'S' Series Sunbeams were produced from 1946 until 1956 when all Sunbeam motorcycle production Stopped.
BSA did however use the Sunbeam name on a couple of scooters in 1959... a sad end to an historic heritage.
During all this time the Sunbeam bicycles continued production and the Sunbeam Cycle rights were sold to Raleigh in 1956/7 who now also own the rights to BSA Cycles.
The S' Series Sunbeams were the only shaft drive Sunbeam motorcycles and were sold as the S7, the S7 deluxe and the S8. Sunbeam's were not produced at BSA's mighty Small Heath factory but at BSA Redditch where they were also designed.

The S7 was designed by Erling Poppe with the first complete prototypes made in 1945.
This followed examination of two captured German motorcycles, a DKW R125 which was almost exactly copied and became the BSA Bantam, and a BMW R75, however it was felt that this was too German looking and that due to bad feeling after the war that it would not sell.
The motorcycle that was designed instead shared the shaft drive of the BMW and the heavy wheels and forks but instead of a flat twin opposed across the frame layout, a new in-line (with the frame) OHC, parallel twin was designed with a top speed in excess of 90 mph.
These bikes did not have the rubber mounted engines of the production models and early production test reports stated that the vibration made the bikes unfit for the purpose. However Sunbeam still sold these early versions and had to recall them all to retro fit the new engine mounts.

Believe it or not BSA originally planned three models based on this engine concept... The S7 'Tourer', The 'Sports' and a rigid 'Trials' version. The S7 'Tourer was said to be good for at least 75mph whereas the 'Sports' with high compression pistons and sports camshaft gave 94 mph.
Unfortunately the 'Trials' and 'Sports' were never put into production probably due to either unsafe handling at speed or high wear rates of the rear drive units.