Occasionally dirt will get into the pump check valve in
If an injector tester supply or gage line is damaged or
the tester, resulting in internal pump valve leakage and
broken, install a new replacement line (available from
the inability to build up pressure in the tester fuel
the tester manufacturer). Do not shorten the old lines or
system. Pump valve leakage must be corrected before
the volume of test oil will be altered sufficiently to give
an injector can be properly tested.
an inaccurate valve holding pressure test.
When the above occurs, loosen the fuel inlet connector
If it is suspected that the lines have been altered, i.e. by
clamp and operate the tester pump handle in an attempt
shortening or replacing with a longer line, check the
to purge the dirt from the pump check valve. A few
accuracy of the tester with a master injector on which
quick strokes of the pump handle will usually correct a
the pressure holding time is known. If the pressure
dirt condition. Otherwise, the pump check valve must
holding time does not agree with that recorded for the
be removed, lapped and cleaned or replaced (J 9787).
The pump check valve must be replaced on tester J
REFINISH LAPPING BLOCKS
To refinish the blocks, spread some 600 grit lapping
powder of good quality on one of the blocks. Place
another block on top of this one and work the blocks
together as shown in Fig. 2. Alternate the blocks from
time to time. For example, assuming the blocks are
numbered 1, 2 and 3, work I and 2 together, then I and
3, and finish by working 2 and 3 together. Continue this
procedure until all of the blocks are perfectly flat and
free of imperfections.
Imperfections are evident when the blocks are clean and
held under a strong light. The blocks are satisfactory
when the entire surface is a solid dark gray. Bright or
Fig. 2 Refinishing Lapping Blocks
exceptionally dark spots indicate defects and additional
As the continued use of the lapping blocks will cause
lapping is required.
worn or low spots to develop in their lapping surfaces,
they should be refinished from time to time.
After the surfaces have been finished, remove the
powder by rinsing the lapping blocks in trichloroethylene
It is good practice, where considerable lapping work is
and scrubbing with a bristle brush.
done, to devote some time each day to refinishing the
blocks. The quality of the finished work depends to a
When not in use, protect the lapping blocks against
great degree on the condition of the lapping surfaces of
damage and dust by storing them in a close fitting
MASTER INJECTOR CALIBRATING KIT
Injector testing can be carried out now without any
Use Master Injector Calibrating Kit J 26298 to determine
adjustment of figures. However, when testing new
the accuracy of the injector calibrator.
injectors for output, any difference between the
calibrator and the masters should be used to compute
With the test fluid temperature at 100 °F ± 1 ° (38°C ± 1
°) and each injector warm after several test cycles, run
from the masters is noted, consult the calibrator
the three injectors contained in the kit. Several readings
manufacturer for possible causes.
should be taken with each injector to check for accuracy
and repeatability. If the output readings are within 2% of
The calibrated masters should only be used to qualify
the values assigned to the calibrated masters, the
calibrator can be considered accurate.