1950 Triumph Thunderbird


1950 TRIUMPH THUNDERBIRD - BIRTH OF THE THUNDERBIRD
The 1950 Triumph Thunderbird was not only the first Thunderbird, it was the first Triumph 650 & it began 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.
1950 TRIUMPH THUNDERBIRD - A STROKE OF GENIUS
He had another brilliant idea as well. As the quest for ever more power had pushed the 500cc Triumph Speed Twin to its limits, Turner simply expanded those limits. He bored it out to 71mm & stroked it out to 82mm & in doing so, created a 649cc fire-breather. The 6T Thunderbird was born & was instantly one of the fastest motorcycles on the market!

1950 TRIUMPH THUNDERBIRD - OLD IS MADE NEW
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 & 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.

1950 TRIUMPH THUNDERBIRD - FRAME & RUNNING GEAR
These included the brazed-lug rigid frame, the rest of the running gear & the infamous "sprung hub". This was another Edward Turner invention designed to bring some rear suspension travel (however slight) to the Triumph 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 & 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 & erratic handling. But, it remained in service until the swing arm came out in 1954.
1950 TRIUMPH THUNDERBIRD - MORE STRENGTH
To cope with the added power, the 1950 Triumph Thunderbird got a new stronger 3-piece pressed-together crankshaft & 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) & improved shift forks. The clutch received an extra plate (now 5 drive & 6 driven).

1950 TRIUMPH THUNDERBIRD - GEAERING
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 sprocket remained 18-teeth on all twins up to & beyond unit construction in 1963.
1950 TRIUMPH THUNDERBIRD - OTHER CHANGES
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 & 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.

1950 TRIUMPH THUNDERBIRD - ENGINE
For the most part, the new 1950 Triumph Thunderbird 650 engine was the same as the 500cc Triumph Speed Twin it evolved from. The cast iron cylinder block & head were similar, but the 650 head was more generously finned & 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 fuels 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 1950 Triumph Thunderbird past 100mph!

1950 TRIUMPH THUNDERBIRD - THE T-BIRD LOOK
The look of the 1950 Triumph Thunderbird was established early on & followed normal convention for a machine of its type. It had generous fenders, made to cope with wet British riding conditions, & a headlight nacelle housing not only the headlight, but the gauges, top yoke, fork tube tops & 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.)

1950 TRIUMPH THUNDERBIRD - EDWARD TURNER HAD A GIFT
Edward Turner was not just a gifted mechanical engineer, he had a real talent for style & color. Just look what he did for the Triumph line when he arrived from Ariel Motorcycles in 1935. He sparked up sales & 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". It proved to be less than successful. The bike pictured here is actually a 1951 model 6T Thunderbird, as a suitable 1950 photo was not available. So the color is not correct for our study of the 1950 Triumph 6T Thunderbird. As mentioned, it should be Thunder-Blue (a blu-grey), but instead it is the correct color for 1951, Polychromatic Blue. Otherwise, the two model years are virtually identical.

1950 Triumph 6T Thunderbird
SPECIFICATIONS

Engine type

Displacement

Bore & Stroke

Compression

Carburetor

Ignition

Engine output

Primary drive

Primary sprockets

Clutch

Gearbox

Ratios, overall:

1st, bottom

2nd

3rd

4th, top

Final drive

Final drive sprockets

Frame Type

Suspension, front

Suspension, rear

Brake, front

Brake, rear

Tire, front

Tire, rear

Wheelbase

Seat Height

Ground Clearance

Fuel capacity

Dry weight

Air-cooled OHV vertical twin, non-unit

649cc / 40.0 ci

71mm X 82mm / 2.79" X 3.23"

8.5:1 (US & export); 7.0:1 (UK)

1- Amal Monobloc, 1"

Lucas magneto

34 bhp @ 6500 rpm

1/2" X .335" X 5/16" chain, 70 links

24T X 43T

Multi-plate, wet

4-speed constant mesh, right foot shift


11.9:1

8.25:1

5.81:1

4.88

5/8" X .400" X 3/8" chain, 101 links

18T X 46T

Brazed lug, rigid

Telescopic fork, hydraulic damping

Sprung rear hub, rigid frame

7" SLS drum

7" SLS drum

3.25" X 19"

