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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

15
  • Excessive oil consumption, light blue smoky exhaust
    Cause: Poor compression, usually due to leaking valves
    Fix: Tighten cylinder head and plug; if still not corrected, grind or replace valves
  • Voltage drops under heavy load
    Cause: Engine lacks power
    Fix: See remedies for engine misfires under heavy load
  • Engine will not start when cranked
    Cause: Faulty ignition
    Fix: Clean, adjust, or replace breaker points, plug, condenser, etc., or retime magneto
  • Excessive arcing of brushes
    Cause: Rough commutator or rings
    Fix: Turn down
  • Engine misfires at heavy load
    Cause: Spark plug gap too wide
    Fix: Adjust gap
  • Engine backfires at carburetor
    Cause: Lean fuel mixture
    Fix: Clean or adjust carburetor
  • Voltage unsteady but engine not misfiring
    Cause: Speed too low
    Fix: Adjust governor to correct speed
  • Engine misfires at light load
    Cause: Spark plug gap too narrow
    Fix: Adjust to correct gap
  • Light pounding knock
    Cause: Loose connecting rod bearing
    Fix: Adjust or replace
  • Black smoky exhaust, excessive fuel consumption, fouling of spark plug with black soot, possible lack of power under heavy load
    Cause: Fuel mixture too rich
    Fix: Adjust carburetor or choke; install needed carburetor parts
  • 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", and have good spring tension
  • Engine cranks too stiffly
    Cause: Too heavy oil in crankcase
    Fix: Drain, refill with lighter oil
  • Tappet clearance too great
    Fix: Adjust or replace tappets
  • Light dim at far end of line but bright near power plant
    Cause: Too small line wire for load and distance
    Fix: Install larger or extra wires or reduce load

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: Excessive oil consumption, light blue smoky exhaust. Cause: Poor compression, usually due to leaking valves. Fix: Tighten cylinder head and plug; if still not corrected, grind or replace valves.