The 2.5 cc Enya 15D-I of 1956 was the first diesel to emerge from the Enya factory in Tokyo, Japan. Designed by Saburo Enya, it was a ground-breaking model in a number of ways. To begin with, it was designed from the ground up as a diesel rather than being a converted glow-plug model.

Perhaps the 15D's most notable attribute was its style of transfer porting using a single rectangular transfer port which was fed by twin bypass passages located at the front and rear. This created a form of loop scavenging which did not rely upon an upstanding piston baffle. The idea was copied by MVVS and was later further developed into the 3-port Schuerle arrangement which was to dominate model engine design from the 1960's onwards. 

Another notable feature was the use of a crankshaft of unusual main journal diameter along with a single ball-race at the rear rather than the more usual twin ball races. Saburo Enya had recognised the fact that front ball races contribute little in terms of performance to the average "consumer grade" engine, merely adding weight, manufacturing complexity and cost to the design. Others such as PAW were soon to follow. 

Despite a certain tendency of the original variant to suffer crankshaft breakages, the Enya 15D-I deservedly achieved considerable popularity, being extremely well-made as well as delivering a sparkling performance. An upgraded 15D-II version having an even higher performance coupled with enhanced structural strength appeared in 1960. This version of the engine survived in production into 1965, with a small limited edition re-release taking place years later in 2014.

A detailed article covering the start-to-finish story of the Enya 2.5 cc diesels appears elsewhere on this website.