Cummins/Onan NTA-855 Generator Set

⚠ Do not break or remove the lockwire.

⚠ Do not use the ST-1224 if stop crank adjustment is required.

Tools: ST-1224 Tachometer drive adapter (2:1 ratio), tachometer, 1/16 inch hex allen wrench

1. Remove the tachometer drive adapter.
2. Install the ST-1224 in place of the standard drive adapter; connect the tachometer and overspeed stop switch to the ST-1224.
3. Start the engine and warm to operating temperature.
4. Set the engine speed to the appropriate overspeed switch set speed in Table 1-3 as indicated by the tachometer.
5. Remove the round head dust cover screw marked 2 from the top of the switch.
6. Insert a 1/16 inch hex allen wrench into the adjusting screw located just below the surface of the cover.
7. Turn the adjusting screw counterclockwise to lower the engine shut off speed; clockwise to raise it.
8. Replace the dust cover screw.
9. Reset the switch by pushing the reset button on top of the switch.
10. Replace the ST-1224 with the original drive adapter and reconnect the cables.

Tools: Frequency meter or tachometer

1. Idle Speed potentiometer: turn counterclockwise 20 turns, then clockwise 10 turns (mid position).
2. Run Speed potentiometer: turn counterclockwise 20 turns, then clockwise 10 turns (mid position).
3. Gain potentiometer: turn screw fully counterclockwise.
4. Droop potentiometer: fully counterclockwise for isochronous, approx. 40 for 3 percent droop, approx. 80 for 5 percent droop.

Tools: Frequency meter or tachometer

1. Close main line circuit breaker and apply approximately 1/4 of rated load.
2. Make sure engine speed is constant.
3. Turn Gain potentiometer clockwise slowly until engine speed is not constant.
4. Slowly turn potentiometer counterclockwise until constant speed is achieved.
5. Turn potentiometer counterclockwise an additional 1/2 division.

⚠ Use only proper engine barring techniques; do not attempt to rotate the engine by pulling or prying on the fan.

Tools: Snap-On Model TQ12B or equivalent in-lb torque wrench, screwdriver adapter, ST-669 Adapter

1. Turn the crankshaft in direction of rotation until the No. 1 'VS' mark appears; verify both intake and exhaust valves are closed for cylinder No. 1.
2. Tighten the injector hold-down capscrew to 30 to 35 ft-lbs [41 to 47 N·m].
3. Turn the adjusting screw down until the plunger contacts the cup and advance an additional 15 degrees to squeeze the oil from the cup.
4. Loosen the adjusting screw one turn; tighten with an in-lb torque wrench and screwdriver adapter to the cold-setting value.
5. Hold the adjusting screw and tighten the locknut to the specified torque.
6. Turn the crankshaft to the next 'VS' mark per firing order and repeat.

⚠ Be sure the injector and valve set markings are in proper alignment with the indicator mark.

Tools: feeler gauge

1. Loosen the locknut and back off the adjusting screw.
2. Insert a feeler gauge between the rocker lever and the top of the crosshead.
3. Turn the screw down until the lever just touches the gauge.
4. Lock the adjusting screw in this position with the locknut and torque to specification.

⚠ Do not adjust any other voltage regulator potentiometers or rheostats; they are factory-calibrated.

Tools: Screwdriver

1. Loosen voltage control rheostat locking nut; turn rheostat fully counterclockwise, fully clockwise, then to mid position.
2. Remove cover from voltage regulator housing on engine side of generator conduit box.
3. With set operating and voltage monitored, adjust Coarse Voltage Potentiometer to desired generator voltage.
4. Perform fine voltage adjustment (+3 percent) with control rheostat and retighten locking nut.
5. Stop and restart generator set to confirm proper operation.
6. If voltage cannot be brought within range, check wiring per unit wiring diagram and repeat; contact service representative.
7. Shut down set and replace voltage regulator housing cover before returning to service.

Tools: dial indicator, feeler gauge, long capscrew

1. Remove the exhaust and intake piping from the turbocharger to expose the ends of the rotor assembly.
2. Remove one capscrew from the front plate and replace it with a long capscrew; attach an indicator and register the point on the end of the rotor shaft.
3. Push the shaft from end-to-end and note the total indicator reading.
4. Check the radial clearance on the compressor wheel only by pushing the wheel toward the side of the bore and using a feeler gauge between the wheel vane tips and the bore.
5. If end clearances exceed the limits, remove the turbocharger and replace it with a new or rebuilt unit.
6. Install the exhaust and intake piping to the turbocharger.

⚠ Concentrations in excess of limits can cause sludge to form in the water filter.

Tools: Fleetguard DCA Coolant Checking Kit Part No. 3300846-8 or Cummins 3375208

1. Dilute one part engine coolant with nine parts tap water; mix well.
2. Fill vial to scribe mark with diluted coolant; add two or three drops nitrite indicator solution and swirl to uniform red.
3. Add nitrite test solution 'A' one drop at a time, mixing between drops, until color changes from red to pale blue, gray or green.
4. Record number of drops and consult Table 2-2 for coolant condition and maintenance required.

⚠ Parts originally supplied must not be deviated from without qualifying agency approval (Underwriters Laboratory / Factory Mutual Research).

1. Contact operating personnel responsible for the fire protection system and obtain approval.
2. Close all cooling system drains.
3. Remove the heat exchanger cap; check or fill engine coolant supply; open the water filter inlet and outlet valves.
4. Prelubricate the engine with API Class CD or CC oil, SAE 15W40 or 20W40; on turbocharged engines add 2 to 3 oz. [60 cc] oil to the turbocharger oil inlet line.
5. Check the crankcase oil level and fill to the high mark on the dipstick.
6. Remove the fuel pump solenoid wire and crank the engine through two cranking cycles using the fire pump controller.
7. Turn the governor idle adjusting screw counterclockwise 6 turns to permit near idle speed at initial start-up.
8. Verify the lube oil system is under pressure.
9. Operate the engine for 8-10 minutes and look for leaks, unusual noises or other indications of improper operation.
10. Set the overspeed stop switch.
11. Stop the engine and check the engine oil and expansion tank coolant levels; top off if necessary; clean the raw water strainer.
12. Start the engine and bring it to the fire pump required operating speed; adjust the raw water pressure regulator and readjust speed if necessary.
13. Lock the governor lever (naturally aspirated) or max speed screw (turbocharged) in position.
14. Shut off the engine; notify operating personnel and obtain authorized signature of acceptance.

⚠ Mechanical tightening will distort or crack the filter head.

1. Close the shut-off valves on the inlet and drain lines.
2. Unscrew the element and discard.
3. Apply a light even coat of lubricating oil to the gasket sealing surface prior to installing the filter.
4. Install a new element and tighten until the seal touches the filter head, then an additional one-half to three-fourths turn.
5. Open the shut-off valves.

⚠ Mechanical tightening will distort or crack filter head.

1. Close shut-off valves on inlet and drain lines.
2. Unscrew element and discard.
3. Install new element, tighten until seal touches filter head, then an additional one-half to three-fourths turn.
4. Open shut-off valves.

⚠ Never operate the engine with the oil level below the 'L' (low) mark or above the 'H' (high) mark.

1. Bring engine to operating temperature, shut down the engine, remove the drain plug from the bottom oil pan and drain the oil.
2. Install the drain plug and torque per engine model.
3. Fill the crankcase to the 'H' (high level) mark on the dipstick.
4. Start the engine and visually check for oil leaks.
5. Shut down the engine; allow 15 minutes for oil to drain back into the pan; recheck the oil level and add oil as required.