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In 1951, Allbon introduced their Dart and set a fashion for half-cc diesels in England. The Elfin 50 was announced shortly after the Dart, althought its actual entry into the marketplace was delayed until early 1952. Elfin favoured under-square engines, and this one follows that trend. The measured bore and stroke of this example are 8.36mm x 9.78mm, giving a calculated displacement of 0.54 cc, a little above the nominal capacity, just like the similar-sized 0.55 cc Dart. This capacity was later repeated in the AS-55. The Frog 50 really was a 0.5cc diesel, and the ED Baby was fractionally smaller at 0.46cc.
The marketplace success of the engine was not great and it quietly faded away early on—making it a highly prized and priced item in collections today. It's lack of wide acceptance was definitely not due to any shortfall in performance—the engine certainly starts and runs with the best of them! The general layout with the under-slung tank forces the engine to be mounted in an upright position if the supplied tank is to be used. It is possible that the engine’s relative bulk and inconvenient layout for other mounting positions as well as for control line played a part in its relative lack of popularity.
A strong Arden design influence is very obvious—apart from the porting, the updraft intake and under-slung tank are very reminiscent of the Arden layout, as is the radial mount with screw-in backplate. The latter feature had also been adopted earlier by Kemp for their Hawk Mk. III.
Elfin 50 and Allbon Dart