1961 Triumph Bonneville

1961 Triumph Bonneville Background & History

By the time the 1961 Triumph Bonneville was released, the Bonneville was already a bonafide hit in the marketplace. When the 1959 Triumph Bonneville was launched it was the ultimate evolution of Triumph’s line of high-performance twins. This lineage started in 1938 with the game-changing 500cc 5T Speed Twin, the world’s first ‘modern’ vertical twin. Triumph quickly followed it up with a high performance version, the T100 Tiger. World War 2 threw a blanket on things until 1946 and by this time most of the rest of the British motorcycle industry were close to releasing their own 500cc vertical twins. Between 1946 and 1949, BSA, Ariel, Norton, Matchless/AJS and Royal EnfieldRoyal Enfield all released 500cc vertical twins, all in an effort to keep up with Triumph. But they weren’t sitting on its laurels.

The 1961 Triumph Bonneville was a handsome machine.  Note the 2-tone seat.

In 1950, Triumph upped the ante again by boring and stroking it’s 500 twin into the first Triumph 650, the 6T Thunderbird, again catching the entire industry flat-footed, and again they raced to keep up. By 1954 Triumph had a hot rod version of the new 650, the T110 Tiger. This was soon outshined however by the 1956 Triumph TR6 sporting the new alloy ‘Delta Head’ for ever more power. Up to this point, all of these twins had single carburetors feeding both cylinders, and it was this way on the twins built by the competition also.

1961 Triumph Bonneville, left side.

While the idea of putting two carbs on a twin seems like an obvious move today, at the time it was groundbreaking and one again it stunned the market. The twin-carb 1959 Triumph Bonneville took the world by storm and until Norton came out with their 750 Atlas, it was probably the fastest bike on the market. Even if it wasn’t, the reputation and bragging rights that came with that second carb were worth at least as much as any power increase. In fact, it made a 4 horsepower difference over the single-carb TR6, but who cared, right?

This 1961 Triumph Bonneville engine is of non-unit construction, with separate engine and gearbox joined by the primary chain case on the other side of the bike.  Note the lack of air cleaners.

1961 Triumph Bonneville Frame

When the Bonneville launched in 1959 it featured a new single-downtube frame which was supplanted by a new twin-downtube frame called the ‘duplex frame’ in 1960. It looked great but flexed around the steering head under hard cornering. By 1961 Triumph figured out that the duplex frame needed another frame tube running underneath the backbone (hidden by the tank) adding extra structural strength around the steering head. Steering head angle, or rake, was changed to 65-degrees at this time also. Tire sizes were also increased for 1961 with a 4.00 X 18 Dunlop Universal in back riding on a WM3-18 rim.

1961 Triumph Bonneville engine, primary drive side.  Note the Lucas magneto residing behind the cylinder block.

1961 Triumph Bonneville Engine

tarting with Engine #D7727, the 1961 Triumph Bonneville got a new cylinder head casting with vertical pillars between the outer cooling fins, designed to stop high frequency ringing (the unsupported fins vibrated like tuning forks at high RPM). There were improvements made to the transmission (gearbox) including the replacement of plain bushings with needle-roller bearings on the layshaft. The gearbox itself was also anchored more securely in its mounts. The engine sprocket was reduced in size again from 22 teeth to 21 teeth and the gear ratios were juggled to lower the gearing even more, for better acceleration.  A lower-output alternator was introduced because bulbs had been blowing out at high RPMs. A new brake light switch (Type 22B) was fitted also.

This Triumph advertisement shows the 1961 Triumph T120C Bonneville, which was the 'Street Scrambler' or, in modern terms, an 'enduro'.  Note the high side pipes, one on each side.

1961 Triumph Bonneville Model Designations

Starting with the 1961 Triumph Bonneville, a letter was added to the T120 model designation. The T120R was the Road version, also called a Roadster which had low pipes, and the T120C was the Street Scrambler or Off-Road version, which had high side pipes, one on each side. Changes on the bike were minimal, yet a steady process of development and improvement never abated. Each model year had it’s own color scheme, which differed from the Bonneville’s sister-bike, the TR6, which continued to be styled alike throughout their lives, just with different colors each year. The 1961 Triumph Bonneville is finished in Sky Blue on top and Silver Sheen on the bottom, separated by a hand-painted gold pinstripe.

1961 Triumph Bonneville Specifications

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Triumph Bonneville Books

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Other Triumph Bonneville Pages

1959 T120 Bonneville

1960 T120 Bonneville

1961 T120 Bonneville

1962 T120 Bonneville

1963 T120 Bonneville

1964 T120 Bonneville

1965 T120 Bonneville

1966 T120 Bonneville

1967 T120 Bonneville

1968 T120 Bonneville

1969 T120 Bonneville

1970 T120 Bonneville

1971 T120 Bonneville

1972 T120 Bonneville

1973 T140 Bonneville

1974 T140 Bonneville

1975 T140 Bonneville

1976 T140 Bonneville

1977 T140 Bonneville

1977 T140J Silver Jubilee

1978 T140 Bonneville

1979 T140 Bonneville

1980 T140 Bonneville

1981 T140 Bonneville

1982 T140 Bonneville

1983 T140 Bonneville

1983 TSS Bonneville

1983 TSX Bonneville

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