Operating Principle
Nozzle operation is as follows:
1. High pressure fuel from theinjection pump enters
the fuel inlet stud and flows down drilled
passages in the body of nozzle holder, Figure
13.
2. Fuel enters fuel duct and pressure chamber of
nozzle assembly. When fuel pressure overcomes
preset pressure of the adjusting spring, the pintle
is forced upward off its seat and a fine mist of fuel
is injected into the pre-combustion chamber
where
it
atomizes and mixes with the hot com-
pressed air.
3.
If compression temperatures are high enough,
the fuel-air mixture ignites. Injection continues
until the spill port clears the top of the metering
sleeve in the injection pump and dumps the high
pressure fuel into the sump allowing the pressure
spring to close the injector and cut off fuel
injection to the cylinder.
Do
not disturb the injector pressureadjusting
screw; it cannot be reset without proper
equipment.
Excess fuel is returned to the tankafter each injection
cycle by a return line from the nozzle.
A
fuel return
fitting combines the return fuel from the injectors with
the flow-through fuel from the injection pump bleed
valve.
A
return line connected at this point returns the
combined fuel back to the fuel supply tank.
Nozzle Spray Pattern
If one cylinder
is
misfiring, its nozzle may be
operating improperly. Faulty nozzles can be checked
by loosening the high pressure line from theinjection
pump to each nozzle (one at a time).
If streamers are visible, the pattern
is
badly distorted
or
the
nozzle drips before
it
reaches opening
pressure,
it
is defective and must be cleaned or
replaced.
Cleaning is the most important part
of
nozzle maintenance. Make
sure the work area and equipment are exceptionally clean.
A
second method for determining a misfiring nozzle is
to remove the exhaust manifold and run the engine
under load. One can readily see by theexhaust which
cylinder is not operating properly.
Adjustment:
To
adjust the opening pressure, remove
each nozzle from the engine and remove the cap nut
over the adjusting screw of each. Install the nozzle to
be tested on astaticfuel nozzletesting fixture (may be
purchased from Onan). Following the instructions on
the tester, adjust the opening pressure to 1750 psi
(12.075 kPa) by turning the adjusting screw.
Clockwise increases the pressure and
counterclockwise decreases
it.
Do
not try to adjust
the pressure without a testing fixture.
Disassembly:
When removing and disassembling
nozzles, separate and label all components of each
nozzle. Never interchange components between
nozzles.
1. Remove each nozzle assembly from engine and
remove fuel inlet and return lines.
2. Clamp nozzle holder body in a vise and remove
nozzle cap nut and nozzle.
3.
Install nozzle cap nut loosely to protect lapped
surface for the holder body.
4.
If
necessary to further disassemble nozzle,
reverse pressure adjusting screw and lift out
spring and spindle assembly.
Do
not attempt to disassemble the nozzles or
adjust nozzle pressure without the propertest
equipment. A nozzle pressure tester is essential to do a satisfactory
job.
A
suspected nozzle can be checked in the field by
removing it from theengineand reconnecting itto the
high pressure line. The spray pattern (Figure 14) can
be observed as the engine is cranked.
71
Keep hands away fromaspraying nozzle! The
nozzle
discharge
pressure
can
penetrate the
skin and may cause blood poisoning or a serious skin infection.
The Cleaning procedure (Figure
15)
is extremely important when
disassembling injection equipment. Always rinse in clean fuel
before reassembling.
Injection Nozzle Tester
Testing and adjustment can be performed only with a
nozzle tester, Figure
16.
Do
not attempt to disassem-
ble the nozzles or adjust nozzle pressure without the
POOR
proper test equipment.
-
SPRAY PATTERN
:
..I
?!
.
,
Opening pressure, leakage and spray pattern can be
checked using the tester. If any of the above malfunc-
tions appear (except opening pressure), the nozzle
valve and seat can be inspected with a magnifying
glass for erosion, scoring, etc. If cleaning with solvent
does not correct the malfunctions, a new nozzle tip
will be required. Theopening pressure can then beset
and spray pattern checked.
-*.."
,:;.
.@''C
.697
h.
FIGURE
14.
NOZZLE SPRAY PATTERN
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