Triumph TR5
The parallel twin that captured the imagination of the British bike buying masses
Take a look at the kind of motorcycles that British manufacturers were turning out in the mid-1930s and you can see why Triumph’s 500cc twin was such a revolutionary design.
Most 350 and 500cc British motorcycles of the era were singles, mass market machines fitted with side valve or OHV engines, and anything bigger was likely to be a V-twin. While there were other more exotic concepts such as Ariel’s first Square Four and the Matchless V4, the single held sway. But for now, the single had reached the limits of its development, and squeezing any extra power from the long-stroke engines being produced just led to more vibration and unreliability.
Triumph had already developed a twin, Val Page’s 6/1 650. This was a handsome machine, but it failed to capture the public imagination.
In 1937 Edward Turner’s Speed Twin 5T, the replacement for the 6/1, was launched and suddenly motorcycles got modern.
The 5T model’s cycle parts were largely the same as those used on Triumph’s range of singles, but things were restyled, and it was the engine that made all the difference. Turner’s new twin engine was lighter than its fellow singles, was as narrow at the crankcase, and was essentially a twincylinder single, with both pistons rising and falling together.
The new 500 twin had cast iron cylinder block and head with removable alloy rocker boxes and a four-speed gearbox.
The two camshafts were in the simplest and most accessible locations fore and aft of the cylinders, and the lines of the engine were much less cluttered than those of their rivals. There was a vertically split crankcase of a concept that would stay in production until the late 1980s, with a built-up crankshaft. The use of a 360-degree crank meant that the same Magdyno fitted to the singles could be used.
The arrival of the T series forced rivals to come up with their own twins, and soon the compact and fast parallel twin became the wave of the future.
Sporty, stylish and smart, the 5T sold well for two years until the outbreak of war, when production ceased as Triumph moved to wartime production making tens of thousands of their OHV and side valve singles for the War Office.
The bombing of the Triumph factory in Coventry saw production moved at first to a temporary factory in Warwick, before the establishment of a new plant at Meriden.
Triumph put the 5T engine to work in the war effort, and as the engine was lighter, smoother and shorter than their singles, they adapted it to become a generator powerplant which was used to charge the batteries that powered increasingly sophisticated radar equipment in Lancaster bombers and as an air portable unit that could be parachuted to troops on the front line. To keep the weight low, the 5T engine was fitted with a silicon alloy cylinder and head. The close finned alloy barrel kept cool with a fan.
In the postwar era, Triumph quickly turned from military to civilian production, and while rivals were repainting old WD models to fill the showrooms, Triumph relaunched their twin in two versions, the Speed Twin and the sportier Tiger 100. These were largely unchanged from 1939, apart from the use of two-way damped telescopic forks, which as well as being more modern than the girders, reduced unsprung weight enormously, as well as offering six inches of travel.
This desire to reduce unsprung weight moved to the back wheel with the introduction of the Triumph sprung hub, which provided a kind of rear suspension. The sprung hub was light, cheap, and would fit in the existing rigid frame. It was also complicated and prone to the mechanism dramatically exploding as the under-pressure springs would release themselves, should an inexperienced mechanic attempt to dismantle it. Triumph had a warning for the unwary cast into the hub.
WHAT IS IT? GOOD POINTS?
One of Triumph’s best twins, capable on road and a winner off it
BAD POINTS?
Some model-specific spares are going to be hard to come by. Be aware of this if buying a project
COST?
A project £4-5,000. Good runner £8,500-£12,000. Concours/museum quality £15,000-£50,000 (with competition heritage)