The O.S. Max-D 15 diesel is one of the least familiar member of the classic lineup from the O.S company of Osaka, Japan. Development of this very high quality twin ball-race 2.5 cc (.15 cuin.) diesel commenced in early 1957, presumably in response to the late 1956 appearance of the ground-breaking Enya D15-I.  A strong rivalry always existed between O.S and Enya, with the two Japanese companies continually covering each others' moves! However, various factors delayed the market appearance of the O.S. Max-D 15 until mid 1959, by which time the design was no longer competitive. 

The Max-D 15 displayed several unusual features, the most notable being its use of a baffle piston. This required the provision of means to keep the contoured contra piston in the correct alignment to match the baffle. The engine employed conventional cross-flow loop scavenging, in contrast to its Enya rival which used an early form of Schnuerle porting. 

The Max-D 15 was a good performer, but did not resonate strongly with the modelling public. Perhaps it was just too different?!? Or perhaps it was the engine's somewhat difficult starting. Regardless of the reason, production figures appear to have been quite modest - the engine is very rare today.  Production seems to have ceased altogether in mid 1960. A few of the left-over cases were built up into high-performance glow-plug engines which performed at extremely competitive levels by the standards of their day. 

The full story of the O.S. Max-D 15, including a bench test, may be found elsewhere on this website.