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.

Triumph 650 Twin

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.

Photo By Mick Robinson

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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.

Introduced in 1933 as a new model for 1934, the 6/1’s 649cc parallel twin — the engine type that would later become synonymous with the Triumph name — was the first of its kind offered by the marque. Featuring a 360-degree crankshaft, it had the flywheel in the primary case, outboard of the crankcase. The primary drive was by a pair of large helical gears, which meant the engine had to run backward. The massive crankcase contained a 7-pint oil tank and a single, gear-driven camshaft mounted to the rear of the cylinder block.

The cylinder heads were formed from two separate castings and, in an unexpected design throwback to an earlier era, had exposed valve gear. The design featured a single Amal Type 276 carburetor with a small 1-inch bore to promote good gas flow at low engine speeds. Output was a claimed 25 horsepower at 4,500rpm. Interestingly, the engine was offset to the right in the frame. A unitized 4-speed gearbox (with handshift on early models) completed the powertrain. Sturdily constructed and weighing 412 pounds, the 6/1 was primarily suited to sidecar work.

The machine certainly performed well enough on the road. Late in 1933, a 6/1 hitched to a Triumph Gloria sidecar and ridden by Triumph’s sales manager Harry Perry won a silver medal in the International Six Days Trials (missing a gold medal by just five marks because of time lost repairing a damaged front tire). The outfit was then taken to Brooklands, where it covered 500 miles in just 498 minutes, including refueling stops. This earned the factory the coveted Maudes Trophy for endurance that year.

Yet showroom performance was another matter, and the unit sold poorly. In many ways the 6/1 was a typical Page design, durable and dependable, but hardly handsome. Aimed at the sidecar market and meant to replace the traditional big V-twin, the bike arrived just as the sidecar market was in decline. Consumers were opting instead for the first small, inexpensive cars that were coming on the market. Total production is open to question, with estimates ranging from 100 to 600 built over the model’s two-year life span.

What Triumph needed was a bike as beautiful as it was fast, something to capture the hearts — and wallets — of the buying public. The company — and the public — would not have to wait long, as Triumph introduced the exciting and now iconic 500cc Speed Twin in 1937.

Riding the Triumph 6/1 

After the usual routine of tickling the carburetor, the 6/1 I’m fortunate to be riding starts readily, responding to a blip of the throttle, the mufflers giving a healthy bark that shouts “British Twin!”

It is mechanically quiet, even with exposed valve gear, which is not what I expected at all, and the clutch is nicely weighted.

First gear selects easily and the bike moves smartly away from a standstill. The other gears all select nicely, but respond best to an unhurried and deliberate change, especially between second and third. I had been expecting the torque reaction from the backward-running engine to be somehow intrusive, but it’s not at all noticeable and the engine is more than acceptably smooth. The Triumph 6/1 certainly doesn’t lack power. For a machine rapidly approaching 80 years old it is actually something of a revelation, and it must have been exceptional when new. The well-sprung saddle and girder forks isolate the rider from all but the worst bumps — with the large chrome headlamp dancing entertainingly in front of me — and, on smooth roads at least, ride quality is better than I expected. The large wheels help here (19 inches front and rear), riding bumps well with a long, slim front tire contact patch for steering accuracy.

The brakes are standard fare for the time, with the rear providing most of the stopping power and the front a gentle action. The inverted front brake lever takes some getting used to.

Overall, my brief spin on the 6/1 is enjoyable, even allowing for the fact that its rarity makes it a slightly nerve-wracking enterprise, as there are only somewhere between 17 and 25 left, depending on whose figures you choose to believe.

Having ridden a Triumph 6/1, I have to conclude that Page aimed his twin at the wrong buyer. Yet the 6/1 did not sink without a trace. Comparing the specifications of the 6/1 and the later BSA A10, launched in 1949 — which Page had a heavy hand in — it is difficult to refute claims that the A10 is simply a 6/1 with a central flywheel and chain primary drive. It may have taken him a while, but Page got there … eventually. MC 

Read more from Simon Davis about Turner's Twin, the Triumph 5T.