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O.S. Max-D 15 diesel

The O.S. Max-D 15 diesel is perhaps 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.

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 fine performer, but did not resonate strongly with the modelling public. Perhaps it was just too different?!? 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 late 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 may be found in my earlier article on Ron Chernich's "Model Engine News" (MEN) web-site. A test of an example of the engine will appear on this website in due course.

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