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.

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.

Onan became a leader in the small genset field with their two cylinder, opposed piston design. This design proved to be a winner, especially with the RV industry. The Emerald and Marquis are the current 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 is still used in the Emerald and Marquis RV gensets today and the "Performer" industrial engines.

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 have taken 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 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.

Visit the Onan section of our WebStore if your need is genuine service manuals or parts. You may find out more about Onan by clicking the Onan logo below to visit there website.

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 - (newer)C763611296

Below are two tables of useful reference information we have on Onan specifications

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.

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.