Description
The T120 Bonneville differed from the Tiger T110 in having twin carburettors for increased power. This was not always an advantage: at a time when customers still did much of the maintenance themselves, adjusting the twin carburettors was difficult and many therefore preferred the Tiger T110. Until 120, the first T1959 Bonneville still had the headlight nacelle with integrated speedometer that the other models had and a semi-double cradle frame. From 1960 the machine was fitted with a separate headlight and also a double cradle frame. The first models also had a pre-unit gearbox, which was separate from the engine and which could be slid to tension the primary chain.
Motor
The engine was a transversely mounted, air-cooled parallel twin with a bore of 71 mm, a stroke of 82 mm and a displacement of 649,3 cc. The crankshaft was mounted in ball bearings, but plain bearings were used for the big ends. The machine had a dry-sump lubrication system with the oil tank in the usual place under the seat. The plunger pump was operated by an eccentrically placed pin on the gear of the inlet camshaft, which was located behind the cylinder block. The exhaust camshaft was located in front of it. The exhaust camshaft gear also drove the ignition magneto. The two carburetors had no air filter and until the end of 1960 a shared float chamber. The 6-volt alternator was located on the left end of the crankshaft. The engine produced 46 hp at 6.700 rpm. In 1962, the engine vibrations that were still present were partly remedied by a better balanced crankshaft.
