TRUCK SERVICE MANUAL
6. Insert PT (type D) Injector in Service Tool
12. attach fuel inlet line from ST790 or other
3375086 or ST-1058 Adapter. Fig. 6-1-36,
pressure source to injector inlet On PT (type D)
Note: ST-10585 and ST-1058-6 spacers
injectors use ST1 058 adapter.
13. Start ST790 Test Stand or other source of fuel
are not required with ST-668, for PT
and set pressure to 22 psi [152 kPa].
(type D) injectors.
14. Shift target ring in base of tool so one spray
Note: Use plunger bore plug assembly
stream hits center of No. 1 or index window.
ST-668-5012 for PT (type D) injectors.
This is tallest window and is next to target slide
7. Remove plunger assembly and spring from
This window provides +3 degrees
tolerance on injector spray stream location.
8. Select correct size plunger bore plug and rubber
On 1974 and later injector cups, +2 degrees
seal and; install in injector plunger bore. Protect
tolerance must be maintained on all streams.
injector plunger from dirt or damage during tests.
15. Each spray stream must hit a window in the
9. Install the solid knurled plug in injector drain
target ring on 1974 and later cups.
opening, Service Tool 3375086.
Note: For a cup to be acceptable no more than
10. Place injector in ST668 seat and adjust
one stream must require the increased tolerance
holddown bracket into position required, then
of the No. 1 window.
tighten thumb screw.
17. After testing, assemble plunger with spring in
11. Tighten knob against plug and seal in plunger
body adapter 'and store in clean place until ready
bore so it seals thoroughly.
for flow test.
Table 6-1-14: ST-668 Cup Seat Spacer
ST790 Injector Test Stand (Fig. 6-1-68) is used to test all
Injector Test Stand ST790
Cummins PT injectors. ST790 flow tests the complete
The ST790 Injector Test Stand is the recommended
injector assembly by measuring fuel delivery. The
injector is actuated under controlled conditions closely
Cummins injectors, but it must be properly installed and
simulating actual operating conditions. The test stand
calibrated to obtain the highest accuracy possible.
counts injection strokes, supplying fuel at a specified
pressure, thereby measuring the delivery in a glass
The ST590 Test Stand was used prior to release of
ST790 and may be converted, see your Cummins
Distributor. ST790 provides more accurate results,
better clamping arrangement and easier operation. The
accuracy and advantages of ST790 Test Stand make it
very important that ST590 Test Stands be converted;
meanwhile, your nearest Cummins Distributor can
calibrate Cummins Injectors to the latest specifications.
Test Stand Installation ST790
The ST790 must be located near hot and cold water
connections. Water temperature, controlled by a mixing
Fig. 6-1-68, F60122. Injector test stand ST-790
valve, is used to maintain test oil at an 90/95 deg. F
[32/35 deg. C] temperature range.
exceeds 95 deg. F [35 deg. C] increase cold water flow.
If temperature exceeds 135 deg. F [57 deg. C] drain and
replace with new test oil.