Based on pre-war designs , it used a single cylinder four stroke engine that displaced 348 cc ( 21.2 cu in ) .
The BSA B31 , introduced in 1945 , was the first new model introduced by the company after the Second World War .
Based on pre-war designs , BSA B31 used a single cylinder four stroke engine that displaced 348 cc ( 21.2 cu in ) .
The BSA B31 , introduced in 1945 , was the first new model introduced by the company after the Second World War .