Looking back through the pages of motorcycling's history, it is surprising that the concept of a vertical twin four stroke engine took so long to catch on. Werner produced the first really practical design in 1903. Their design was sufficiently advanced to have the customary automatic inlet valve operating in conjunction with a mechanically operated exhaust valve and a two-throw crankshaft. The latter practice was one that would be adopted by the Japanese some 50 or so ears later, an arrangement that allowed the pistons to rise and fall alternately. Other vertical twin designs followed, but none seemed to catch on, although one must not overlook Alfred Scott's contribution only a year later. On February 11, 1904 he patented his legendary twin cylinder two-stroke engine. It set the pattern for his long-running association with the many different models that bore his name, almost all of which adhered to the same basic engine layout.
Triumph first showed an interest when they announced preliminary details of a four stroke vertical twin engine during August 1913. They intended it to become part of a complete machine once it had been subjected to what they described as 'severe testing'.
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This engine, with a 45 horsepower rating, also had a two-throw crankshaft, with pistons that rose and fell alternately, and yet another feature the Japanese would copy many years later, a crankcase that separated in the horizontal plane.
Apart from helping to eliminate the possibility of oil leaks, it also served a more useful purpose. It enabled the engine's car-type split big end bearings to be renewed without need for complete dismantling.
Details in the motorcycling press at that time failed to mention the engine was of Triumph's own design. It had, in fact, been originated by Bercley, the Belgian motorcycle manufacturer based in Brussels. Presumably Triumph would have built it under licence rather than buy it in. However, before negotiations could proceed much further the 1914-18 war intervened. Instead, Triumphs found themselves working flat out to manufacture their memorable model H 550cc single which would see active service in the hands of army despatch riders.
Concept of a vertical twin
It seems as though Triumph always had the concept of a vertical twin at the back of their mind, as towards the end of July 1933 they announced yet another design, their new model 6/1 twin. Val Page was the man behind this design, which incorporated many novel and ingenious features. A massive machine by today's standards, his 649cc twin had been designed mainly for sidecar use, as instanced by having a rear brake pedal that could be locked on to prevent the outfit running away if it was parked on a slope. Unlike the earlier Triumph twin, Page's design had pistons that rose and fell in unison, with a one-piece forged crankshaft and a single camshaft at the rear of the engine. Unusual was the fact that the primary drive comprised a pair of double helical gear pinions. This meant the engine ran clockwise, contrary to current practice. Built along semi-unit construction lines, the four-speed gearbox bolted to the rear of the engine. Overall, the 6/1 twin was an impressive-looking machine, even though it lacked any real pretence at styling and had a hand gearchange (foot gearchange was an extra). It sold for £75.15s solo, plus an additional £17 upwards depending on the type of sidecar fitted.
A specially-prepared 6/1 outfit was put through the 1933 International Six Days Trial by Sales Manager Harry Perrey, to win a Silver Medal. Later, the same outfit and driver covered 500 miles at Brooklands in less than 500 minutes, to win for Triumph the Maudes Trophy, awarded for the most meritorious performance of the year under A-CU observation. Yet even after all this, sales never really matched up to expectations. By the 1936 Motor Cycle Show the 6/1 twin was no longer listed. Edward Turner was now in charge at Triumph and his own 500cc vertical twin was already sufficiently well advanced to permit its launch less than a year later.
At the very end of July 1937 the first description of Edward Turner's revolutionary twin made headline news in the motorcycling press. Nothing quite like it had been seen before – a vertical twin that was almost as slim as its 500cc counterpart, weighed 4Ib less (yet cost only £5 more), and was remarkably good looking too! Having been responsible for the design of the Ariel Square Four several years earlier, the idea of this latest twin had occurred when he decided to experiment by isolating two of the Square Four's cylinders to see how they would run on their own. At that time working for Ariel under Val Page's guidance, both were so visibly impressed by the outcome, Page is alleged to have said to Turner that it made him wonder why they had bothered with the four!
Turner's original prototype and the 1938 production models differed in a number of respects from the models that were to follow in 1939. Initially, the crankcase had only six studs to retain the cylinder block, but in 1939 the castings were changed so that an eight stud fixing could be used.
This change proved necessary after the more powerful Tiger 100 model had been produced, which used the same crankcase and cylinder block. This change, along with others of a fairly minor nature, continued into the early post-war era, although by then the girder front fork had been superseded by Triumph's own telescopic fork.
