Offered for sale by BRITISH Only Austria Fahrzeughandel GmbH, is this very rare S.O.S (Super Onslow Special) that was `factory` built with a Stevens engine. Len Vale-Onslow had been developing watercooled engines, but the cost of tooling for production was prohibitive so he took a 172cc sportsVilliers engine and adapted the cylinder heads using a specially developed Serk radiator system.

It is unclear from the letter and the logbook that comes with this bike as to whether the engine was a Stevens produced water cooled engine or whether the water cooled system was a modification to a standard Stevens engine that was done by Len V-O. It seems to me that I cant see why Len V-O would buy a standard Stevens engine to convert when there were many other engine manufacturers around, and then maybe the Stevens brothers were developing the now defunct light van engine technology for motorbikes. If so, why didnt they make it themselves ? The issue is further complicated by the description of the bike as being a 500cc. Not a size that was used on the light van which was 600cc. Even more odd is the logbook that comes with the bike states that the engine size is 249cc, and the engine number is RYR 533, not a sequence that was used on Stevens !

Anyway... here it is, a rare machine with a proven history and a Stevens connection, and any thoughts would be most welcome.