Triumph Bonneville
Pre-Unit Construction
1959-1962

WHAT IS A TRIUMPH BONNEVILLE PRE-UNIT?

UNIT VS. PRE-UNIT
The Triumph T120 Bonneville was a 649cc vertical twin, based on existing 650 Triumph twins, T110 and TR6, but with a twin-carb head and an extra carburetor. Pre-Unit Construction refers to any 650 twin built through the 1962 model year, because in 1963, Triumph came out with a new "Unit-Construction" engine. Pre-Unit, or Non-Unit Construction means that the Engine Crankcase, the Primary Case and the Gearbox are all separate components which are bolted together with brackets, in the frame. In the case of Pre-Unit Triumphs, and many other Classic British Motorcycles, the gearbox was actually rotated in it's mounts as the only means of adjusting the primary chain. Once the primary was adjusted, the final drive chain then needed to be readjusted. Non-Unit Construction was adopted by nearly every British bike maker as well as Harley-Davidson. Most position the final drive sprocket between the gearbox and the clutch, sandwiched behind the primary drive. This was done to keep the whole package rigid.

BENEFITS OF UNIT CONSTRUCTION
In 1963, Triumph introduced their 'Unit Construction' engine, which incorporated the Engine, Primary and Gearbox all in one unitized housing. The cast aluminum case split vertically into two halves, with the inner primary case going with the left crankcase half, and the gearbox housing going with the right. The result was an engine that was lighter, stronger, more modern and cleaner than the Pre-Unit engine it replaced. And it made it possible to pull even more power out as the 1960s progressed. With all this, the age of the Pre-Unit Triumph was over, the 500 twin already gone unit-construction in 1959.


Triumph Bonneville Pre-Unit
YEAR-BY-YEAR


1959 TRIUMPH BONNEVILLE
650cc: T120
First-year Bonnie stuck 2 carbs on new Delta Head for more power. Old frame, clunky T-bird styling, wild tangerine paint job & late release, but still a hit!


650cc: T120A (Road)
650cc: T120B (Scrambler)

1960 TRIUMPH BONNEVILLE
Second-year Bonnie is practically a new bike, with new 'duplex frame', new styling (more like the TR6) & more conventional blue color scheme.



1961 TRIUMPH BONNEVILLE
650cc: T120C (Scrambler)
650cc: T120R (Road)
Third-year of Triumph Bonneville pre-unit production. Amal Monobloc carbs w/integral float bowls replace remote float bowl. Fastest motorcycle on the market.


1962 TRIUMPH BONNEVILLE
650cc: T120C (Scrambler)
650cc: T120R (Road)

Last year of the Triumph Bonneville Pre-Unit, before the switch to Unit Construction. Mostly carry-over from previous model year.


NEW VIDEO:
"TRIUMPH BONNEVILLE THRU THE YEARS"

Take a video walk through every year of classic Triumph Bonneville, from 1959 to 1983. All are taken from the same camera angle to provide some continuity.


MORE TRIUMPH BONNEVILLES:
Triumph Bonneville
Triumph Bonneville Pre-Unit (1959-1962)
.....1959
.....1960
.....1961
.....1962
Triumph Bonneville, Unit-Construction(1963-1970)
.....1963
.....1964
.....1965
.....1966
.....1967
.....1968
.....1969
.....1970
Triumph Bonneville, Oil-in-Frame
.....1971
.....1972
.....1973
.....1974
.....1975
.....1976
.....1977
.....1978
.....1979
.....1980
.....1981
.....1982
.....1983
Les Harris Bonnevilles(1983-1989)
OTHER TRIUMPHS:
Triumph TR6
Triumph TR7
Triumph Trophy
Triumph Tiger
Triumph Thunderbird
Triumph Trident
Triumph X-75 Hurricane


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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


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BSA & TRIUMPH TRIPLES GOLD PORTFOLIO 1968-1976


TRIUMPH TRIDENT OWNERS WORKSHOP MANUAL, by Haynes


TRIUMPH: A CENTURY OF PASSION & POWER


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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


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TRIUMPH PRE-UNIT TWINS


HINKLEY TRIUMPHS: THE FIRST GENERATION


TRIUMPH BONNEVILLE BIBLE: ALL MODELS 1959-1983


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ORIGINAL TRIUMPH BONNEVILLE


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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


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TRIUMPH DAYTONA 2003-2009 ROAD TEST PORTFOLIO


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ILLUSTRATED TRIUMPH BUYERS GUIDE, by Roy Bacon






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