Triumph 650 GT Thunderbird

Triumph’s 650 Thunderbird, first launched in 1949, is probably the single machine best known to the post-war generation. For this was the bike ridden so defiantly by Marlon Brando in the 1952 film “The Wild One” (‘ What are you rebelling against, Johnny?’ ‘Whadd’ya got?’).

The T-bird also linked two eras. Its engine was the first substantial development of Edward Turner’s famous Speed Twin design of 1937 – the machine which was to make parallel twins the mainstay of motorcycle design for over 30 years. Later , even Japan’s first attempts at entering the big bike market aped the British layout; Kawasaki ‘s 650cc twin was a near-copy of BSA’s A65, although Yamaha’s XS1 boasted one overhead camshaft, whilst Honda ‘s CB450 was the first roadster with two.

Specifications

Engine

Horsepower

transmission

Frame

Brakes

top Speed

Years in Production

air-cooled 649cc parallel twin

34 bhp @ 6300 rpm

4-speed

tubular twin cradle

drum / drum

103 mph

1949-1966

Yet in pumping out the twin from 500 to 650cc, Turner believed this to be the limit for the design if vibration was not to become excessive. Later 750cc versions (not to mention Norton’s 850 Commando), would probably have surprised him. Most riders agree, however, that 650cc was the ideal compromise between smoothness and power.

Although nominally a post-war machine, the T-bird arrived at a time of austerity in Britain, with rationing still in force. The same constraints affected motorcycle manufacturing, although Triumph began the period with a victory for Ernie Lyons on a Tiger 100, the sports version of the 500cc Speed Twin. The Thunderbird itself was launched with an impressive publicity stunt. Three machines were ridden to the French race track at Montlhery, put through 500 laps at an average of 90mph (with flying laps at over I00mph), then ridden home again. One such machine resides in the Beaulieu motorcycle museum.

In essence the early T-bird was identical to the contemporary Speed Twin, itself substantially a pre­ war design, other than the extra 150cc and a change of colour. The air-cooled engine is separate from the gearbox, linked by an enclosed single-row chain. Valve actuation is by push rods from paired camshafts fore and aft of the crankcase mouth.

Rear suspension was by Triumph’s ubiquitous sprung hub, for the rear swinging fork had barely arrived. Oil-damped telescopic forks of Triumph design had first replaced girder suspension on the 1946 Speed Twin. Overall, the Thunderbird was a lighter machine than most in its class, with the lively acceleration typical of the mar que.

The extra capacity, though, was vital. Consumers, particularly in America, were increasingly demanding more power, and the 650 supplied it in becoming perhaps the first affordable ‘ton up’ machine. For Triumph, additional costs were modest, and even in the shops the difference between 500 and 650cc was a mere £10, the T-bird costing just £194 when introduced. Other British manufacturers soon followed suit.

When launched, the T-bird was almost in a performance class of its own, an d certainly nothing could come near it at the price. In the USA, this frightened Harley-Davidson so much they went to astonishing (but unsuccessful) lengths to thwart Triumph sales. Yet just as the Tiger 100 had evolved as the high- performance version of the Speed Twin, so the need was clear for an even hotter version of the T -bird .

The result was first the Tiger 110 of 1954, then the legendary Bonneville 120. Development of the T-bird continued, adding swing-arm rear suspension, light alloy cylinder heads, more power (37bhp by 1960), better brakes and, in 1963, unit construction. By then the controversial ‘bathtub’ rear bodywork had been largely accepted, as the original concept gave way to a handsome, more civilised touring design. But even 46 years on, the evocative legacy of the Thunderbird name lingers on, in the 900cc triple of born-again Triumph.

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