BSA used a system of letters and numbers for yearly identification of their machines. This information combined with the yearly numbers below should help you .Date your Triumph, BSA, and Norton motorcycle using our complete chart of engine engine support - check your frame and engine for identification numbers..BSA used a system of letters and numbers for yearly identification of their machines. Before you proceed be sure to read the introduction page. INTRODUCTION .Identifying engine and frame numbers, 1969 season onwards. After dating and identifying many thousands of BSA 's we have found that often a bike was built .