With the “oil-in-frame” Bonneville’s introduction in 1971, the obvious update that remained missing was a more powerful engine. Things changed with the advent of the 1973 Triumph Bonneville. The new T140V Bonneville 750 was initially an air-cooled, overhead-valve parallel twin that displaced 724cc by virtue of boring the cylinders to 75mm. Soon, though, a new 744cc cylinder block—more compact and with stout 10-stud head fixing—was ready. The compression ratio was 8.6:1, and although horsepower wasn’t stated, estimates placed the output in the low 50s and tests showed 110 mph was possible. The five-speed gearbox was still shifted on the right, although in two years it would change over to the left.
The new Bonneville used the front fork and 10-inch Lockheed cast-iron disc brake from T150V Trident, while the two-piston caliper was covered with chrome. Larger chrome fenders were fitted as on the Trident as well. Electric start remained unavailable. In the United States, the 2.5-gallon tank retained the traditional teardrop shape (British-market bikes had a “bread box” tank), and the color scheme was Hi-Fi Vermillion and gold. “These bikes were essentially vintage when new but are fast, fun, and practical to this day,” Cycle World reported in 2015. All contemporary reviewers noted the excellent handling, despite an increase in weight to 390 pounds (dry). Motorcycle Classics has noted that “the revived Bonneville was in some ways the best Bonnie ever.” Despite organizational turmoil, the factory would eventually build about 350 examples weekly. Some 60,000 would be produced by the end of the run in 1983. In the meantime, the T120R Bonneville 650 continued, receiving minor updates.