1951 Triumph Speed Twin

1951 TRIUMPH SPEED TWIN BACKGROUND
The Triumph Speed Twin was the world's first 'modern' vertical twin, when it was introduced in 1937 as a 1938 model. Designed by Edward Turner (who also designed the Ariel Square Four), the 500cc 5T Speed Twin was a revelation at the time. Pretty much everyone else was building big single-cylinder machines, who were already approaching their physical limits at around 500cc and 40 horsepower. Vibration was the enemy of these big singles, and the new vertical twin offered a then-radical solution: two smaller pistons, rather than one big one, rising and falling together, firing in opposing order. They were smooth, willing to rev higher and made more power. And because of Turner's design genius, they could be built with the same tooling as the old singles. The secret was no center main bearing. The 360-degree crankshaft had a large central flywheel and the whole thing was supported by just two main bearings, just like the singles. It worked great, and took the world by storm. Suddenly the world's best singles were outclassed, and virtually every other British motorcycle manufacturer rushed to market with their own vertical twins. World War II intervened of course, and none were built again until 1946. By this time, the once game-changing Triumph Speed Twin had already been eclipsed by the Triumph T100 Tiger. Also a 500 twin, and based on the same bike, the Tiger was the hotter version, essentially Triumph's hot new sport bike. This relegated the Speed Twin to second-class status as the 'cooking version' (British parlance for a low-priced commuter special). It only got worse from there. In 1950, Triumph bored and stroked the 500 out to the (649cc) 650 6T Thunderbird, and suddenly the entire 500 model line was in the back seat. In 1953, the Thunderbird too was relegated to commuter status when the hotter 650 Tiger T110 came out. It happened again in 1956 with the introduction of the 650 Triumph TR6, and again in 1959 with the ultimate sport bike of the era, the 650 Bonneville. With each of these steps, the lowly Speed Twin got bumped farther and farther down the food chain. But the 1951 Triumph Speed Twin was still fairly early in this process and as such, was a very desirable motorcycle to own at the time. It was well-built, and while not as fast as the T110 Tiger or the 6T Thunderbird, it was certainly fast enough, and probably faster than most other motorcycles of the day. Speed Twins sported a headlight nacelle and bigger fenders (mudguards) than the sportier Tiger, which would evolve by the late 1950s into the infamous "bathtub" bodywork.

1951 Triumph Speed Twin SPECIFICATIONS

Model Designation

Engine Type

Displacement

Bore & Stroke

Compression ratio

Carburetor

Engine output

Top Speed

Electrical system

Primary drive

Clutch

Gearbox

Final drive

Frame construction

Suspension, front

Suspension, rear

Brake, front

Brake, rear

Wheel, front

Wheel, rear

Wheelbase

Seat height

Ground clearance

Fuel capacity

Weight

Triumph 5T Speed Twin

Air-cooled OHV vertical twin

498cc

63mm X 80mm

7.0:1

one- Amal 15/16"

28 bhp @ 6,000 rpm

85-90 mph

6-volt, Lucas magdyno, 40watt

Chain

Multi-plate, wet

4-speed constant mesh, right-foot shift

Chain

Steel tube, brazed lug

Telescopic

Rigid frame, sprung hub (optional)

7-inch SLS drum

7-inch SLS drum

3.25" X 19.0" Dunlop Universal

3.50" X 19.0" Dunlop Universal

54.0"

29.5"

6.0"

4 Imp gal

361 lbs, dry


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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