L
ENGINE
(2)
Fit
shim, spring and flange
to
body, and
tighten the body and retaining
nut
together
by torquing to the prescribed value.
(NOTE]
The body may be gripped in the vise,
but
not
the retaining nut. This
is
because
the nozzle might suffer distortion
if
the
nut
is
clamped between the vise jaws.
(3)
Fit
gasket and nipple
to
the body.
(4) When installing the nozzle holder assem-
blies, be sure to use new gaskets and tighten
the securing bolts to the prescribed torque
value.
(5)
Prior
to
installing the overhauled nozzle
holder assemblies, test each for "start-of-
injection" pressure, spray pattern, "after-
injection" dribbling and fuel atomization.
(a) Start-of-injection pressure test
A nozzle tester
must
be used to deter-
mine the pressure at which the nozzle
starts spraying.
If
the pressure
noted
on
the nozzle under test
is
at variance with
the specification, increase
or
decrease
the shim thickness. Changing the thick-
ness by 0.1 mm (0.04 in.) changes the
start-of-injection pressure by about
10
kg/cm
2
(142 psi).
Start-of-injection pressure
test
(b) Spray pattern test
2-42
Operate the tester lever rather slowly
to see
if
the nozzle shoots
out
fuel
intermittently. A small amount
of
fuel
is
discharged in this test at such a
pressure
as
will allow the needle valve to
chatter and, therefore, spray intermit-
tently with some low-tone sound. The
test
is
often called "chattering test." A
good spray
is
characterized by fine
atomization and straightforward jetting.
y
l,J
U
.J
1.,
~
~!
~~
,\,1
I':~
"I,'
,',I.:
.,','
Good
Bad
Bad
Spray
patterns
in
chattering
test
(c) After-injection dribbling test
See
if
the nozzle dribbles after each
injection. A dribbling nozzle must
be
replaced. In the chattering test, fuel
might ooze
out
to form a globule
of
fuel
at the nozzle tip but, since this
is
due to
the chattering action
of
the needle valve,
such a globule need
not
be taken
as
a
cause
of
nozzle replacement.
u
·····'·;·\
,l)
';'i
. ·-t
Good
i
,Iii
I
]!1
~
~
~ ~~
Bad
Bad
Dribbling in
test
condition
(d) Atomization test
Operate the tester lever rapidly, at a
rate
of
about
800 strokes per minute to
make the nozzle spray
out
with full
force. Visually observe the spray to see
if
it consists
of
uniformly fine particles
of
fuel, straight in direction and having
no fissures.
r
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