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 started building motocross bikes in his garage. He lacked access to BSA works engines, so he modified the standard BSA B50 500cc engine from dismantled B50 MX motorcycles.