Triumph launched the first Thunderbird 650 6T in 1950. It was the brainchild of Triumph’s ace engineer Edward Turner, who had a knack for using in-house components to create an exciting new motorcycle.
This 1951 Triumph Thunderbird 650 6T on eBay is a fine example of Turner’s creative re-use skills.
From the Parts Bin
The Thunderbird 650 6T features a 649cc Vertical Twin engine designed by Turner. Instead of building an all-new engine, he took the one from the 500cc Triumph Speed Twin. He bored it out 8mm (from 63mm to 71mm) and lengthened the stroke from 80mm to 82mm.
Triumph’s new bigger Twin had more power and revved higher, cranking out a reported 34 hp @ 6,500 rpm. According to Classic British Motorcycles, the 6T Thunderbird was instantly one of the fastest motorcycles on the market.
Turner used most of the major engine castings from the preexisting 500cc engine, so it fit in the Speed Twin frame. Triumph saved time and money by not having to build a new engine and frame for the 650. But these decisions came with some compromises.
Swingarms and Springs
The Triumph Thunderbird 650 6T has a brazed-lug rigid frame and sprung rear-hub suspension system. Unfortunately, that setup developed a bad reputation. Instead of a conventional swingarm, the 6T Thunderbird has springs running radially between the rear axle and the back hub/spokes/wheel combo.
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It was a workaround devised by Turner, who hoped to give the Thunderbird 650 an inch-and-a-half of travel (1.5 in.) without needing to build a contemporary swingarm. Unfortunately, the springs didn’t absorb bumps well, and the hub would get off-kilter. That led to sketchy wheel movement and compromised handling.
Triumph finally switched to a swingarm arrangement in 1954. The seller of this Thunderbird says the 71-year-old motorcycle is a restored original bike.
The Tank as Centerpiece
Thanks to its top-notch restoration, this 1951 Triumph Thunderbird 650 6T deserves to be taken out regularly on weekends and special occasions. The motorcycle’s headlight nacelle was a contemporary accessory back in its day—housing not only the headlight but also gauges and handlebar mounts.
The housing is a British innovation. Triumph aimed to make cleaning easier in the battle against inclement British weather. The housing design integrates smoothly into the fork, setting the tone for the motorcycle’s centerpiece: its gorgeous blue tank.
Triumph designed the Thunderbird’s full fenders with wet British weather in mind. But they also provide an ample palette for the motorcycle’s signature “Polychromatic Blue” paint.
Ride Like Marlon
A Triumph Thunderbird 6T similar to this one played a role in one of the most iconic motorcycle movie photos of all time. The shot shows Marlon Brando in a black leather jacket, rolled up jeans, and black boots leaning up against a bike in the movie The Wild Ones. That became the iconic bad-boy biker look.
Brando used his own 1950 Triumph Thunderbird 6T in the movie. Ownership of this 1951 6T might not make you as bold as the leader of the Black Rebels Motorcycle Gang. But your street cred will undoubtedly rise with the crew of your local vintage motorcycle club.
