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Triumph Bonneville 650 T120

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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
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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.