Cummins/Onan JB Engine

⚠ Injectors must always be adjusted before valves.

⚠ Be careful not to bruise injector tip.

Tools: Inch-pound torque wrench (Snap-On Model TQ12B or equivalent), Screwdriver adapter, Feeler gauge, Wire gauge

1. If used, pull compression release lever back and block open.
2. Bar engine in direction of rotation until No. 1 VS mark appears.
3. Adjust injector plunger, then crossheads and valves of first cylinder.
4. Turn crankshaft to next VS mark per firing order; adjust that cylinder.
5. Continue until all injectors and valves are adjusted.
6. Injector plungers adjusted with inch-pound torque wrench to torque setting.
7. Warm engine to 140°F oil temperature and reset injectors to warm setting.
8. Always make final valve adjustment after injectors and with engine at operating temperature.

⚠ Air housing door must be on when operating engine

Tools: Screwdriver

1. Loosen power element mounting screws in slotted holes
2. Slide assembly until plunger rests on roll pin with shutter closed
3. Shutter must be closed at ambient temperature
4. Test element by heating: plunger moves out at about 120F
5. Total plunger movement should be at least 13/64 in

⚠ Do not force needle valves against seats

Tools: Screwdriver

1. Allow engine to warm up
2. At no load turn idle adjustment out until speed drops slightly
3. Turn needle in until speed returns to normal
4. Apply full load, turn main adjustment in until speed drops
5. Turn needle out until speed returns to normal

⚠ Oversensitive adjustment may cause hunting

Tools: Reed frequency meter, Wrench

1. Hold governor spring stud, turn nut to set speed
2. Use a reed type frequency meter on generator AC output
3. Prior Spec R: turn spring stud counterclockwise for more sensitivity
4. Adjust for maximum sensitivity without hunting
5. Begin Spec R: turn speed nut clockwise to increase speed
6. Begin Spec R: turn ratchet nut counterclockwise to increase spring tension

Tools: Feeler gauge

1. Adjust valves in firing order 1-2-4-3
2. Set timing and clearance for cylinder 1
3. Turn flywheel 180 degrees for cyl 2, between 10 and 45 deg past BC
4. Adjust cylinder 2 clearance
5. Turn 180 degrees for cyl 4, between 10 and 45 deg past TC, adjust
6. Turn 180 degrees for cyl 3, between 10 and 45 deg past BC, adjust

⚠ Set clearances at room temperature, at least two hours after shutdown

Tools: Feeler gauge, Torque wrench

1. Turn flywheel to compression stroke after intake valve closes
2. Align TC mark with timing pointer, then turn clockwise 10 to 45 degrees
3. Check cylinder head bolt torque
4. Check rocker-arm-to-valve clearance with feeler gauge
5. Adjust with locknut to Table 3 clearance

⚠ Early model four-cylinder engines do not have a BC mark on the flywheel

Tools: feeler gauge

1. Adjust valve clearance in firing order (1-2-4-3) sequence
2. Set timing for number 1 cylinder and adjust the valve clearance
3. Turn flywheel clockwise 180 degrees for number 2 cylinder (between 10 and 45 degrees past BC mark)
4. Adjust valve clearance for number 2 cylinder
5. Turn flywheel clockwise 180 degrees for number 4 cylinder (between 10 and 45 degrees past TC mark)
6. Adjust valve clearance for number 4 cylinder
7. Turn flywheel clockwise 180 degrees for number 3 cylinder (between 10 and 45 degrees past BC mark)
8. Adjust valve clearance for number 3 cylinder

Tools: feeler gauge, torque wrench

1. Turn flywheel until cylinder to be adjusted is on its compression stroke
2. Turn flywheel until TC mark lines up with timing pointer, then turn clockwise an additional 10 to 45 degrees
3. Check cylinder head-bolt torque (see Fig. 60)
4. Using a feeler gauge, check clearance between rocker arm and valve
5. Increase or reduce clearance until proper gap is established, adjusting with the locknut
6. Refer to Table 3 for correct valve clearance setting

⚠ Avoid overcharging.

1. Set slide tap on adjustable resistor R21 in generator air outlet to give about 2 amperes charging rate.
2. If charge winding AC output is below 19 volts on 12 volt battery charge models, 38 volts on 24 volt models, 50 volts on 32 volt models, test charging circuit for opens or grounds.
3. If a separate automatic demand control is used, adjust charge rate for maximum 4.5 amperes.

⚠ Never roll or tighten a belt over the pulley and never pry it on with a tool such as a screwdriver.

⚠ When two or more belts are used, they must be replaced as a set.

⚠ Do not tighten belt beyond figures given to eliminate belt squeak.

1. Shorten distance between pulley centers so belt can be installed without force.
2. Tighten belts so pressure of the index finger will depress belt to specified deflection.
3. All new belts will loosen after running an hour or more and must be retensioned.
4. If belt can be pushed down 1/8 inch more than recommended, retension.
5. To clean a belt, wipe with approved belt lubricant or hydraulic brake fluid.

⚠ Do not force needle valves against their seats; this will bend the needle.

Tools: Screwdriver (adjusting needles)

1. Be sure ignition and governor are adjusted and allow engine to warm up.
2. With no generator load, turn idle adjustment out until speed drops slightly below normal, then in until speed returns to normal.
3. Apply full load and carefully turn main adjustment in until speed drops slightly below normal, then out until speed returns to normal.

⚠ An over-sensitive adjustment may result in a hunting condition.

Tools: Wrench, Reed type frequency meter or mechanical tachometer

1. Adjust engine speed by turning governor speed adjusting nut; clockwise increases speed, counterclockwise decreases.
2. Adjust sensitivity by turning the sensitivity adjusting ratchet nut through hole in the blower housing.
3. If speed drops too much at full load, turn ratchet nut counterclockwise to increase spring tension.
4. After adjusting, replace dot button in blower housing and secure speed stud lock nut.