Cummins/Onan 4.5 MCE Generator Set

⚠ A hot choke cover can cause burns.

1. Remove plastic cover from bi-metal coil/electric heater assembly.
2. Check choke lever returns automatically and smoothly.
3. Rotate heating element until choke plate is halfway open.
4. Rotate heater cover counterclockwise while tapping choke lever until it no longer bounces (reference position).
5. Rotate heater cover clockwise the degrees listed in Table 6-1 for ambient temperature.
6. Lock cover in place and replace plastic cover.

Tools: Voltmeter

1. Check no-load output voltage between L1-L0 or L2-L0.
2. Confirm 123-132 VAC at 63 Hz and 105-115 VAC at 52 Hz.
3. Reconnect leads TX and T21-X as shown in Figure 8-2 to adjust voltage to specification.

⚠ Binding can cause erratic governor action.

1. Loosen lock nut at ball joint and unsnap socket from ball.
2. Push governor rod gently toward carburetor to full-throttle position.
3. Turn socket to lengthen or shorten rod so ball and socket line up.
4. Snap socket back over ball.
5. Tighten lock nut while holding socket square with ball axis.
6. Keep crook at throttle end of rod level.
7. Rotate governor and check for binding; readjust if necessary.

⚠ Disconnect voltage and frequency sensitive devices before adjusting.

Tools: Voltmeter, Frequency meter

1. Disconnect all loads and check no-load frequency.
2. Turn idle mixture screw clockwise until frequency drops, then counterclockwise until it drops again.
3. Set screw for highest possible stable frequency.
4. Check output voltage: 123-132 VAC at 63 Hz or 105-115 VAC at 52 Hz.
5. Push adjustment limiter cap over mixture screw head.

1. Start set and warm up ten minutes under 1/2 to 3/4 rated load.
2. Disconnect load and turn governor speed adjusting screw for 50 Hz (40 Hz).
3. Set idle speed stop screw so it does not touch throttle lever tang.
4. Turn idle speed stop screw for 55 Hz (45 Hz).
5. Turn governor speed adjustment nut for no-load 62-63 Hz (51.5-52.5 Hz).

Tools: 9/16 tappet wrench, 7/16 tappet wrench, Feeler gauge

1. Rotate crankshaft clockwise and watch intake valve on left side open and close.
2. Align TC mark on flywheel with TC mark on gear cover.
3. Confirm intake and exhaust valves on right side are both closed.
4. Adjust right side tappets to 0.010 inch clearance with 9/16 and 7/16 tappet wrenches.
5. Rotate crankshaft one full turn, align marks, and adjust left side tappets.
6. Rotate crankshaft one full turn and recheck right side clearances.

⚠ Disconnect battery cables (negative first) to prevent accidental starting.

Tools: Wire gauge

1. Remove resonator/flame arrestor assembly.
2. Remove access cover for brush assembly.
3. Check brushes for wear with wire marked 1 inch from one end.
4. Remove brush holder by disconnecting two leads and two mounting screws.
5. Install new brushes and springs, holding with wire through holder.
6. Align holder so brushes are centered on slip rings, then tighten.
7. Connect B+ lead to outer brush terminal, B- lead to inner terminal.

Tools: Wire brush, Torque wrench

1. Drain engine coolant and disconnect coolant hoses from cylinder heads.
2. Remove cylinder head bolts and pull off cylinder heads.
3. Remove carbon deposits with a wire brush.
4. Install new head gaskets.
5. Reinstall heads, torquing bolts in sequence in steps of 5 ft-lbs to 29-31 ft-lbs.
6. Reconnect hoses and refill engine with coolant.
7. Retorque head bolts when set has run 25 hours.

⚠ Most parts cleaning solutions are flammable.

1. Disconnect fuel line, governor rod, breather tube, vacuum lines and choke wires.
2. Unbolt carburetor from intake manifold.
3. Disconnect choke links and remove carburetor adapter.
4. Remove throttle and choke plate retaining screws and pull out shafts.
5. Remove main and idle mixture screws.
6. Separate fuel bowl from upper section.
7. Note float assembly positions before sliding out retaining pin.
8. Unscrew needle valve seat.

⚠ Forcing the mixture screw tight will score the needle and seat.

1. Install throttle shaft and plate with new screws, centering plate in bore.
2. Install idle mixture screw, turn in by hand until lightly seated, back out one turn.
3. Install needle valve and seat, bowl gasket and float assembly.
4. Check float level upside down; bend tab to adjust to 0.59-0.63 in (15-16 mm).
5. Install float bowl and main mixture screw; seat lightly, back out 1-1/4 turns.
6. Reinstall carburetor and adjust per Governor/Carburetor Adjustments.

Tools: Piston ring compressor, Plasti-gage (green), Torque wrench

1. Turn crankshaft until crankpins are at bottom of stroke.
2. Lubricate pistons and cylinders and compress rings with a ring compressor.
3. Position piston/rod assemblies with connecting rod cap bolt offsets outward.
4. Tap pistons down with wood hammer handle until rods seat on crank pins.
5. Use Plasti-gage (green code) to check crankpin bearing clearance.
6. Lubricate crankpin, attach cap, torque cap bolts to specification.
7. Confirm rod moves freely side-to-side; loosen and retap cap if not.
8. Crank engine by hand to check all bearings are free.

⚠ Neoprene impeller disintegrates in seconds if pump run dry.

Tools: Pliers

1. Press in new water seal; lubricate bore and seal lip with vasoline.
2. Press new bearings onto shaft from pulley end; snap retaining ring into place.
3. Install plastic washer and O-ring; insert shaft assembly until it bottoms.
4. Assemble wear plate, cam and impeller; lubricate wear surfaces.
5. Secure pump cover and gasket.
6. Secure pulley and mount pump; align pulleys and adjust belt tension.