Features that continued in the design, to become a Triumph 'hallmark', were the hexagon headed screwed caps that provided access for the adjustment of the tappets in the rocker boxes, and the chromium plated tubes at the front and rear of the cylinder block that contained the aluminium alloy pushrods. Like the cylinder block, the cylinder head was also a single cast iron casting. Internally, a three-piece built up crankshaft assembly comprised a central flywheel with integral balance weights, to which was spigoted a short shaft with a web, a crankpin and a circular flange, bolted to each side of the centre flywheel. Each connecting rod was a Hiduminium forging with a white metal lined big end. Bore and stroke was 63x8Omm, to give a cubic capacity of 498cc. Power output was alleged to be 29bhp at 6,000rpm. When it came on the market at the 1937 show, the speed twin retailed at £75.
It may seem surprising that Edward Turner's original prototype should have survived, especially as the old Triumph works in Priory Street, Coventry, were completely destroyed during one of the Luftwaffe's 'blitzes' on the city. An old photograph of the assembly track there, reproduced in Bert Hopwoods's book Whatever Happened to the British Motorcycle Industry?, clearly shows CWK 41 in the background, perched on its rear stand.
Clearly it could not have been in the Priory Street premises when the bombs began to fall, so where it went during the intervening years is unclear. It was only during a customer's chance conversation with a Bournemouth supplier of parts that its presence was disclosed. The proprietor's brother claimed to have the oldest Triumph twin on record, and it had the registration number CWK 41!
Fortunately, the person that acquired it was a keen Triumph enthusiast who, on seeing it, realised it was the real thing on account of several unmistakable features that differed from those on any of the production models. It changed hands and was painstaking restored to its original authentic specification, right down to its black and silver colour scheme.
The engine bears the number EXP 1, and amongst other items there is no provision for, or even signs of, where the familiar triangular Triumph identification plate was subsequently mounted on the polished aluminium timing cover of the production models.
Although the new Triumph twin was first catalogued as the model T, this designation did not stay in force for long. Indeed, by the time of the 1937 Motor Cycle Show, about eight weeks after its launch, the model name Speed Twin had already been substituted. Whether or not there was any prior right problem with Henry Ford's previous use of the original model name for his car is no longer known, but unquestionably Speed Twin was a far better name to more than adequately sum up the potential of this quite remarkable model.
Whilst the design of the Speed Twin can be attributed to Edward Turner, and also its overall appearance, credit in the latter respect must also be given to Jack Wickes, Turner's right-hand man. Wickes had joined Triumph as a young lad in 1931, and Turner soon became sufficiently aware of his potential to make him his personal assistant. Wickes showed a particular flair for styling, and thereafter Turner would always refer to him as 'my pencil'. Theirs was a working liaison that lasted for 43 years and it was Wickes who made the final arrangement drawings of the Speed Twin to visualise what the finished design would look like.
The Speed Twin's debut had a devastating effect on the motorcycle industry such that in no time at all the other major motorcycle manufacturers were striving to originate their own designs to rival the Triumph. Had it not been for World War 2, several other vertical twins would have been on the market very much earlier.
It is interesting to note that Edward Turner had designed his Speed Twin with the objective of a 90mph maximum speed in mind and that when it was first tested, this was the exact speed recorded. Many famous people endorsed the Speed Twin's capabilities, including Sir Malcolm Campbell, at that time the holder of the World's Land Speed Record. To use his own words "The Triumph Twin has no equal. It is a machine eminently suited for all purposes, is an extremely sound engineering job, and the workmanship is superb." As if to endorse this, a Speed Twin (in company with a Tiger 100) won the Maudes Trophy for Triumph in 1939, again at Brooklands like its predecessor.
At the same track on another occasion yet another record performance was achieved. Ivan Wicksteed, riding a supercharged Speed Twin, broke the track's 500cc lap record at 118.02mph, a record which still holds good today. No wonder the New Scotland Yard Police ordered a whole fleet of Speed Twins for the mobile units.
It is now history that the Speed Twin continued in more or less its original guise right up to, and including, 1958. Furthermore, it gave rise to a number of variants that included the 350cc 3T and the 500cc Tiger 100, the bigger capacity models such as the 650cc 6T Thunderbird, the high performance Tiger 110, and the immortal T120 Bonneville, and the competition model, the 500cc TR5 Trophy twin that brought Britain successes in the International Six Days Trial.
Unit construction engines eventually took over, but even then much of the original Triumph concept still lived on. Could Edward Turner ever have imagined that motorcycles bearing allegiance to his basic design of 1937 were still being made almost six decades later and that they would have had such a devoted following all over the world?
See also When was it that? contents