FINDING THE PROBLEM IN CASE OF POOR
ENGINE PERFORMANCE
If
test
specifications
cannot be met:
1.
Check, by
excluding
one
cylinder
at a time,
that the compression pressure drop
is
cons·
tant
in order
to
ascertain the functional
effi·
ciency and
uniformity
of
nozzles
or
try
once
again using a set
of
calibrated
test
nozzles.
2. Look
for
the causes
of
poor engine perfor·
mance. Use a compression·
tester
applying
it
in succession
to
each cylinder,
to
which
the
present
test
data and procedure refer. (See
chart.)
Test the engine when temperature has reached
158 °F. (70 °C.), corresponding
almost
to
the
limit
of
the
white
band
of
the panel-mounted
temperature gauge, and
stop
the engine.
1.
Remove the
injectors
from the cylinders.
2.
Install a
compression
tester in place
of
the
injector
corresponding
to
the
cylinder
to
be
tested.
3.
Hold the
injection
pump
in
"STOP"
position
and take the readings,
turning
the engine
with
the starter motor.
The pressure reading for a normally operating
engine, recorded at temperature
of
about 180
oF
(82 °C.) and at sea level (760 mm.
of
mercury), and
for
a speed
of
about 650
RPM
is
375-425
PSI
(26.4-29.9 k/cm
2
)
with
all
injectors
removed.
The
minimum
permissible pressure reading
for
a
worn engine
is
375
PSI
(26.4 k/cm
2
).
It
must
be kept in mind that pressure
drops
of
1%
for
every 100 m. increments
of
altitude. (Ap·
proximately
320 feet.)
The maximum permissible pressure
difference
between the various cylinders is 50
PSI
(3.5
k/cm
2
).
Compression faults can be traced to: valves and
seats,
pistons
and
their
rings,
cylinder
head
gasket.
60402
FIG. A.0/3 CHECKING ENGINE COMPRESSOR
WITH TESTER
A CAUTION!
Pressure
test
data are reliable
only
if
the gauge
is
functionally
efficient
and
correctly
installed
and
if
temperature and speed requirements have
been met. Do
not
start overhauling
or
repairing
an
engine
following
a
single
low
compression
reading,
or
if
the gauge
is
not
the
one
indicated
or
if
the
test
has
not
been carried on as
specified.
Engine·
5
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