BSA A75 Rocket III

The BSA Rocket 3/Triumph Trident was the last major motorcycle developed by Triumph Engineering at Meriden, West Midlands. It was a 750 cc air-cooled unit construction pushrod triple with four gears and a conventional chassis and suspension. The motorcycle was badge-engineered to be sold under both the Triumph and BSA marques. The Rocket 3/Trident was part of Triumph's plan to extend the model range beyond their 650 cc parallel twins.

Created to meet the demands of the US market, the smooth 750 cc three-cylinder engine had less vibration than the existing 360° twins. Although BSA experienced serious financial difficulties, 27 480 Rocket 3/Tridents were produced during its seven-year history.

Although designed during the mid-1960s, the BSA Rocket 3/Triumph Trident engine originated in a 1937 parallel twin: the 500 cc Triumph Speed Twin, designed by Edward Turner. The 1938 Tiger 100 was a sports version of the Speed Twin; the Trident three-cylinder engine is a larger version (although the triple has a longer stroke than the Tiger 100 engine). Following Triumph tradition, the OHV Trident engine has separate camshafts for the inlet and exhaust valves.

The three-cylinder design was developed in 1962 by Bert Hopwood and Doug Hele. Test engineers developed the chassis' handling characteristics by affixing lead weights on 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 employ Ogle Design to give the early Tridents/Rocket 3s their "square tank" added bulk and 40 lb (18 kg) of weight, delaying production by 18 months.

In 1966 a P2 prototype was produced with a more production-based Trident engine, different bore and stroke dimensions and improved cooling. Hele got 90 bhp (67 kW) from a Trident engine, leading to speculation that if development had quickened in 1964 a 140 mph (230 km/h) British superbike could have been produced by 1972.

Although most British motorcycles used a wet multiplate clutch, this triple had a dry single-plate clutch in a housing between the primary chaincase and the gearbox. Mounted on the end of the gearbox mainshaft (where the clutch would be expected) was 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 during the early 1970s. Sales did not meet expectations; for the 1971 model year a fifth gear was added, creating the 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.