3.50" X 19"

55.25" / 140.3 cm

31" / 77.5 cm

5" / 12.7 cm

3 Imp gal (US); 4 Imp gal (UK & export)

370 lbs / 168 kg


MORE THUNDERBIRD PAGES:
Triumph 6T Thunderbird
.....Pre-Unit Thunderbird
.....1950
.....1951
.....1952
.....1953
.....1954
.....1955
.....1956
.....1957
.....1958
.....1959
.....1960
.....Unit-Construction Triumph Thunderbird
.....1963
MORE TRIUMPHS:
Triumph T120 & T140 Bonneville
Triumph TR6
Triumph TR7
Triumph T110 & T110 Tiger
Triumph 6T Thunderbird
Triumph 5T Speed Twin
Triumph T150 & T160 Trident
Triumph X-75 Hurricane


Check out these TRIUMPH BOOKS

COMPLETE BOOK OF CLASSIC & MODERN TRIUMPHS


TRIUMPH MOTORCYCLES IN AMERICA


TRIUMPH MOTORCYCLE RESTORATION


TRIUMPH MOTORCYCLE RESTORATION, PRE-UNIT


TRIUMPH BONNEVILLE & TR6 RESTORATION GUIDE: 1956-1983


TALES OF TRIUMPH MOTORCYCLES & THE MERIDEN FACTORY


TRIUMPH 650 & 750 TWINS OWNERS WORKSHOP MANUAL, 1963-1983


TRIUMPH BONNEVILLE: ESSENTIAL BUYER’S GUIDE


TRIUMPH BONNEVILLE: PORTRAIT OF A LEGEND


ILLUSTRATED TRIUMPH BUYER’S GUIDE, by Roy Bacon


TRIUMPH BONNEVILLE, 2001-2015


TRIUMPH: PRODUCTION TESTERS TALES FROM MERIDEN


TRIUMPH MOTORCYCLE RESTORATION GUIDE


TRIUMPH OWNERS HANDBOOK, UNIT-CONSTRUCTION 350 & 500, Kindle


TRIUMPH ILLUSTRATED WORKSHOP MANUAL 1945-1955, by Clymer


TRIUMPH TWINS & TRIPLES


FACTORY-ORIGINAL TRIUMPH TWINS, 1938-1962


TRIUMPH BONNEVILLE & TR6, by Timothy Remus


TRIUMPH MOTORCYCLES: FROM SPEED TWIN TO BONNEVILLE


TRIUMPH MOTORCYCLES: THEIR RENAISSANCE & THE HINKLEY FACTORY


TRIUMPH PRE-UNIT TWINS OWNERS WORKSHOP MANUAL


TRIUMPH THRUXTON BONNEVILLE 1959-1969


TRIUMPH MOTORCYCLES ILLUSTRATED WORKSHOP MANUAL 1937-1951, by Clymer


TURNER’S TRIUMPHS: EDWARD TURNER & HIS TRIUMPHS


TRIUMPH TWIN RESTORATION, by Roy Bacon


TRIUMPH TIGER CUB & TERRIER 1952-1968, Haynes Repair Manual


TRIUMPH 675 DAYTONA & SPEED TRIPLE REPAIR MANUAL 2006-2010, Haynes


CLASSIC MOTORCYCLES: TRIUMPH


TRIUMPH BONNEVILLE YEAR BY YEAR


TRIUMPH TRIPLES


TRIUMPH RACING MOTORCYCLES IN AMERICA


TRIUMPH MOTORCYCLES


TRIUMPH, by Roy Bacon


TRIUMPH 750/900 TRIPLES & 1200 FOURS 1991-1999, Haynes Repair Manual


TRIUMPH TROPHY BIBLE


TRIUMPH DAYTONA, SPEED TRIPLE SPRINT & TIGER: 885/955 1997-2005, Haynes Repair Manual


