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Cummins Onan Engines and Generators


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Welcome to our Onan generator page. This page is devoted to Onan air-cooled generators, which I have spent 40 years servicing and representing on the distributor level. Over the years, I have become quite comfortable working on Onan gensets and engines. In this page I will try to put down some of the information I have acquired starting with the early units and bringing you up to the present.

The Early Years

By attending various schools on Onan generators, I acquired information on the beginnings and development of Onan. I first visited the Onan factory in Minneapolis, Minnesota for a school in 1968. Here is a brief timetable of information I have on their early development by DW Onan through their purchase by Cummins Engine Co.

  • 1920 - Onan started in business.
  • 1925 - They purchased 25 model FE engines from Briggs & Stratton.
  • 1927 - They built a ten light generator.
  • 1930 - The first engine was built.
  • 1932 - The first Gen Set was produced.
  • During World War II, Onan supplied 85% of the military generators.
  • 1946 - The Onan Corporation was formed.
  • 1960s - Studebaker purchased Onan and introduced the J series air-cooled engine.
  • 1975 - Hawker Siddeley bought 33% of Onan.
  • 1979 - McGraw Edison bought 67% of Onan from Studebaker.
  • 1985 - Onan now has 92.3% of the Recreational Vehicle market.
  • 1986 - Cummins Engine Co begins the acquisition of Onan Corp.
  • 1992 - Cummins Engine Co completes the acquisition of Onan Corp.
  • 1997 - Onan closes its Huntsville engine manufacturing plant and sells their tooling and technology to Linamar Corp of Canada.
  • 1997 - Linamar starts producing Performer and Elite engines for Onan in a new plant in Guelph, Ontario.
  • 2000 - Onan contracts with Fuji/Robin to manufacture their OHV EH64 Horizintal V-twin engine for Onan for the welder industry.
  • 2003 - Linamar stops producing Performer engines for Onan and Onan exits the small gasoline engine business.
  • 2004 - Fuji/Robin stops making Onan branded engines for the welder market and transitions to making Suburu/Robin engines for the welder industry.
  • 2005 - Linamar stops producing two cylinder Performer engines sold under the Linamar name.
  • 2007 - Onan changes it name and Logo to Cummins Onan and starts a new website at http://www.cumminsonan.com/.

Onan became a leader in the small genset field with their two cylinder, opposed piston design, which was made through 2005. This design proved to be a winner, especially with the RV industry. The Emerald and Marquis are popular genset models using this design. I first started working on their gensets in 1968 at the distributor level. I believe it may be helpful to list some of the units of this era and work toward the present. Below I have included two tables of information that may be useful if you are working on an Onan genset. Most of this information is based on popular RV gensets, but may be applicable to other models.

Their were many variations of there engines and gensets and it would be impossible to cover all of them here. The first table is of the early RV type gensets built prior to Cummins taking over the company in the mid 80's. The LK and CCK were the early workhorses, cast iron engines running at 1800 rpm. Many of these are still out there running well and are a real gem if you can find one for a cabin or standby power. The little AJ ran at 3600 and was quite noisy. The BF, BFA, BGA and NH series introduced the aluminum engine design which was used in the Emerald and Marquis RV gensets and the "Performer" industrial engines.

The Newer Units

Onan Emerald genset The second table list the newer RV type gensets. The two cylinder units including the Emerald and Marquis use the B and NH engines mentioned above. These engines are known as the "Performer" in the industry and are used on many lawn tractors, welders, as well as the gensets.

In the mid 80's, the Emerald became the standard of the industry and the Marquis includes additional premium features like an electronic governor and sound proofing. The two cylinder, 1800 rpm design can't be beat and all the 3600 rpm units out there are just not in the same league. The Performer engine continues to live on with the production of the engines being moved from Huntsville, Alabama to Ontario, Canada in 1997. Linamar Corporation of Canada built a brand new 100,000 square foot building in Guelph, Ontario for engine production. They took over the manufacturing of the Performer engines under a partnership with Onan. You can see quality Performer engines under both the Onan and Linamar names. Currently, to meet EPA mandates, the Onan two cylinder engines have gone to an overhead valve engine. The L-head Performer is not being sold by Onan anymore in the USA.

The Microlite gensets use a single cylinder, overhead valve engine running at 3600 rpm's. They run very quiet due to the special sound proof compartment they are housed in. The Microlite units come with everything mounted inside the housing, including the muffler, which makes them fairly easy to install.

Use this link to locate an Onan dealer worldwide: http://www.cumminsonan.com/locator



How to identify which engine or genset you have:

Example: Model/Spec - 4.0BFA-1R/16000C (spec letter is C) - (Genset)
Example: Model/Spec - B48G-GAO20/4235F (spec letter is F) - (Engine)

Example: Serial Number - (Oldest) 62C876543 - (Old) 0372129176 - (New) C763611296
Oldest - 6=month, 2=year, C=decade
(A=1940-1949 B=1950-1959 C=1960-1969)
Old - 03=month, 72=year
New - C=month, 76=year, 3=Code
Note: Actual serial number is the last 6 digits. Prior to 1952, a period or dash was sometimes used instead of a letter.

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Home Page
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Below are two tables of useful reference information for Onan specifications.
The Precise Engine Repair site is maintained by Bruce Perrault.

