1973 Triumph Bonneville 650 T120

Make Model	Triumph Bonneville 650 T120
Year	1973
Engine	Four stroke, parallel twin, OHV
Capacity	649 cc / 39.6 cu in
Bore x Stroke	71 x 82 mm
Compression Ratio	9.0:1
Cooling System	Air cooled
Induction	2 x 30 mm Amal concentric carburetors
Ignition	Battery, coil
Starting	Kick
Lighting system	12V alternator
Oil system.	Double plunger pump, dry sump
Oil capacity	3.4 L / 7.2 US pt / 6 Imp pt
Clutch	Multi-disc, wet
Max Power	37.3 kW / 50 hp @ 7000 rpm
Max Toque	52.1 Nm / 5.3 kgf-m / 38.5 lb-ft @ 6000 rpm
Transmission	4 Speed
Final Drive	Chain
Gear Ratios	4th 4.95 / 3rd 6.14 / 2nd 8.36 / 1st 12.08
Front Suspension	Telescopic forks
Rear Suspension	Swinging arm, dual shocks
Front Brakes	Drum
Rear Brakes	Drum
Front Tyre	3.25 -19
Rear Tyre	4.00 -18
Fuel Capacity	16L / 4.2 US gal / 3.5 Imp gal
Wet Weight	181 kg / 399 lbs

The 1971 Triumph Bonneville was the problem child of a shotgun marriage. It was responsible for Triumph missing that year’s U.S. sales season, and it just about bankrupted the company.

The late Sixties Triumph Bonnevilles were, and still are, considered to be the best of the lot. But a major program of standardization was underway across the BSA Group, which also owned Triumph. For the 1971 season, BSA planned to use a new oil-bearing frame for both BSA and Triumph 650 twins.

However, the new Triumph frame had been designed around the BSA 650 engine, and when the first batches of frames were delivered to Triumph’s Meriden factory, assembly line workers found they couldn’t fit the Triumph engine in the frame without removing the rocker boxes from the cylinder head first.

The 1971 Bonnies were already behind schedule because of production delays caused by a shortage of parts — the result of teething troubles with a new computer system. The cumulative result was that very few Bonnevilles were at U.S. dealers for the critical April to June sales season. Other problems with the 1971 bike included a seat height only suitable for people over 6 feet tall, major frame failures caused by the center stand being mounted on the oil-bearing “sump,” and aesthetics only a short-sighted mother could love. The 1971 model is perhaps the least popular of all Bonnies.