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Cummins/Onan 1C 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

1
Cylinders
1800 rpm
Rated speed
0 kW
Gross power
0.946 L
Oil capacity
On this pageSpecsGenerator setsMaintenanceFAQ

Engine specifications

Oil capacity0.946 L
Cylinders1
Aspirationair-cooled L-head
Rated speed1800 rpm
Gross power0 kW

Generator sets powered by this engine

1
Cummins/Onan 1C-series

How to read your Cummins/Onan engine serial & model number →

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

ItemSpecCapacityPart #Interval
Air filterClean and oil regularly—50 hr
Fuel filterClean strainer screen—200 hr
OilSAE No. 30 (above 90F)1.0 quart—100 hr
Spark plugGap 0.024-0.026 inch—200 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..