Cummins/Onan 1C Engine Engine
The Cummins/Onan 1C is a 1-cylinder air-cooled l-head engine rated at 1800 rpm, producing up to 0.81 kW. It powers generator sets from Cummins/Onan, including the 1C-series. It holds 0.95 L (0.2 gal) of oil.
Also known as: Onan 1C
Engine specifications
| Oil capacity | 0.946 L |
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| Cylinders | 1 |
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| Aspiration | air-cooled L-head |
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| Rated speed | 1800 rpm |
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| Gross power | 0 kW |
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Generator sets powered by this engine
1Cummins/Onan 1C-series
Common problems
11- SHARP METALLIC THUD, ESPECIALLY WHEN COLD ENGINE FIRST STARTED
Cause: Low oil supply. Oil badly diluted.
Fix: Add oil. Change oil. - PINGING SOUND WHEN ENGINE IS RAPIDLY ACCELERATED OR HEAVILY LOADED
Cause: Carbon in cylinder.; Spark too early.; Wrong spark plug.; Spark plug burned or carboned.; Valves hot.
Fix: Remove carbon.; Adjust breaker points or retime magneto.; Install correct spark plug.; Install new plug.; Adjust tappet clearance. - LIGHT POUNDING NOISE
Cause: Loose connecting rod bearing.
Fix: Adjust or replace. - HOLLOW CLICKING SOUND WITH COOL ENGINE UNDER LOAD
Cause: Loose piston.
Fix: If noise only slight and disappears when engine warms up, no immediate attention needed. otherwise replace worn parts. - EXCESSIVE OIL CONSUMPTION, LIGHT BLUE SMOKY EXHAUST
Cause: Poor compression, usually due to leaking valves.
Fix: Oil leaks from oil base or connections. 'This does not cause smoky exhaust. - ENGINE WILL NOT START WHEN CRANKED
Cause: Faulty ignition.
Fix: Clean, adjust, or replace breaker points, plug, condenser, etc., or retime magneto. - ENGINE STOPS UNEXPECTEDLY
Cause: Fuel tank empty.
Fix: Refill. - ENGINE RUNS BUT VOLTAGE DOES NOT BUILD UP
Cause: Poor commutation.
Fix: See that brushes seat well on commutator, are free in holders, are not worn shorter than 5/8 - ENGINE CRANKS TOO STIFFLY
Cause: Too beavy oil in crankcase.
Fix: Drain, refill with lighter oil. - DULL METALLIC THUD. IF NOT BAD, MAY DISAPPEAR AFTER FEW MINUTES OPERATION. IF BAD, INCREASES WITH LOAD.
Cause: Loose crankshaft bearing.
Fix: Replace, unless one of the next two remedies permanently corrects the trouble. - BACK,SMOKEY EXHAUST, EXCESSIVE FUEL CONSUMPTION, FOULING OF SPARK PLUG WITH BLACK SOOT, POSSIBLE LACK OF POWER UNDER HEAVY LOAD
Cause: Fuel pressure too rich.
Fix: Adjust carburetor or choke. Install needed carburetQr parts.
Compiled from service & troubleshooting documentation across every generator set that uses the Cummins/Onan 1C.
Maintenance schedule
| Item | Spec | Capacity | Part # | Interval | |
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| Air filter | Clean and oil regularly | | — | 50 hr | find |
| Fuel filter | Clean strainer screen | | — | 200 hr | find |
| Oil | SAE No. 30 (above 90F) | 1.0 quart | — | 100 hr | |
Pooled from every document that names this exact engine — confirm the interval and part number against your unit's serial number.
Common questions
What is the oil capacity of the Cummins/Onan 1C?
The Cummins/Onan 1C engine has an oil capacity of 0.946 liters.
Which generators use the Cummins/Onan 1C engine?
The Cummins/Onan 1C powers 1 generator set(s), including Cummins/Onan 1C-series.
How often should you change the oil in the Cummins/Onan 1C?
The Cummins/Onan 1C oil change interval is every 100 hours.
What is a common problem with the Cummins/Onan 1C engine?
A commonly reported issue on generators using the Cummins/Onan 1C is: SHARP METALLIC THUD, ESPECIALLY WHEN COLD ENGINE FIRST STARTED. Cause: Low oil supply. Oil badly diluted.. Fix: Add oil. Change oil..