DETROIT DIESEL 53
SHOP NOTES-TROUBLE SHOOTING-SPECIFICATIONS-SERVICE TOOLS
CHECKING INJECTOR TESTER J 9787
The injector tester J 9787 should be checked monthly to be sure that it is operating properly. The following
check can be made very quickly using test block J 9787-49.
Fill the supply tank in -the injector tester with clean injector test oil J 8130. Open the valve in the fuel supply
line. Place the test block on the injector locating plate and secure the block in place with the fuel inlet
connector clamp. Operate the pump handle until all of the air is out of the test block; then clamp the fuel outlet
connector onto the test block. Break the connection at the gage and operate the pump handle until all of the air
bubbles in the fuel system disappear. Tighten the connection at the gage. Operate the pump handle to
pressurize the tester fuel system to 2400-2500 psi. Close the valve on the fuel supply line. After a slight initial
drop in pressure, the pressure should remain steady. This indicates that the injector tester is operating
properly. Open the fuel valve and remove the test block.
If there is a leak in the tester fuel system, it will be indicated by a drop in pressure. The leak must be located,
corrected and the tester rechecked before checking an injector.
Occasionally dirt will get into the pump check valve in the tester, resulting in internal pump' valve leakage and
the inability to build up pressure in the tester fuel system. Pump valve leakage must be corrected before an
injector can be properly tested.
When the above occurs, loosen the fuel inlet connector clamp and operate the tester pump handle in an
attempt to purge the dirt from the pump check valve. A few quick strokes of the pump handle will usually
correct a dirt condition. Otherwise, the pump check valve must be removed, lapped and cleaned, or replaced.
If an injector tester supply or gage line is damaged or broken, install a new replacement line (available from the
tester manufacturer). Do not shorten the old lines or the volume of test oil will be altered sufficiently to give an
inaccurate valve holding pressure test.
If it is suspected that the lines have been altered, i.e. by shortening or replacing with a longer line, check the
accuracy of the tester with a master injector on which the pressure holding time is known. If the pressure
holding time does not agree with that recorded for the master injector, replace the lines.
REFINISH LAPPING BLOCKS
As the continued use of the lapping blocks will cause worn
or low spots to develop in their lapping surfaces, they
should be refinished from time to time. It is a good
practice, where considerable lapping work is done. to
devote some time each day to refinishing the 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. 1. 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.
Fig. 1 Refinishing Lapping Blocks
Imperfections are evident when the blocks are clean and
held under a strong light. The blocks are
August, 1972 SEC 2.0