TRUCK SERVICE MANUAL
4. Screw snubber back into gauge stem.
between 370 and 390 when adjusted within
5. Place an injector into operating position In test
marked band on dial.
stand. Start the test stand. When solid fuel
begins to flow from the snubber, turn gauge
upright quickly and assemble to snubber. Let
test stand run while gauge is tightened securely
6. Assemble gauge to mounts secure with machine
screws and nuts.
7. Start test stand and observe gauge hand rise
from 0 to 120 psi [0 to 827 kPa]. It should take
approximately 2 to 3 seconds for hand to rise to
120 psi [827 kPa]. If gauge hand is slow to rise
and fall, carefully repeat Steps 1 through 6.
8. Check for gauge hand vibration, it should not
occur if copper line is properly routed and
Fig. 6-1-81, F60131. ST789 load cell
a. Tubing must be adjusted so it is neither "pulling"
or "pushing" on the gauge.
b. Tubing on the gauge must not contact any
member of test stand such as frame, motor or
gear pump cover.
c. Contact of tubing to any member of test stand
will transmit mechanical vibration into gauge and
defeat purpose of snubbers and gauge mounts.
Changing Oil And Filter
When changing oil and filters in test stand, adjust
regulator to lowest possible pressure during pump pickup
to prevent air from being forced into gauge line. If slow
gauge hand response does occur, it is an indication air
entered the system and the bleeding process Steps 1
Fig. 6-1-82, F60132. Air pressure adjustment
through 6 must be performed.
Calibrating The ST790 Test Stand
6. Remove the load test cell by returning the air
1. Before operating the test stand make sure that
valve knob to center position. With the cylinder
the cam box is filled to the top level of the sight
rod in down position, check to make sure the
glass with clean SAE 30 nonfoaming lubricating
hydraulic fluid shows in the hydraulic oil level.
7. Open the air valve. While the cylinder rod is at
2. Fill the hydraulic fluid reservoir to bulb level with
the top of its travel check to make sure there is
clean Type A automatic transmission fluid. Be
no air in hydraulic fluid sight glass. Fig. 6183.
careful not to allow oil to enter the standpipe in
8. Make sure Injector seat contains 0.020 inch [.51
the center of the reservoir.
mm] restrictor orifice when calibrating test stand.
3. The test oil tank on the stand must be kept at
least 3/4 full of Cummins 9901168 test oil or
9. Place adapter plate over master injector, ST768,
Mobil Oil Company No. MCL41.
ST1210, ST1262 or ST1306, and engage locator
4. Align timing mark (Fig. 6171) and open the
In injector mounting holes. Make sure seat is
hydraulic valve. Place the load cell, ST7905111,
retracted and timing marks are aligned at timing
in the test stand and clamp in place by opening
wheel. Fig 6171.
the air valve. Fig. 6181.
10. Position test stand link (marked NVH, NH, H)
Note: Never operate test stand with load cell in position.
over injector plunger link and place assembly in
5. Adjust air pressure by turning the knurled button
injector seat, tip back until link is below machine
on the air regulator until the load cell indicates
push rod. If necessary, adjust bracket so link is
within marked band on load cell gauge. Lock the
aligned but not rubbing.
knurled button in place with the locknut. Note
the air gauge pressure (gauge at top of Hydraulic
Reservoir). Fig. 6182. Load cell should read