The OK diesels represented one of the final attempts by an American mass producer of model engines to market the compression ignition concept to the American public. The first OK diesel models appeared with little fanfare in 1953, more or less concurrently with the advent of the competing McCoy .049 DuroGlo diesel model. Interestingly enough, neither of the original OK offerings had the same displacements as the far better-known .049 and .075 cuin. models which came later. Those initial offerings had displacements of 0.061 and 0.149 cuin. respectively. They seem to have been introduced very quietly on a trial basis, being sold in very limited numbers mainly in the established diesel territories of Europe and South America. Surviving examples are extremely rare today.
These models were soon replaced by the familiar .049 and .075 cuin. models which are illustrated here. These light, compact and well-made little engines were notable for the very ingenious "shock absorber" system which was built into their cylinder assemblies in an effort to minimize shock loadings on the working parts during operation. They also featured contra-pistons which sealed with O-rings. Once one got used to the feel of this system, the engines started and ran very well indeed by contemporary standards. Despite this, they did not find lasting favor with the American public, being phased out during the latter half of the 1950's.
The full story of the OK diesels may be found on Ron Chernich's "Model Engine News" (MEN) web-site.