Early Gensets

AJ
2.7kw - 3kw

BF
4kw

BFA
4kw

BGA
5kw

CCK
4kw - 5kw

LK
2.5kw

NH
6.5kw

Generator Design1

Revolving Arm Revolving Arm Revolving Arm Revolving Arm Revolving Arm Revolving Arm Revolving Arm

Starting System2

Exciter Crank Exciter Crank Exciter Crank Exciter Crank Exciter Crank Exciter Crank Exciter Crank

Engine

Cast Iron Aluminum Aluminum Aluminum Cast Iron Cast Iron Aluminum

# Cylinders

one two two two two one two

Engine RPM

3600 1800 1800 1800 1800 1800 1800

Weight

147/160 lbs 217 lbs 235 lbs 285 lbs 290/315 lbs ? 305 lbs

Horsepower

5.5 8.5 8.5 10 10 5 14

Displacement

14.9in 40.25in 43.3in 43.3in 49.8in 24.9in 60.0in

Compression Ratio

6.25:1 7:1 7:1 6.9:1 5.5:1 5.5:1 7:1

Bore Size

2.75in 3.125in 3.25in 3.25in 3.25in 3.25in 3.56in

Stroke

2.50in 2.625in 2.625in 2.87in 3.0in 3.0in 3.0in

Oil Capacity3

1.1 / 2qts 4qts 3.5qts 3.5qts 3.5qts 2 qts 3.5qts

Voltage

120 120/240 120 120/240 120/240 120 120/240

Amps @ 120v

23 - 25 33.3 33.3 41.6 33.6 - 41.6 20.8 54.2

Battery Charge Rate

1-2 amps 1-1.5 amps 1-1.5 amps 1-1.5 amps 1.5-6 amps 1-2 amps 1-1.5 amps

Spark Plug Gap4

.025 .025 .025 .025 .025 .025 .025

Point Gap

.022 .025 .021 .021 .020 .020 .020

Ignition Timing5

22o BTC 21o BTC 21o BTC 21o BTC 19o BTC 19o BTC 21o BTC

Valve Lash6 Intake
Exhaust

.011
.011
.003
.010
.003
.010
.003
.010
.006
.015
.008
.016
.003
.012

Compression7

100-120 PSI 100-120 PSI 100-120 PSI 100-120 PSI 100-120 PSI 100-120 PSI 100-120 PSI

1 A revolving armature has both a commutator and slip rings.
2 Exciter crank means that the main armature cranks the engine.
3 This is an approximate amount. Always check the dipstick.
4 Set the gap at .018 for propane fueled engines.
5 In general, the timing of the aluminum engines is set by the breaker gap. The LK and CCK had adjustable timing by moving the point box.
6 Valve lash is always set with engine cold.
7 Compression is measured with the engine hot.


Newer Gensets

KV
Microlite

KY
Microlite

BGE
Emerald

BGM
Marquis

NHM
Marquis

NHE
Emerald

NHD
Commercial

Watts

2800 4000 4000 5500 7000 6500 6500

Generator1 Design

Revolving Field Revolving Field Revolving Field Revolving Field Revolving Field Revolving Field Revolving Field

Starting2 System

Auto Type Auto Type Auto Type Auto Type Auto Type Auto Type Auto Type

Engine Type

GH-200 E095H P218 P218 N60V N60V N60V

Cylinders

1 cyl OHV 1 cyl OHV 2 cyl L-head 2 cyl L-head 2 cyl L-head 2 cyl L-head 2 cyl L-head

Engine RPM

3600 3600 1800 1800 1800 1800 1800

Weight

113 lbs 172 lbs 216 lbs 258 lbs 272 lbs 230 lbs 230 lbs

Horsepower

7 bhp 9.5 bhp 10.3 bhp 10.3 bhp 14 bhp 14 bhp 14 bhp

Displacement

12 cu in 18.5 cu in 47.7 cu in 47.7 cu in 60 cu in 60 cu in 60 cu in

Compression Ratio

8.5:1 8.5:1 6.9:1 6.9:1 7:1 7:1 7:1

Bore Size

2.64 in 3.11 in 3.25 in 3.25 in 3.56 in 3.56 in 3.56 in

Stroke

2.2 in 2.44 in 2.87 in 2.87 in 3.0 in 3.0 in 3.0 in

Oil Capacity

1 qt 1.6 qts 3.5 qts 3.5 qts 3.5 qts 3.5 qts 3.5 qts

Voltage

120 120 120 120 120 120 120 / 240

Amps @ 120v

23.3 33.3 33.3 45.8 56.7 54.2 54 / 27

Fuel3 Consumption

0.3 gph 0.48 gph 0.6 gph 0.7 gph 0.7 gph 0.7 gph 0.7 gph

Sound Level4

70 dB(A) 70 dB(A) 74.5 dB(A) 73 dB(A) 74 dB(A) 77 dB(A) 75 dB(A)

Spark Plug Gap5

.025 .025 .025 .025 .025 .025 .025

Valve Lash6 Intake
Exhaust

.002
.002
.002
.002
.005
.013
.005
.013
.005
.013
.005
.013
.005
.013

Compression7

? ? 75-115 75-115 100-120 100-120 >100-120

1 A revolving field generator has a rotor with two slips rings and brushes.
2 Automotive starting system uses a starter drive and ring gear.
3 Average fuel consumption is measured with the genset running at half load.
4 Sound level is measured at a distance of 10 feet at full load.
5 The current gensets use breakerless ignition and have non-adjustable timing.
6 Valve clearance is measured with the engine cold.
7 Compression is measured with the engine hot.