometer circuit operates on AC voltage 6-8 volts, fed
from one
of 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
of the two circuits in a tachometerlhour
meter.
Hour meter Inoperative
Check for the proper DC voltage between (+) and (-)
terminals.
1. Voltage present - meter is defective - repair or replace.
2. Voltage not present - trace (+) and (-) electrical con-
nections for fault. (Jump 12 volts DC to meter (+)
terminal to verify the operation.)
Tachometer Inoperative
Check for the proper AC voltage between tachometer input
terminal and (-) terminal with the engine running.
1. Voltage present - attempt adjusting meter through calibra-
tion access hole. No results, repair or replace meter.
2. AC voltage not present - check for proper alternator DC
output voltage.
3. Check for
AC voltage at tach terminal on alternator to
ground.
4. Check electrical connections from tachometer input ter-
minal 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 on the front of the crankshaft
pulley retaining nut or with a strobe-type tach, read the
front crankshaft pulley rpm at idle.
b. Adjust the tachometer with a small Phillips type screw-
driver through the calibration access hole in the rear of
the tachometer. Zero the tach and bring it to the rpm
indicated by the strobe or hand tach. (Verify the rpm at
idle and at high speed and adjust the tach as needed).
NOTE: Current model tachometers use a coarse adjustment
dial to set the tachometer to the crankshaft pulley rpms. The
calibrating screw is then used
for fine tuning.
COARSE
ADJUSTMENT
TACH INP
AC VOLTAGE
TACHOMETER CHECK (New Installation)
TERMINAL
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
in all new
installations.
1. Warm up the engine to normal operating temperature.
Remove any specks on the crankshaft pulley with a clean
cloth and place a piece
of suitable reflecting tape on the
pulley to facilitate use
of a photoelectric type tachometer.
2. Start and idle the engine.
3. Aim the light
of 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 coarse adjustment to calibrate the
instrument reading to the closest R.P.M. that the photo tach
is showing. Then use the fine calibration adjustment
to
bring the instrument to the exact reading as the photo tach.
Engines & Generators
31