Triumph Bonneville: Meriden T120 and T140 (1959 to 1983) and Hinckley Bonneville (2001 onwards)

The Bonneville is the best-known British motorcycle. Triumph launched the 650cc T120 for 1959, named after the Utah salt flats where Triumph-engined streamliners had set speed records, and it became the definitive British sporting twin of the 1960s, especially in the United States. Built at Meriden near Coventry, it moved from a pre-unit engine and separate gearbox to unit construction for 1963, then into the controversial oil-in-frame chassis for 1971.

The 750cc T140 followed in 1973. It was intended as a stopgap, but after the BSA group collapsed the workers' co-operative at Meriden kept it in production until early 1983, adding a left-foot gearchange, disc brakes, electronic ignition and electric start along the way. A small run was then built under licence in Devon.

John Bloor's new Triumph company at Hinckley revived the name with an air-cooled 790cc parallel twin that went on sale in 2001, and the range has continued since, with water-cooled engines from 2016. These bikes share the look of the originals but are modern, reliable machines.

The Meriden Bonneville is light and quick-steering, with lively performance but notable vibration and oil-tightness that depends on its last rebuild. Parts support is excellent. The biggest questions for a buyer at a static sale are originality, identity, the state of the engine and the quality of any restoration, particularly on bikes repatriated from the USA.

• T120: 1959 to 1972 (Motorcycle Classics). 649cc ohv parallel twin with twin carburettors. Claimed power about 46hp in 1959 and 52hp for 1963 to 1970.
• T120 frames: a duplex frame for 1960, a single-downtube frame with the unit-construction engine from 1963, and the oil-in-frame chassis from 1971.
• T120 gearbox: four-speed with right-foot change, separate from the engine until 1962.
• T140: 1973 to January 1983 at Meriden (Classic Bike Guide). First 724cc, then 744cc within months, with a five-speed gearbox and front disc brake (Classic Bike).
• Harris Bonneville: built under licence at Newton Abbot, Devon, 1985 to 1988; Wikipedia gives 1,300 completed.
• Hinckley Bonneville: Bennetts gives the 790cc air-cooled twin from 2001; MCN and Triumph's own press material date its unveiling to 2000. Fuel injection and 865cc for all models from 2008.
• Water-cooled range: 1200cc T120 introduced for 2016 (MCN).
• Production totals: no reliable overall figures were found. Wikipedia gives 2,400 T140J Silver Jubilee and 250 Royal Wedding bikes.

Meriden T120 and T140

• 1959: Tiger 110 based, with headlamp nacelle and magneto ignition.
• 1960: duplex frame and alternator. Motorcycle Classics says the early duplex frame could crack below the steering head, and a brace was added during the year.
• 1963: unit-construction engine, coil ignition.
• 1966: 12 volt electrics.
• 1968 to 1970: twin-leading-shoe front brake; often seen as the best-developed T120s.
• 1971 to 1972: oil-in-frame chassis with a tall seat at first, revised during 1972.
• 1973: T140V 750 with five speeds and front disc.
• 1976: left-foot gearchange and rear disc. About 1,500 right-foot 750s were built in 1975 (Classic Bike Guide).
• 1977: T140J Silver Jubilee.
• 1978 to 1979: T140E with emissions-compliant head; Classic Bike notes electronic ignition and a different carburettor choke arrangement from 1979.
• 1980: T140ES electric start. Other late variants include the Executive touring model and the black and gold US-market T140D.
• 1981: Royal Wedding edition. 1982: eight-valve TSS and the US-styled TSX.

Hinckley

• 2001: 790cc Bonneville, with T100 from 2002 and the black-engined SE from 2003.
• 2006 to 2008: 865cc engine, first on some variants, then all models with fuel injection in 2008.
• 2009: cast wheels on the base model.
• 2016: water-cooled T120 1200.

Frame and cycle parts

• Pre-unit 1960 duplex frames: check below the headstock for cracks or repairs.
• Oil-in-frame bikes: look for leaks and cracks around the centre stand mounts. A Classic Bike restorer reports frames cracking at the bottom of the oil reservoir are rare in his experience.
• Check wheels, chrome rims and spokes, fork seals and tyre age. Old tyres on stored bikes are often cracked.
• Hinckley: check for corroded fasteners and spokes, flaking engine paint and sticking front caliper sliders.

Engine

• Meriden twins use oil, and Classic Bike Guide suggests about a pint every 200 miles is normal. Look for serious leaks, especially from the pushrod tubes, which need a top-end strip.
• With permission, check the oil returns to the tank after start-up. The oil light should go out quickly. A missing crankshaft seal in the timing cover leaves the bottom end without pressure.
• Some smoke on the side stand is normal and should clear when the bike is upright.
• Bottom ends are generally strong; top ends are more often rebuilt.
• TSS eight-valve heads were porous when new and leaked oil.
• Hinckley: look for smoke on start-up and check the oil pressure warning light, as sensors fail.

Gearbox and transmission

• Check all gears select. Water can enter the gearbox along the clutch cable if the bike stood outside.
• Clutches should neither slip nor drag; a clutch stuck after standing usually frees off.
• Hinckley: check for clean downshifts on well-used bikes.

Brakes and suspension

• Motorcycle Classics notes many owners find the T120's drum brakes weaker than period tests suggested. On the T140, Classic Bike rates the 1979-on twin front disc and rear disc as the best arrangement.
• Hinckley owners commonly report soft standard suspension and corrosion on brightwork.

Electrics

• Meriden looms deteriorate with age. Ask whether the bike has a new loom, electronic ignition or a modern regulator and rectifier.
• Hinckley: water at the wiring junction beside the tank and failed coils, switchgear and earths are common faults.

Identity and paperwork

• Check that engine and frame numbers match each other and the V5C, and that they suit the claimed year and model.
• Many Bonnevilles were repatriated from the USA. Real Classic warns that a restored-looking import may still need a full engine rebuild.
• Special editions such as the Jubilee, Royal Wedding, TSS and Executive are worth verifying with the club.
• The Triumph Owners Motor Cycle Club is accredited by DVLA to issue certificates of age, including for imported bikes never registered in the UK.
• GOV.UK states that machines built before 1 January 1986 can use the historic tax class from April 2026. Early Hinckley bikes do not yet qualify.

Parts supply for Meriden Bonnevilles is described by Classic Bike as unrivalled, with almost every component available new. Many independent specialists rebuild engines and restore bikes, and Hinckley models are served by Triumph dealers as well as independents. The Triumph Owners Motor Cycle Club (https://tomcc.org), founded in 1949, offers a dating service, archives of factory records and a members' forum.

• Do the engine and frame numbers match each other, the V5C and the claimed model?
• Is the bike a UK machine or a US import, and when was the engine last rebuilt?
• Has the oil system been checked, including the timing cover crank seal and filters?
• What electrical upgrades have been made, and is the loom new or original?
• How long has the bike stood, and has the fuel system been cleaned?