The Triumph Twenty One is a British motorcycle

Motorcycle

A motorcycle is a single-track, two-wheeled motor vehicle. Motorcycles vary considerably depending on the task for which they are designed, such as long distance travel, navigating congested urban traffic, cruising, sport and racing, or off-road conditions.Motorcycles are one of the most...

 made by Triumph Engineering Co Ltd in Coventry

Coventry

Coventry is a city and metropolitan borough in the county of West Midlands in England. Coventry is the 9th largest city in England and the 11th largest in the United Kingdom. It is also the second largest city in the English Midlands, after Birmingham, with a population of 300,848, although...

. The Model Twenty One was the first of the Triumph unit construction

Unit construction

Unit construction is a term used to describe the design of larger motorcycles where the engine and gearbox components share a single casing. The term is sometimes applied to the design of automobile engines and was often loosely applied to motorcycles with rather different internal layouts such as...

 twin cylinder motorcycles. Rebranded as the Triumph 3TA in 1959 it continued in production until 1966 when it was replaced by the Triumph T90.

Development

Launched in 1957 the Model Twenty One was the first of the Triumph unit construction

Unit construction

Unit construction is a term used to describe the design of larger motorcycles where the engine and gearbox components share a single casing. The term is sometimes applied to the design of automobile engines and was often loosely applied to motorcycles with rather different internal layouts such as...

 twin cylinder motorcycles from the Meriden

Meriden, West Midlands

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 factory. With a capacity of 349 cc, the engine was a classic Edward Turner

Edward Turner

Edward Turner was a British motorcycle designer. He was born in Camberwell in the London Borough of Southwark, on the day King Edward VII was proclaimed King....

 design with a 360 degree crankshaft, twin gear driven camshafts and twin plunger oil pump. The cylinder block was cast iron with an alloy head and separate rocker boxes. The engine was dry sump lubrication and there was a single Amal Monobloc carburettor. Drive was by a conventional four speed gearbox, with a right hand gear lever.

There are two explanations for the 'Twenty One' name spelt out in full on the side panels. The first explanation is that it celebrates the twenty-first anniversary of Triumph Engineering Co Ltd. The second explanation is that the important US export market rated motorcycle engine displacement

Engine displacement

Engine displacement is the volume swept by all the pistons inside the cylinders of an internal combustion engine in a single movement from top dead centre to bottom dead centre . It is commonly specified in cubic centimeters , litres , or cubic inches...

in cubic inches and 21 cubic inches equates to 350 cc.

In 1959 the Twenty One was rebranded the Triumph 3TA and also produced as a 500 cc version, the Triumph 5TA, which was also referred to as the 'new Speed Twin'. The 'A' designation was a reference to the fact that both motorcycles were fitted with an alternator as standard, as the pre-unit models had been fitted with a Dynamo. The original versions of both the 350 cc and 500 cc models had the fully enclosed rear end which was fashionable in the late 1950s. It was not popular with American customers, where the extra weather protection was less important however, and it got called the 'bathtub'. They also found that the extra sheet metal made access for servicing more complicated.

The 3TA and the 5TA both continued in production until 1966 when were succeeded by the T90 and T100 respectively.