Development
Although designed in the mid-1960s, the BSA Rocket3 / Triumph Trident engine had its origins in a 1938 parallel twin, the 500 cc Triumph Speed Twin of 1937 designed by Edward Turner. The 1938 Tiger 100 was a sports version of the Speed Twin, and in essence the Trident three-cylinder engine is a “Tiger 100 and a half” (although the triple has a longer stroke than the "squarer" Tiger 100 engine). Following Triumph tradition, the OHV Trident engine has separate camshafts for inlet and exhaust valves.
The three-cylinder design was started in 1962 by Bert Hopwood and Doug Hele. Meanwhile, test engineers developed the handling of the chassis by affixing lead weights onto a standard 650 Bonneville. The first prototype, P1, was running by 1965, and it seemed that Triumph might have a machine in production by 1967. However, the decision to produce a BSA version with sloping cylinders and to employ Ogle Design to give the early Tridents / Rocket 3s their 'square tank' look not only robbed the prototype of its lean looks and added 40 lb (18 kg) of weight, but also delayed production by 18 months. During 1966, a P2 prototype was produced with a more production-based Trident engine, with changed bore and stroke dimensions and improved cooling. Ultimately, Hele obtained 90 bhp (67 kW) from a Trident engine, leading to speculation that if development had sped up in 1964, a 140 mph (230 km/h) British superbike could have been a reality in 1972.
Although most British motorcycles used a wet multiplate clutch, this triple had a dry single-plate clutch sited in a housing between the primary chaincase and the gearbox. Mounted on the end of the gearbox mainshaft where one might expect to find the clutch there was instead a large transmission shock-absorber.
All the three-cylinder engines, and the Rocket 3 motorcycles, were produced at BSA’s Small Heath site, but final assembly of the Triumph Trident model was carried out at Meriden in Coventry. The major differences were the engine and frame: The BSA had an A65-style double-loop cradle frame (with engine mounted at a slant), while the Triumph had a Bonneville-style single downtube frame with vertical cylinders. Other differences were cosmetic. Triumphs sold better in the US despite BSA’s Daytona racing successes of the early 70s. However sales did not meet expectations, and for the 1971 model year a fifth gear was added, creating the models BSA A75RV and Triumph T150V. BSA were having financial difficulties, and only some 205 five-speed Rocket 3s were built before production of the BSA variant ceased. Production of the five-speed Triumph T150V (with a front disc brake replacing the original drum) continued until 1974. For the 1975 model year the Trident was updated to the T160.
Read more about this topic: BSA Rocket 3/Triumph Trident
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