Clews started building motocross bikes in his garage. Having no access to BSA works engines, Clews made his own extensive improvements to the standard BSA B50 500 cc engine, obtained by breaking up  B50 MX bikes.
Clews began constructing motocross bikes in his garage, and due to a lack of access to BSA works engines, he made substantial modifications to the standard BSA B50 500 cc engine obtained by dismantling B50 MX motorcycles.