I found and old posting from a few years back called 'Is It True?' The onan L series engines were designed and built by onan for use on their DL series of gensets. They came in 3,4,and 6 cylinders with displacements of 1.7L,2.3L, and 3.4L respectively. Model designations were derived by using engine series (L) followed by number of cylinders, then displacement in Litres. Therefore, the 4 cyl was called and L423. These engines ran generator sets in the range of 15kW to 30kW. They used the Onan YD generator end. When these engines were developed, Onan was its own entity, unrelated to the
Cummins Engine Company.
Upon the purchase of Onan by Cummins in 1986, Cummins used its own designation on these engines, similar to those already used on the B and C series Cummins engines already in production at that time. They called this new, smaller engine the A series. Designations were number of cylinders, followed by series. Therefore the engine with an onan degignation of L423, became the Cummins 4A. These engines were phased out by cummins quite early, and are now nearly extinct, and very hard and expensive to get parts for. I still occasionally see some of these here in Alaska, and worked on a few when I worked for the Alaska Cummins distributor as a field generator tech. I also have a 4A myself.