BSA & TRIUMPH TRIPLES GOLD PORTFOLIO 1968-1976


TRIUMPH TRIDENT OWNERS WORKSHOP MANUAL, by Haynes


TRIUMPH: A CENTURY OF PASSION & POWER


TRIUMPH BONNEVILLE, by Osprey


TRIUMPH TIGER 100 & 110, 1939-1961, by Roy Bacon


TRIUMPH TIGER 100 & DAYTONA


TRIUMPH BONNEVILLE, by Crowood


TRIUMPH by Don Morley


TRIUMPH TRIPLES & FOURS 1991 & 2004


TRIUMPH 350 & 500 1957-1974 ESSENTIAL BUYERS GUIDE


BONNIE: THE DEVELOPMENT OF THE TRIUMPH BONNEVILLE


TRIUMPH SINGLES: EARLY DAYS TO 1974, by Roy Bacon


TRIUMPH: RETURN OF THE LEGEND


TRIUMPH FUEL INJECTED TRIPLES 1997-2000


BOOK OF TRIUMPH TWINS 1968-1969, by Floyd Clymer


THE TRIUMPH STORY: RACING & PRODUCTION MODELS 1902-PRESENT


TRIUMPH 350 & 500 TWINS 1958-1973, Haynes Repair Manual


TRIUMPH BONNEVILLE 2001-=2008 ROAD TEST PORTFOLIO


HINKLEY TRIPLES & FOURS


TRIUMPH PRE-UNIT TWINS


HINKLEY TRIUMPHS: THE FIRST GENERATION


TRIUMPH BONNEVILLE BIBLE: ALL MODELS 1959-1983


TRIUMPH TWENTY-ONE TO DAYTONA: C CLASS 350 & 500 TWINS


ORIGINAL TRIUMPH BONNEVILLE


TRIUMPH 650 & 750 TWINS


TRIUMPH MOTORCYCLES & CUSTOM BIKES


TRIUMPH MOTORCYCLES


TRIUMPH, THE LEGENDS SERIES


TRIUMPH THUNDERBIRD SUPER PROFILE


TRIUMPH SPEED TWIN & THUNDERBIRD BIBLE


TRIUMPH BONNEVILLE T120/T140


TRIUMPH MOTORCYCLES FROM 1950-1983


TRIUMPH & BSA TRIPLES: THE COMPLETE STORY


TRIUMPH THUNDERBIRD, TROPHY & TIGER ESSENTIAL BUYERS GUIDE


TRIUMPH TIGER CUB BIBLE


ROAD RACING HISTORY OF THE TRIUMPH 500 UNIT TWIN


EDWARD TURNER: THE MAN BEHIND THE MOTORCYCLES


SAVE THE BONNEVILLE: THE INSIDE STORY OF THE MERIDEN WORKERS CO-OP


TRIUMPH DAYTONA 1991-2006 ROAD TEST PORTFOLIO


TRIUMPH DAYTONA 2003-2009 ROAD TEST PORTFOLIO


TRIUMPH TIGER 100 / DAYTONA: DEVELOPMENT HISTORY


TRIUMPH, by Daniel Gilpin


BOOK OF TRIUMPH MOTORCYCLES ILLUSTRATED SHOP MANUAL 1935-1939


TRIUMPH: THE RACING STORY


TRIUMPH BONNEVILLE T120 1959-1974, by Roy Bacon


TRIUMPH BONNEVILLE GOLD PORTFOLIO 1959-1983


TRIUMPH TRIDENT SUPER PROFILE


ILLUSTRATED TRIUMPH BUYERS GUIDE, by Roy Bacon






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NEW PAGES
added this month:

1934 BSA Blue Star
Triumph T140W TSS
1955 Matchless G9B
1963 Matchless G12CS
Triumph Daytona
1967 Triumph Daytona
1968 Triumph Daytona
1969 Triumph Daytona
1970 Triumph Daytona
1973 Triumph Daytona
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Triumph Twenty-One
1959 Triumph Twenty-One
1960 Triumph Twenty-One
1961 Triumph Twenty-One
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