Edward Turner's vertical twin, the Triumph 5T
After Valentine Page left Ariel in 1932, Jack Sangster promoted Edward Turner to chief designer and technical director of the re-structured company. Turner was the exact opposite of Page: He truly had his finger on the pulse of the motorcycle buying public and could predict — or perhaps create — market trends with unerring accuracy.
Late in 1935, after Page had seen the writing on the wall and moved on to a new post at BSA, Triumph, which then built cars and motorcycles, decided to cut their losses and concentrate on automobile production. Turner seized the moment and offered to run the business if Sangster would purchase Triumph’s motorcycle concerns.
In January of 1936, Turner took control of the renamed Triumph Engineering Co. Often working late into the night and on weekends, he produced a design for a vertical twin of his own. Totally different from the (now discontinued) 6/1, the new machine was shown to the press in mid-1937.
Displacing 498cc, Turner’s twin had a 360-degree crankshaft with a heavy central flywheel supported by large ball bearings. A pair of gear-driven camshafts operated the two valves per cylinder via short pushrods running through chromed tubes in the front and rear of the cylinder barrels. Ignition and lighting were by a Lucas Magdyno, which sat directly below the single 15/16-inch Amal Type 276 carburetor. The new twin produced 27 horsepower at 6,300rpm.
Primary drive was by chain to a foot shift, 4-speed Triumph gearbox. The frame and cycle parts were the same as the 500cc Tiger 90 single. Introduced to the press as the model “T” and later cataloged as the Triumph 5T, the machine resembled the single in profile and actually weighed 5 pounds less. The latest twin set new standards for easy starting, acceleration and smooth power, and was universally acclaimed by the magazine testers of the day. In its October 1937 road test, The Motor Cycle clocked a mean top speed of 93.75mph with a one-way maximum recorded at 107mph. “Truly an amazing performance for a fully equipped five hundred,” the magazine said. The Triumph 5T Speed Twin was exactly the right bike at the right time, and at the right price. It became an instant success and orders, including a large fleet order from the Metropolitan Police force, flooded in.
Although largely trouble-free in service, race track use would soon highlight design weaknesses. Brooklands racer and record-breaker Ivan Wicksteed found that, under prolonged full throttle, the cylinder barrels would shear off just above the crankcase joint. In his quest for lightness, Turner had failed to allow sufficient metal in that area. To his credit, Turner reacted swiftly. When the sports model of his twin, the Tiger 100, was announced for the 1939 season, the new design boasted eight rather than six studs to hold the barrels in place. This new arrangement was standardized on the 1939 Speed Twin.
The Triumph 5T was such a success it revolutionized the entire industry in a way that no machine had ever done before. Only one design since has had such a profound influence — Soichiro Honda’s 4-cylinder CB750. Had Page’s 6/1 twin seized the market instead, perhaps we’d be celebrating it, not Turner’s twin. MC
Read more from Simon Davis about Triumph's First Twin.