The 1955 MK-12S diesel of 2.5 cc displacement was one of the first competitive model diesel engines to appear in Russia. It incorporated such advanced features as a twin ball-race crankshaft, a detatchable front housing, disc rear rotary valve (RRV) induction and a remote needle valve offering minimal obstruction to air flow through the venturi. It was also quite light at just over 5 ounces.

The engine was designed by a then well-known Russian modeller named Oleg K. Gajevski. Following its initial appearance in 1955, it was manufactured in substantial numbers for the following two years until being replaced by a Webra Mach 1 clone designated the MK-12V.

Gajevski later wrote a book on model engines in which he included full details of the design and development of this engine. In addition, World Free Flight Champion Ron Draper brought an example back to England in 1956, later lending it to Peter Chinn to form the subject of a published test in "Model Aircraft" magazine. Consequently, this is one of the best-documented engines from the hard-line Iron Curtain era of the early to mid 1950's. 

The MK-12S was preceded by a high-performance prototype called the MK-12K. This was probably the most powerful 2.5 cc diesel to appear anywhere in the world as of 1955, but it proved to have an unacceptably short working life, also being subject to structural failures due to the ultra-light construction of its working components. The production MK-12S model was considerably strengthened, weighing a little more and developing considerably less power as a result.

Even so, my own tests have shown that the MK-12S was a more than adequate performer by the standards of its day. It was also built to quite acceptable standards. A full review and test appears elsewhere on this website.