1950 Triumph Thunderbird

1950 Triumph Thunderbird Background & History

The 1950 Triumph Thunderbird was not only the first Thunderbird, it was the first Triumph 650 and it launched a long legacy that lasted until the demise of Triumph Motorcycles in 1983. It is said that Edward Turner got the idea for the name from a motel he stayed in while visiting the US on business.

He had another brilliant idea as well. As the quest for ever more power had pushed the 500cc Triumph Speed Twin and the T100 Tiger to their limits, Turner simply expanded those limits. He bored the 500 out from 63mm to 71mm and stroked it from 80mm to 82mm and in doing so created a 649cc fire-breather. The 6T Thunderbird was born and was instantaneously one of the fastest motorcycles on the planet!

Improvements Built into the 1950 Triumph Thunderbird

Another huge advantage was that most of the major engine castings remained relatively unchanged from the 500cc units already in production. And of course this meant that it all fit into the same frame as well, saving even more development and tooling costs. Just as he had done back in 1937 with the seminal Triumph Speed Twin, Edward Turner had once again created a game-changing motorcycle out of components already on the shelf.

These included the brazed-lug rigid frame, the rest of the running gear and the infamous “sprung hub”. This was another Edward Turner invention designed to bring some rear suspension travel (however slight) to Triumph’s rigid frame without investing the money needed to replace it with a proper swing arm rear suspension. Essentially it placed springs radially between the rear axle and the hub/spokes/wheel. In theory, the springs would absorb the bumps while keeping everything in line. The problem should be obvious: any play in the system results in uncontrolled wheel movement and erratic handling. But, it remained in service until the swing arm came out in 1954.

1950 Triumph Thunderbird is Beefed Up

To cope with the added power, the 1950 Triumph Thunderbird got a new stronger 3-piece pressed-together crankshaft and the engine cases were beefed up around the main bearings. The oil pump’s capacity was increased by 20%. The gearbox was strengthened with larger pinions, a greater number of teeth (finer pitch) and improved shift forks. The clutch received an extra plate (now 5 drive plates and 6 driven plates).

Primary gearing was raised by replacing the Speed Twin’s 22-tooth engine sprocket with a 24-tooth. Changing the engine sprocket like this is actually the way the factory preferred to change gearing, as the final-drive (front) sprocket remained 18-teeth on all twins up to and beyond unit construction in 1963.

1950 Triumph Thunderbird Improvements

Another interesting feature was the crankshaft shock absorber. Introduced with the 1950 Triumph Thunderbird, it remained in service until the conversion to alternator electrics in 1953, which was now mounted in its place on the left end of the crank, inside the primary cover. This brilliant device decoupled the engine from the primary, linking them through a spring-loaded, cammed interface that allowed a controlled amount of ‘give’, smoothing out harmful vibrations. It is said to have made everything last longer: engines, primary chains, clutches, gearboxes and even final drive chains! When the alternator replaced it, Meriden attempted to do the same job with rubber shock absorbers inside the clutch hub, but it never worked nearly as well.

For the most part, the new Thunderbird 650 engine was the same as the 500cc Triumph Speed Twin it evolved from. The cast iron cylinder block and alloy head were similar, but the 650 head was more generously finned and utilized a copper gasket instead of a ‘spigot’ arrangement, common for the day. The valve train was identical. Home market 650s had a 7:1 compression ratio to cope with the low octane British Pool petrol available at the time. However, export versions (read that US) had 8.5:1 which was enough to boost power to 34hp @ 6500 rpm, enough to push the 370lb Thunderbird past 100mph!

1950 Triumph Thunderbird Styling

The look of the 1950 Triumph Thunderbird was established early on and followed normal convention for a machine of its type. It had generous fenders, made to cope with wet British riding conditions, and a headlight nacelle housing not only the headlight, but the gauges, top yoke, fork tube tops and the center section of the handlebars. All of this weather protection was also supposed to make the bike easier to clean after riding in the rain. They sure were obsessed with riding in the rain, weren’t they? (Well, I guess we can’t all live in California.)

Edward Turner was not just a gifted mechanical engineer, he had a real talent for style and color. Just look what he did for the Triumph line when he arrived from Ariel Motorcycles in 1935. He sparked up sales and did it almost entirely by juicing up the colors on the bikes. For the 1950 Triumph Thunderbird, Turner selected a blue-grey called “Thunder-Blue”. 

1950 Triumph Thunderbird Specifications

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1950 Triumph Thunderbird Books

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More Triumph Thunderbird Pages

1950 Triumph 6T Thunderbird
1951 Triumph 6T Thunderbird
1952 Triumph 6T Thunderbird
1953 Triumph 6T Thunderbird
1954 Triumph 6T Thunderbird
1955 Triumph 6T Thunderbird
1956 Triumph 6T Thunderbird
1957 Triumph 6T Thunderbird
1958 Triumph 6T Thunderbird
1959 Triumph 6T Thunderbird
1960 Triumph 6T Thunderbird
1961 Triumph 6T Thunderbird
1962 Triumph 6T Thunderbird
1963 Triumph 6T Thunderbird
1964 Triumph 6T Thunderbird
1965 Triumph 6T Thunderbird

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