Service manual
Table Of Contents
5-4 Testing and adjustment
(1) Injection pressure
The pressure at which the needle valve unseats
itself against the force
of
the pressure spring is
referred
to
as
"valve opening pressure" or "begin-
ning-of-injection pressure,"
but
will be called here
"injection pressure' for short. The value 01 this
pressure
is
specified; it is checked and adjusted
as
follows:
(a) Install the injection nozzle in the nozzle tester,
and operate the manual pumping handle
of
the
tester several strokes
to
prime the nozzle.
(b)
Move
the lever
up
and down slowly, completing
each up.and-down cycle in about a second,
to
pressurize the injection nozzle, while observing
the indication
of
the test pressure gauge.
As
the
nozzle begins
to
spray, the indicating pointer
of
the gauge being deflected will start perceptively
oscillating: read the pressure right then
as
the
injection pressure.
Specifications Unit: kg/cm
2
(psi)
Item Standard
Repair
limit
Injection
120+
1
g (1706.4+
14
5.
2
)
110(1564.2)
pressure minimum
(c)
If
the reading taken
is
below the limit, increase
the thickness
of
the shim used
on
the pressure
spring. Increasing the shim thickness by 1
mm
(0.04 in.) raises the injection pressure
by
about 10 kg/cm
2
(142 psi). Adjusting shim
stock for this purpose
is
available
in
20 sizes,
from 1.0
mm
(0.0394 in.) up
to
1.95 mm
(0.0768 in.) in increments
of
0.05 mm
(0.0020
in.) each.
(2)
Spray pattern
The injection nozzles used in the present engine
are
of
throttle type. Some throttling action takes
place when the needle
valve
begins
to
unseat,
thereby limiting the amount
of
fuel being sprayed
out
during the initial stage
of
each fuel injection.
Thus, each slug
of
fuel sprayed
out
may be
regarded
as
consisting
of
two parts: initial throttled
spray and tenninating main spray.
When tested
on
the nozzle tester, the injection
nozzle
can
be made
to
produce these two kinds
of
spray for visual inspection. Initial throttled spray
comes about when
the
tester lever
is
operated at
a rate
of
60
cycles per minute (up and down
'in
one second); terminating main spray occurs when
the lever is operated rapidly at a rate of, say, 4
to
6 cycles per second.
-62-
1
2
3
lllJ
lUI
II!lI
1\
1-Good
4·After-dribble
2-5pray
cone
too
large 5·Fissured spray
3-Off-i:enter spray 6-Whirling spray
Possible patterns
of
spray