The Thorning 2.5 cc FRV diesel was manufactured by Thorning Bensen of Helsingør (in English, Elsinore), Denmark from late 1950 to some indeterminate point in 1951. It was intended as an updated replacement for the earlier 2.5 cc Thorning III sideport model. 

Unfortunately, the Thorning 2.5 model was released prematurely before all of its design bugs had been worked out. The most notable of these issues was the omission of a hard-wearing sleeve for the main bearing, which resulted in rapid premature wear of the plain unbushed bearing in the early examples. The manufacturer quickly took effective remedial action by adding a bushing, but the damage had been done - an unfavourable test of the original variant in the Danish modelling media had already ended its chances of marketplace success despite the fact that the revised examples like that illustrated here were actually perfectly servicable engines. As a result, only some 500 or so examples of the Thorning 2.5 were manufactured before Thorning Bensen abandoned the model engine field for other activities.

Some further details of this engine are incorporated into the separate article on this site relating to the Thorning III diesel.  A full report on the Thorning 2.5 appears separately on this web-site.