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
~ne
of
the
diodes
in
the
alternator
and
supplied
to
the
tachometer input
terminal
while
the
engine
is
mnning,
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
(-)
tenninals.
1.
Voltage
present - meter
is
defective - repair or replace.
2.
Voltage
not
present - trace (+)
and
(-)
e1ectlical
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 mnning.
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
ca"
With a hand-held tach on
the
frollt of the crankshaft
pulley retaining nut or with a strobe-type tach,
read
the
front crankshaft pulley rpm at idle.
b. Adjust the tachometer using a
5/64
or 2mm Allen wrench
through the
CAL.
(calibration) access hole in
the
rear of
the
tachometer. Zero
the
tachometer
arid
then adjust it
to
the
rpm indicated by
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
is
then
usedior
fine
tuning.
COARSE
ADJUSTMENT
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
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
instmment 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
rt:ading
as
the
photo
tach,
4.
Set
the
tachometer
to
the
idle
speed
(the
engine idle
speed
has
been
factory
adjusted
and
the
idle
screws
and
high
speed
screws
have
been locked
in
place).
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--------------------------
Engines &
Generators
24
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