The OK Cub series of radially-ported glow-plug motors began to appear in June 1949 when the first of the series, the long-stroke Cub .049, was released to a very enthusiastic reception. By the end of 1949 the Cub series had grown to include additional models in both .074 and .099 cuin. displacements. These little engines were all trend-setters in their respective displacement categories. All three models were to remain on offer for the remainder of OK's market presence, although they were subject to a number of design changes along the way.
The emerging importance of the 2.5 cc (.15 cuin.) displacement category in International competition eventually led to the 1952 introduction of a .147 cuin. model called the Cub .14. This was followed in 1953 by the first commercially-promoted OK Cub diesel, the Cub .075D, which was basically a diesel conversion of the existing Cub .074 glow-plug model. It had been preceded by a pair of very low-production experimental diesels in .06 and .15 cuin. displacements.
1954 saw the introduction of a .19 cuin. version of the earlier Cub .14. That same year also saw the introduction of a diesel version of the Cub .049 which joined its .075 diesel companion in the range.
In 1955 the Cub line-up was expanded still further with the introduction of the Cub .29 and Cub .35 models. These were the largest-displacement OK Cubs. Although styled somewhat differently from the smaller Cubs, they retained the crankshaft front rotary valve (FRV) induction and radial cylinder porting of their smaller relatives.
The smallest OK Cub model, the reed valve .024, appeared in 1960. Oddly enough, it was basically a miniaturized reed valve version of the two largest OK Cubs, the .29 and .35. As events were to prove, it was not a great success, besides which the company was already mired in financial difficulty. All OK model engine production ended in 1964.
A detailed analysis of the original 1949 OK Cubs by Maris Dislers may be found elsewhere on this website. In addition, a very informative pdf presentation on the OK enterprise by David Burke may be accessed through this link. Finally, a good deal of fascinating information on the history of OK may be found in Ted Brebeck's book "They Should Have Kept the Bear"