TM 5-3810-300-24&P-3
Shop Notes 2.0
If it is suspected that a fuel injector is "out of time",
the injector rack-to-gear timing may be checked
without disassembling the injector.
A hole located in the injector body, on the side
opposite the identification tag, may be used to visually
determine whether or not the injector rack and gear
are correctly timed. When the rack is all the way in
(full-fuel position), the flat side of the plunger will be
visible in the hole, indicating that the injector is "in
time". If the flat side of the plunger does not come
into full view (Fig. 3) and appears in the "advanced"
Fig. 3 - Injector Rack-to-Gear Timing
or "retarded" position, disassemble the injector and
correct the rack-to-gear timing.
INJECTOR SPRAY TIPS
Due to a slight variation in the size of the small orifices in
Flow gage J 21085 may be used to select a spray tip that
the end of each spray tip, the fuel output of an injector
will increase or decrease fuel injector output for a
may be varied by replacing the spray tip.
particular injector after it has been rebuilt and tested on
EFFECT OF PRE-IGNITION ON FUEL INJECTOR
Pre-ignition is due to ignition of fuel or lubricating oil in
Before replacing the injectors, check the engine for the
the combustion chamber before the normal injection
cause of pre-ignition to avoid recurrence of the problem.
period. The piston compresses the burning mixture to
Check for oil pull-over from the oil bath air cleaner,
excessive temperatures and pressures and may
damaged blower housing gasket, defective blower oil
eventually cause burning of the injector spray tip and
seals, high crankcase pressure, plugged air box drains,
lead to failure of the injectors in other cylinders. When
ineffective oil control rings or dilution of the lubricating oil.
pre-ignition occurs, remove all of the injectors and check
for burned spray tips or enlarged spray tip orifices.
INJECTOR PLUNGERS
The fuel output and the operating characteristics of an
output or operating characteristics. Grinding will destroy
injector are, to a great extent, determined by the type of
the hardened case and result in chipping at the helices
plunger used. Three types of plungers are illustrated in
and seizure or scoring of the plunger.
Fig. 4. The beginning of the injection period is controlled
by the upper helix angle. The lower helix angle retards
or advances the end of the injection period. Therefore, it
is imperative that the correct plunger is installed
whenever an injector is overhauled.
If injectors with different type plungers (and spray tips)
are mixed in an engine, erratic operation will result and
may cause serious damage to the engine or to the
equipment which it powers.
Fig. 4 - Types of Injector Plungers
Injector plungers cannot be reworked to change the
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