The Elfin ball-race models were manufactured by Aerol Engineering of Liverpool, England. They were introduced in late 1954, remaining on the market until the final cessation of all Aerol production in late 1957. The basic design was offered in three different displacement categories - 1.5 cc, 1.8 cc and 2.5 cc. Each of these models appeared in several distinct variants.
The Elfin ball-race engines were refreshingly out-of-the-rut designs, featuring reed valve induction along with a highly unusual crankcase configuration. However, they suffered from wide fluctuations in the precision of fit and finish applied to their working components. A good one was really good, but many of them failed to meet that standard. This was mainly due to Aerol Engineering's ongoing dependence upon clapped-out wartime surplus machine tooling which they could not afford to replace. It was in fact this issue which led to the winding-up of Aerol Engineering in late 1957.
Full details of the Elfin ball-race models may be found in my earlier article on Ron Chernich's "Model Engine News" (MEN) web-site.