Triumph Bonneville T120 & T140

TRIUMPH BONNEVILLE | T120 & T140

The classic Bonneville, from the first 650 T120 through to the later 750 T140.

The Bonneville name first appeared on the T120 for 1959 and stayed at the centre of Triumph's twin-cylinder range through the Meriden years.

This page covers the classic T120 and T140 family, including the main production changes, engine and frame dating, Angloclassics workshop examples, factory manuals and owner resources.

1959-1962 | 650

T120 pre-unit

The first Bonneville used Triumph's 649cc twin with a separate four-speed gearbox. These are the original pre-unit T120s and are quite different in chassis and engine layout from the later unit bikes.

The early styling and mechanical details changed year by year, making correct dating particularly useful on restored examples.

1963-1970 | 650

T120 unit construction

For 1963 the Bonneville moved to Triumph's unit-construction 650 engine, combining the engine and gearbox in one casing. This became the familiar late-1960s Bonneville layout.

Detail changes included brakes, electrics, styling and US-market equipment, but the basic conventional-frame T120 remained recognisable through 1970.

1971-1972 | 650

Oil-in-frame T120 and T120V

The 1971 Bonneville adopted the new oil-in-frame chassis, with the engine oil carried in the frame rather than a separate oil tank. The first version was noticeably tall and the chassis was revised as production continued.

The T120V arrived for 1972 with a five-speed gearbox, while retaining the 649cc engine and the basic oil-in-frame layout.

1973-1978 | 750

T140V

The T140V increased capacity to 744cc and used a five-speed gearbox. Early examples had a hydraulic front disc brake and rear drum, with later production gaining a rear disc and left-foot gear change.

Production was interrupted during the Meriden dispute before the workers' cooperative restarted manufacture in 1975.

1978-1983 | 750

T140E and later Bonnevilles

The T140E brought revised cylinder-head breathing and Amal MkII carburettors. Electronic ignition followed, while electric-start versions appeared as the T140ES from 1980.

The final Meriden years also produced several limited and specialist variants before motorcycle production at the factory came to an end in 1983.

1985-1988 | 750

Harris Bonneville

After Meriden closed, Les Harris built licensed Triumph Bonnevilles in Devon using the 750 twin with updated cycle parts, including equipment from suppliers such as Marzocchi, Brembo and Bosch.

They continue the classic Bonneville line, but sit outside the main Meriden T120 and T140 story covered on this page.

ENGINE, FRAME AND DATE CODES

Identifying and roughly dating a classic Bonneville

Triumph changed its numbering system during the Bonneville's production life. The early pre-unit and unit machines use serial-number ranges, while bikes from the 1969 model year use letter codes for the month and model year.

Factory model years do not always match the calendar year in which a bike was built, so the number system is more useful than relying on a registration date alone.

1969 ONWARD DATE CODES

From the 1969 model year Triumph used two letters with the serial number. The first letter identifies the month of manufacture and the second letter identifies the model year. The engine and frame numbers should correspond on an original matching-numbers bike.

ANGLOCLASSICS WORKSHOP

Bonneville work at Angloclassics

We do not have a large Bonneville sales archive yet, but several customer bikes have been through the workshop. These give a more useful picture of the sort of faults and unfinished work that turn up on motorcycles still being used today.

TRIUMPH OWNERS IN NEW ZEALAND

Triumph Owners Motor Cycle Club NZ

For Bonneville owners in New Zealand, TOMCC NZ is a useful local club with members across the country, including owners of Coventry and Meriden-era Triumphs. The club provides an information network around parts and repairs, local activities and a national rally.

Triumph factory records

The UK Triumph Owners' Motor Cycle Club also maintains surviving factory records and offers a dating service for owners who need a formal check rather than a rough serial-number guide.

PARTS AND FACTORY INFORMATION

Useful Bonneville parts and manuals

Factory workshop manuals and parts books are the better source for procedures, settings and exploded diagrams. Angloclassics also produces an oil-pressure gauge kit for later Triumph and BSA twins.