TM 5-3810-300-24&3
2.0 Shop Notes
located, corrected and the tester rechecked before
valve must be removed, lapped and cleaned, or
checking an injector.
replaced.
If an injector tester supply or gage line is damaged or
Occasionally dirt will get into the pump check valve in the
broken, install a new replacement line (available from the
tester, resulting in internal pump valve leakage and the
tester manufacturer). Do not shorten the old lines or the
inability to build up pressure in the tester fuel system.
volume of test oil will be altered sufficiently to give an
Pump valve leakage must be corrected before an
inaccurate valve holding pressure test. If it is suspected
injector can be properly tested.
that the lines have been altered, i.e. by shortening or
replacing with a longer line, check the accuracy of the
When the above occurs, loosen the fuel inlet connector
tester with a master injector on which the pressure
clamp and operate the tester pump handle in an attempt
holding time is known. If the pressure holding time does
to purge the dirt from the pump check valve. A few quick
not agree with that recorded for the master injector,
strokes of the pump handle will usually correct a dirt
replace the lines.
condition. Otherwise, the pump check
REFINISH LAPPING BLOCKS
blocks. The quality of the finished work depends to a
great degree on the condition of the lapping surfaces of
the 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 1 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
Fig. 2 - Refinishing Lapping Blocks
held under a strong light. The blocks are satisfactory
when the entire surface is a solid dark grey. Bright or
As the continued use of the lapping blocks will cause
exceptionally dark spots indicate defects and additional
worn or low spots to develop in their lapping surfaces,
lapping is required.
they should be refinished from time to time.
After the surfaces have been finished, remove the
It is good practice, where considerable lapping work is
powder by rinsing the lapping blocks in trichloroethylene
done, to devote some time each day to refinishing the
and scrubbing with a bristle brush.
When not in use, protect the lapping blocks against
damage and dust by storing them in a close fitting
wooden container.
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