58
condition. In addition, itcan warn
of
developing prob lems
inside the engine. If more thun a 43 psi. (300 kPa) differ-
ence exists between the highest
and
lowest read ing cylin -
ders on multicylindercngincs, the engine cannot
betuned
to develop its maximum power. Specified cyli nder pres-
sure is
390-470 psi (2700-3300 kPa).
A compression read ing that is
below the desired com-
pression pressure indicates that engine repair is required
beca use of worn or broken rings, leaky or sticking valves
or a co
mbin
ation of all.
If the
co
mpression test readings arc lower than desired.
isolate the cause by performing a wet c
ompr
ession test.
Remove the precombustion chamber (r
ef
er to Chapter
Seve
n). P
erf
orm the wet
compr
ession lest in the sameway
as the dry test.
exce
pt pour approximately
one
tablespoon
of
heavy
eng
ine oil (at least SAE 30) into the injector hole
before performing Steps
7-9.If the wet compression read-
ings are sign ificantly
higher than the dry compression
readi ngs, the cause for the low dry
comp
ression reading is
probably worn or broken rings. If there is little difference
between the read ings, the problem may be due to leaky or
sticking
valves or a faulty cylinde r head gasket. l
ft
wo ad-
ja
cent cylinders on a multicylindereng ine read Iow an
both tests, the head gasket may
be leaking between the
cylinders.
Excessively high compression readi ngs indicate carbon
buildup in the cylinder.
NOTE
A special Ope compression gauge and
adapter
is required to measure the compres-
sion
pressure in the cylin
der.
If
the neces-
sary
compression test gauge is not
available, have a diesel technician
pe
rform
the test.
I. Be sure cooling water is connected to the engine.
2. Run the engi ne until it reaches normal operating tem-
perature, then shut it
off
.
CHA PTER
THR
EE
CAUTIO.V
Be sure to remove all the inj ectors 0 11 a
mutticytinderengine
to
prevent inadvertent
starting.
3.
Remove the fuel injector(s) as described in Chapter
Se
ven.
4. Clean the injector hole.
5. Rotate the engine to b
lowout
any carbon.
6. Install the compression gauge and, if necessary, the
adapter.
7. Crank the engine at least five turns or until there is no
further increase in compression shown on the tester
gauge.
8. Record the reading. Relieve the tester pressure
valve
and remove the
co
mpression tester.
9. Repeat Steps
~-
8
for eac h remaining cy linder on
multicylinderengines.
va
lve Clea
ra
nce
Ad
ju
stm
ent
Valve clearance is the gap between the end of the valve
stem and the underside
of
the rocker
ann.
A specified
valve clearance must
bemaintained for the valves 10oper-
ate as designed. Insufficient valve clearance will cause
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