TM 5-3895-346-14
SHOP NOTES
ENGINE OVERHAUL
flat side of the plunger does not come into full view (Fig. 3) and appears in the "advanced" or "retarded"
position, disassemble the injector and correct the rack-to-gear timing.
Figure 3. Injector Rack-to-Gear Timing
INJECTOR SPRAY TIPS
Due to a slight variation in the size of the small orifices in the end of each spray tip, the fuel output of an
injector may be varied by replacing the spray tip.
Flow gage J 25600 may be used to select a spray tip that will increase or decrease fuel injector output for a
particular injector after it has been rebuilt and tested on the calibrator.
INJECTOR PLUNGERS
The fuel output and the operating characteristics of an injector are, to a great extent, determined by the type of
plunger used. Three types of plungers are illustrated in 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
Injector plungers cannot be reworked to change the output or operating characteristics. Grinding will destroy
the hardened case and result in chipping at the helices and seizure or scoring of the plunger.
Figure 4. TYPES OF INJECTOR PLUNGERS
MASTER INJECTOR CALIBRATING KIT
Use Master Injector Calibrating Kit J 26298 to determine the accuracy of the injector calibrator.
With the test fluid temperature at 100 1(38 1 and each injector warm after several test cycles, run
F
C
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the three injectors contained in the kit. Several readings should be taken with each injector to check for accu-
racy and repeatability. If the output readings are within 2% of the values assigned to the calibrated masters,
the calibrator can be considered accurate. Injector testing can be carried out now without any adjustment of
figures. However, when testing new injectors for output, any difference between the calibrator and the masters
should be used to compute new injector calibration.
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