Cummins/Onan 4CCK Generator Set

Tools: Onan carburetor wrench (4208169)

1. Run engine at normal operating temperature with almost a full load connected.
2. Turn main adjusting needle out about two full turns.
3. Turn it slowly in until engine begins to lose power and speed.
4. Turn it out very slowly until engine runs smoothly at full power and speed.
5. With no load, turn idle needle in until engine loses considerable speed, then out until smooth.

⚠ Engine starting between 6 and 15 seconds of cranking indicates the choke is properly adjusted

Tools: Straight shank of a drill bit

1. Remove the air cleaner.
2. With engine cold, measure gap between choke plate and carburetor throat using a drill bit shank.
3. Loosen the two screws on the endplate and rotate the cover assembly to obtain the listed opening.
4. Turn clockwise for less choking action, counterclockwise for more.
5. Retighten the lock screws after adjustment.

⚠ Too much sensitivity causes hunting

Tools: Voltmeter and/or frequency meter, Tachometer

1. Run plant 15 minutes under light load to normal operating temperature.
2. Adjust carburetor main jet for best mixture at full rated load.
3. Adjust carburetor idle needle with no load connected.
4. Adjust length of governor linkage and check linkage and throttle shaft for binding.
5. Adjust governor spring tension for rated speed at no load with booster disconnected.
6. Adjust governor sensitivity for closest regulation without hunting.
7. Recheck the speed adjustment.
8. Set carburetor throttle stop screw and set the vacuum speed-booster.

⚠ Low oil pressure may indicate worn main or connecting rod bearings, weak or broken by-pass spring, improperly adjusted by-pass, or a defective gage

Tools: Wrench

1. Run engine until thoroughly warmed up.
2. Loosen the locknut on the slotted stud near the breather tube.
3. Turn stud inward to increase oil pressure, outward to decrease.
4. Tighten the locknut securely after adjustment.

Tools: Feeler gages, Standard automotive-type wrench

1. Remove the valve covers.
2. Crank engine slowly by hand until left hand intake valve opens and closes.
3. Continue about 1/4-turn until flywheel mark and TC mark on gear cover are in line.
4. Check clearance; thinner gage (minimum) should pass freely, thicker gage must not.
5. Turn the self-locking adjusting screw to obtain correct clearance.
6. Crank one complete revolution, line up marks, adjust right hand cylinder valves the same way.

⚠ Do not use 12-volt coil tester; use 6-volt tester

Tools: Continuity test lamp set or timing light, Feeler gage

1. Remove the cover from the breaker box.
2. Shift breaker box to align witness marks on cylinder block and breaker box.
3. Crank engine slowly until flywheel witness mark and TC mark on gear cover align.
4. Set breaker point gap to .020 in. at full separation.
5. Turn flywheel left about two inches past the 25 degree mark.
6. Turn flywheel slowly right and note if points just separate at 19 or 25 degree mark.
7. Shift breaker box toward #1 cylinder to retard, away to advance.
8. Tighten breaker box mounting screws and reinstall cover.

⚠ Replace a grounded, open-circuited, or short-circuited armature with a new one

Tools: Test lamp set, Armature growler, Smooth steel strip

1. Lift or remove all brushes so none contact commutator or collector rings.
2. For ground test, use a continuity test lamp set: one prod on commutator, other on bare armature shaft; lamp must not glow.
3. Test ac winding between collector rings; lamp should glow.
4. For dc open circuit test, place armature in a growler; pass a smooth steel strip across commutator segments.
5. A spark at each adjacent segment pair indicates no open circuit.
6. For short circuit test, hold a steel strip about 1/2 in. above the armature laminations in a growler; magnetic attraction indicates a short.

⚠ A 12-volt tester will destroy a 6-volt coil in a few seconds; do not leave coil on tester over 15 or 20 minutes

Tools: Ohmmeter, 6-volt coil tester

1. Disconnect the spark plug leads and ground one.
2. Hold the second lead 1/4 in. from the engine.
3. Crank the engine; a good spark indicates the coil is operating.
4. Check primary winding resistance with an ohmmeter (0.5 to 2 ohms).
5. Check secondary winding resistance (4,000 to 10,000 ohms).
6. Replace coil if extremely low (short) or extremely high (open) resistance.

Tools: Flywheel puller, Gear puller and gear puller ring (Onan tool no. 420A248), Torque wrench

1. Remove housings, shrouds, blower housing and air cleaner.
2. Remove flywheel using puller or pry-bar method.
3. Remove gear cover, protecting the oil seal from keyway damage.
4. Remove crank gear using puller and gear puller ring.
5. Loosen accessories such as fuel pumps, oil filter, starter and generator.
6. Remove control box and generator; lift all generator brushes and tag all wires.
7. Drain oil and discard.
8. Remove cylinder head, then valves, springs and rocker arms; then camshaft and gear, rear bearing plate, oil pump, pistons and connecting rod bearings, and crankshaft.

⚠ Do not strike the commutator, collector rings, or bearing

Tools: Suitable bearing puller, Heavy brass rod and hammer

1. Remove the band and end cover.
2. Remove constant-pressure-type springs and lift all brushes.
3. Remove generator through stud nuts, holding end bell and frame assembly as one assembly.
4. Turn the armature nut out to the end of the armature through stud.
5. Pull outward with one hand under the armature and strike a sharp end-wise blow on the nut to loosen.
6. Remove the armature and blower as an assembly.