Triumph's First Twin: Triumph 6/1

Triumph’s first production vertical twin was not the Speed Twin; it was Valentine Page’s Triumph 6/1.

| May/June 2013

1935 Triumph 6/1
Claimed power: 25hp @ 4,500rpm
Top speed: 85mph (est.)
Engine: 649cc air-cooled OHV parallel twin, 70mm x 84mm bore and stroke
Weight: 412lb (187kg)

Triumph’s first production vertical twin was not, as many enthusiasts believe, Edward Turner’s epic 1938 Speed Twin; it was, in fact, Valentine Page’s Triumph 6/1. Almost unheard of in the U.S. and rare even in its home country, had it been successful, Page’s Triumph 6/1 could have changed how we look at Triumph twins.  

From 1928 until 1932, Valentine Page and Edward Turner worked together in the drawing office at Ariel motorcycles. Between them, they would design many of the most successful British motorcycles from the late 1920s to the late 1960s. The phenomenal success and influence of Turner’s later Speed Twin, and the relative failure of Page’s 6/1, reminds us that motorcycle design involves a precarious balance between emotion and engineering.

Turner’s four 

By the late 1920s Page was already well-known, both for his work at the London firm of J.A. Prestwich (whose J.A.P. engines were used by many manufacturers, including Brough Superior) and for his range of single-cylinder machines at Ariel. Regarded as a quiet, studious and kindly man, Page was generous with help and advice for his young assistant. Turner — although largely self-taught and without formal qualifications — was employed on the strength of an idea he showed Ariel boss Jack Sangster for a revolutionary 4-cylinder engine design. That design would become the Ariel Square Four. Working with Page, Turner squeezed a unit construction, 500cc prototype Square Four engine into the frame of the existing Ariel 250cc single. Weighing around 280 pounds, the bike performed admirably. Although manufacturing and cost considerations necessitated changes, the production version (now with a separate Burman gearbox and running gear from the 500cc Ariel SG31 Sloper) was the hit of the 1930 Earls Court motorcycle show in London.

While working with the new engine on the test bench, Turner and Page removed the front crankshaft as an experiment. The resultant 250cc vertical twin delivered such smooth power that Page wondered why they were “bothering with a four.” This was, quite possibly, the “eureka” moment for them both — the instant in which, however dimly, the 6/1 and the Speed Twin were first conceived by their respective designers. They tested both 360-degree (pistons rise and fall together) and 180-degree (one piston up, one down) crankshaft designs and concluded there was little difference between the two arrangements, although the 360 worked better with a single carburetor.

The first Triumph twin 

Toward the end of 1932, Page left Ariel to take up a new post at the struggling Triumph factory, where he designed a range of workmanlike but rather uninspiring singles — and one twin, the 6/1.

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