Cummins/Onan 12.5 RDJC Generator Set

⚠ Shut down the set and disconnect the battery cable, negative (-) terminal first, before setting the breaker point gap

1. Locate the start-disconnect centrifugal switch on the side of the engine, above the oil filter.
2. If necessary, loosen the stationary contact and adjust the point gap to 0.020 inch (51 mm).
3. Replace burned or faulty points.

⚠ Avoid overcharging the battery

⚠ Do not smoke or allow any flame, sparks, or arc-producing devices in the battery area

1. Locate the adjustable resistor slide tap in the charging circuit, found in the generator air outlet.
2. If necessary, increase the charging rate slightly by moving the slide tap up.
3. Make small increments of change until the proper rate has been determined.
4. Adjust this slide tap only when the engine is stopped.

⚠ High voltages can cause injury or death; use extreme caution when working on electrical components

Tools: Screwdriver, Wrench

1. Move the Run/Stop/Remote switch on the engine control panel to the Run position.
2. Move the Phase Selector switch to read generator output current and voltage.
3. Insert a screwdriver into the Voltage Adjust potentiometer and carefully loosen the locking nut with a wrench.
4. While observing the voltmeter, slowly turn the screwdriver clockwise to increase voltage or counterclockwise to decrease voltage.
5. Adjust to the rated nameplate voltage.
6. Tighten the locking nut, being careful not to change the adjustment.
7. Move the Phase Selector switch to the Off position.

1. Turn the sensitivity adjusting ratchet to adjust governor sensitivity (no-load to full-load speed droop).
2. Radiator cooled sets: turn the ratchet clockwise for more sensitivity (less speed drop at full load).
3. Radiator cooled sets: turn the ratchet counterclockwise for less sensitivity (more speed drop).
4. City water cooled sets: turn the ratchet counterclockwise for more sensitivity.
5. After making the sensitivity adjustment, readjust the speed.

Tools: Stroboscope, Frequency meter

1. Turn the governor speed adjusting nut clockwise (more spring tension) to increase rpm.
2. Turn the nut counterclockwise to reduce governed speed.
3. Use a stroboscope or a frequency meter to make this adjustment.

⚠ Incorrect valve clearance adjustment can lead to irrevocable damage to the generator set; only qualified personnel should perform this adjustment

Tools: Socket wrench, Feeler gauge, Torque wrench

1. Check the valve clearance when the engine is at room temperature, about 70°F (21°C).
2. Turn the flywheel until the cylinder to be adjusted is on its compression stroke.
3. Turn the flywheel an additional 10 to 45 degrees clockwise so the piston is in its power stroke with both valves closed.
4. Check cylinder head-bolt torque prior to valve clearance adjustment.
5. Loosen the locknut securing the rocker arm to the cylinder head to increase clearance; tighten it to reduce clearance.
6. Using a feeler gauge, check the clearance between the rocker arm and the valve until the proper gap is established.

⚠ Do not smoke or allow any source of ignition while servicing batteries

⚠ Always remove the negative (-) cable first, and reconnect it last to prevent arcing

Tools: Battery hydrometer

1. Disconnect the negative ground strap from the battery before working on any part of the electrical system or engine.
2. Wipe the batteries clean with a damp cloth whenever dirt appears excessive.
3. If corrosion is present, remove battery cables and wash terminals with an ammonia solution or a solution of 1/4 pound baking soda in 1 quart of water.
4. Flush the outside of the battery and surrounding areas with clean water.
5. Coat the terminals with a light application of petroleum jelly or non-conductive grease.
6. Use a battery hydrometer to check the specific gravity of the electrolyte in each cell; hold the hydrometer vertical.
7. Correct the reading by adding four gravity points (0.004) for every ten degrees the electrolyte temperature is above 80°F (27°C).

⚠ Filters should be handled with care to prevent damage; if the filter becomes damaged, install recommended replacement part

1. Remove pre-cleaner and wash out dirt; dry and reinstall.
2. Loosen clamp and remove end cover.
3. Remove thumbscrew and take out element.
4. Wash element in detergent and water (use new element after 6 washings); dry and reinstall.
5. Remove air cleaner baffle from cover, wash out dirt, and reinstall in cover.
6. Install cover with "TOP" up and tighten clamp.

1. Remove hose clamp, breather hose, breather cap clamp and insulator halves to release breather cap and valve assembly.
2. Wash cap, valve assembly and baffle in suitable solvent.
3. Dry and reinstall.

⚠ Hot crankcase oil can cause burns if spilled or splashed on skin; keep fingers and hands clear when removing the oil drain plug and wear protective clothing

Tools: Drain pan

1. Stop the engine and drain the crankcase oil while the engine is still hot.
2. Place a pan under the drain outlet and remove the oil drain plug or open the oil drain valve.
3. After the oil is completely drained, replace the drain plug or close the drain valve.
4. Replace oil filter if necessary before adding oil.
5. Refill with oil of the correct API designation and SAE viscosity grade for the temperature conditions.

⚠ Hot crankcase oil can cause burns if spilled or splashed on skin

Tools: Container

1. Place a container under the oil filter and remove the filter by turning it counterclockwise.
2. Clean the filter mounting area.
3. Coat the oil filter gasket with clean oil.
4. Install the new filter by turning it clockwise until the gasket touches the mounting base.
5. Tighten the filter 1/2 turn.

1. Exercise the generator set until the engine is up to operating temperature.
2. Shut down the engine; disconnect battery and store in a cool, dry place. Connect battery to a charger every 30 days.
3. Drain the oil base while it is still warm; refill and attach a warning tag indicating the viscosity of oil used.
4. Service the air cleaner.
5. Clean throttle and governor linkage and protect by wrapping with a clean cloth.
6. Plug the intake and exhaust outlets to prevent entrance of moisture, bugs, dirt, etc.
7. Clean and wipe the entire unit; coat parts susceptible to rust with a light coat of grease or oil.
8. Provide a suitable cover for the entire unit after the unit has cooled down.