When to overhaul
The
object
of
engine overhauling
is
to
repro-
duce,
as
closely
as
possible, the vitality and
capability which the engine
had
when
it
was
new. The
symptoms
that
justify the decision
to
overhaul the engine are two: reduced
power
output
and high
consumption
of
fuel and lube
oil,
both
being
concurrent
and
attributable
to
internal deterioration inside the engine.
There
is
no
method
nor
test
that
verifies the
internal deterioration so accurately and quickly
as
compression test. With a special pressure
gauge and its
adaptor
and fittings, one can
readily measure the
"compression"
pressure on
each cylinder
of
the engine and tell, from the
readings taken,
whether
the engine should be
overhauled
or
not.
Pressure gauge,
adaptor
and
fittings
for
engine
"compression"
test
In a diesel engine, low
power
output
could
often
be due to some malconditions
in
the
injection system - damaged injection nozzles,
mistimed injection, low injection pressure, etc.
These malconditions,
if
present, call for over-
hauling
of
the injection system
components
or
for re-timing
of
the injection.
ENGiNE
Fuel injection
pump
Suppose
that
the engine has ceased
to
develop
full power, so
that
you have
to
decide
whether
the engine should be overhauled
or
not. The
right approach begins with posing these questions
to
yourself:
..
Is
fuel
or
oil
consumption
appreciably higher
than before?
..
Is
it
harder
to
start
up the engine?
..
Does the engine make more noise, coming
from inside,
than
before?
If
the answer
is
yes
to
all these questions,
read
"compression"
pressures by the
method
to be described and,
if
the readings are
too
low (as compared with the specification),
it
means
that
the engine needs overhauling
because it
is
internally deteriorated,
that
is,
its internal running parts are excessively worn
- cylinder bores, pistons, piston rings
and
valves.
If, however, the readings (compression pres-
sure) are adequately high, then the injection
system should be blamed
f01'
the low power
output.
In conducting a
"compression"
pressure test,
it
should be borne in mind
that
the pressure rise
occurring above the piston in the cylinder
is
affected by the speed with which the piston
rises on compression stroke.
It
is
for this reason
that
the specification (a certain pressure which
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