Cummins/Onan 4BT 3.9 Generator Set

⚠ To avoid engine or timing pin damage, disengage the timing pin after locating top dead center.

Tools: 1/2-inch drive, Engine Barring Tool, Part No. 3824591, Feeler Gauge, 14-mm Wrench, Flat-Blade Screwdriver or 5-mm Allen Wrench, 15 mm wrench

1. Remove the valve cover.
2. Locate top dead center (TDC) for cylinder No. 1 by barring the crankshaft while pressing on the timing pin.
3. When the timing pin engages the hole in the camshaft gear, cylinder No. 1 is at TDC on the compression stroke.
4. Set only valves indicated by the arrows (E = exhaust, I = intake).
5. Holding the locknut steady with the wrench, adjust the valve clearance with the screwdriver or Allen wrench.
6. Tighten the locknut to 24 N*m [18 ft-lb], and measure the valve lash again.
7. Mark the vibration damper, and rotate the crankshaft 360 degrees.
8. Adjust the remaining valves as indicated; tighten locknuts to 24 N*m [18 ft-lb].
9. Install the rocker lever covers and tighten the capscrews to 24 N*m [18 ft-lb].

1. Visually inspect the wastegate actuator hose for cracks or holes. Replace if damaged.
2. Visually inspect the wastegate mounting bracket, actuator rod, and lever for damage.
3. A bent bracket, rod, or lever must be replaced. Refer to Procedure 3-05.

Tools: dial indicator, pressure gauge, regulated air pressure source

1. Attach a dial indicator so its shaft is in line with the wastegate actuator rod.
2. Set the indicator to zero, with no air pressure applied to the wastegate capsule.
3. Connect clean regulated air pressure and a pressure gauge to the capsule.
4. Apply 200 kPa [29 psi]. The rod should move approximately 5 mm [0.200 in] without sticking or air leakage.
5. No air should be heard to leak through a functional wastegate capsule.

⚠ Do not remove the pressure cap from a hot engine. Wait until the coolant temperature is below 50 C [122 F].

⚠ Coolant is toxic. Keep away from children and pets.

⚠ Never use water alone for coolant.

Tools: Drain pan with capacity of 19 liters [5 gal]

1. Drain the cooling system by opening the drain valve on the radiator and removing the plug in the bottom of the water inlet.
2. Check for damaged hoses and loose or damaged hose clamps; replace as required.
3. Fill the system with a mixture of sodium carbonate and water (0.5 kg [1.0 lb] sodium carbonate per 23 liters [6.0 gal] of water).
4. Operate the engine for 5 minutes with the coolant reaching above 80 C [176 F].
5. Shut the engine off and drain the cooling system.
6. Fill the cooling system with clean water; operate engine 5 minutes above 80 C [176 F]; drain again until water is clean.
7. Fill with a mixture of 50-percent water and 50-percent ethylene glycol antifreeze.

⚠ Avoid direct contact of hot oil with your skin.

Tools: 17 mm wrench, Container able to hold at least 20 liters [15 qt]

1. Operate the engine until the water temperature reaches 60 C [140 F]. Shut the engine off.
2. Remove the oil drain plug and drain the oil into a suitable container.
3. Clean the sealing surface, check the oil drain plug threads, and install the drain plug.
4. Torque drain plug: steel pan 80 N*m [59 ft-lb]; aluminum pan 60 N*m [44 ft-lb].

Tools: 8 mm wrench

1. Open the vent screw.
2. Operate the priming button on the lift pump until the fuel flowing from the fitting is air free.
3. Tighten the bleed screw to 9 N*m [80 in-lb].

⚠ While testing the injectors, keep hands and body parts away from the injector nozzle.

⚠ Do not bleed the fuel system on a hot engine.

Tools: 17 mm wrench, 19 mm wrench

1. Loosen one or more fittings at the injectors.
2. Crank the engine to allow entrapped air to bleed from the lines.
3. Start the engine and vent one line at a time until the engine runs smoothly.
4. Tighten the line fittings to 30 N*m [22 ft-lb].

⚠ Mechanical overtightening will distort threads, filter element seal, or filter can.

Tools: 75 to 80 mm and 90 to 95 mm filter wrenches

1. Warn the area around the fuel filter head. Remove the filter(s).
2. Clean the gasket surface of the filter head.
3. Replace the o-ring.
4. Fill the new filter(s) with clean fuel, and lubricate the o-ring seal with clean lubricating oil.
5. Install the filter as specified by the filter manufacturer.

⚠ Mechanical overtightening of filter can distort the threads or damage the filter element seal.

Tools: 90- to 95-mm filter wrench

1. Clean the area around the lubricating oil filter head.
2. Remove the filter using a 90- to 95-mm filter wrench.
3. Clean the gasket surface of the filter head; make sure the o-ring is removed.
4. Fill the filter with clean lubricating oil before installation.
5. Apply a light film of lubricating oil to the gasket sealing surface.
6. Install the filter as specified by the filter manufacturer.

1. Allow the engine to idle 3 to 5 minutes before shutting it off after a full-load operation.
2. Turn the ignition key switch to the OFF position.

⚠ Do not operate a diesel engine where there are or can be combustible vapors.

1. Disengage the driven unit, or if equipped, put the transmission in neutral.
2. With the throttle in the idle position, turn the key to the ON position.
3. Wait for the WAIT-TO-START lamp to go out, then turn the key to the START position.
4. If the engine does not start after three attempts, check the fuel supply system.
5. Idle the engine 3 to 5 minutes before operating with a load.
6. Do not operate engine at low idle for more than 10 minutes.

1. Disconnect the electrical wire from the fuel pump solenoid.
2. Rotate the crankshaft, using the starting motor, until oil pressure appears on the gauge or the warning lamp goes out.
3. Connect the electrical wire to the fuel pump solenoid valve.
4. Start the engine; refer to normal starting procedures.
5. Refer to fuel system - bleeding to vent the fuel system.