This manual covers 650cc twin motorcycles, including iconic models such as the 6T Thunderbird, TR6 Trophy, and T120 Bonneville, with engine numbers DU13375 and up. These air-cooled parallel-twin motorcycles, developed from successful 500cc predecessors, were produced from the early 1950s through the mid-1970s. Known for their robust engineering and performance, the 650cc twins, with their 649cc displacement and typically 45-50 bhp output, became benchmarks in British motorcycle design. Their cultural impact is significant, having achieved success in racing and trials, and becoming symbols of the 1960s and 70s.

This comprehensive collection of three English-language manuals provides detailed guidance for owners, mechanics, and restorers. It encompasses routine maintenance, including oil changes and valve adjustments, as well as in-depth repair procedures for the engine, 4-speed gearbox, clutch, chassis, and electrical systems. The manuals feature extensive exploded views and illustrations for precise parts identification and assembly, alongside troubleshooting tips for common issues like oil leaks and carburetor tuning. This resource is essential for maintaining the performance, reliability, and longevity of these classic motorcycles.