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


Check out these TRIUMPH BOOKS




2018 Classic Triumph Calendar


Triumph Motorcycles: The art of the motorcycle


The Complete Book of Classic and Modern Triumph Motorcycles 1937-Today (Complete Book Series)


Triumph Motorcycles: From Speed-Twin to Bonneville


Triumph Bonneville and TR6 Motorcycle Restoration Guide: 1956-83


British Motorcycles Triumph (Little Books)


Triumph Motorcycles in America


McQueen's Motorcycles: Racing and Riding with the King of Cool


Triumph Motorcycle Restoration


Illustrated Triumph Motorcycles Buyer's Guide: From 1945 Through the Latest Models (Illustrated Buyer's Guide)


Tales of Triumph Motorcycles and the Meriden Factory


Hinckley Triumphs: The First Generation (Crowood Motoclassic)

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Last updated 12/6/17

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