Triumph T140W TSS

Visually, the most unique aspect of the TSS is its Westlake 8-valve head and accompanying alloy cylinder barrels. They were smaller and somehow more shapeless than the traditional Bonneville top end. But the machine overall was still quite handsome. The wheels were “mag”-style alloy wheels by American Morris, shod in Avon Roadrunner tires, with dual Lockheed disk brakes up front and one in the rear. Bright stainless steel fenders contrasted the nice-shaped Italian-made 4-gallon gas tank which was painted black with big red spears. The rear air-oil shocks were also Italian, made by Marzocchi, using a strengthened swing arm. The Meriden Co-op was sourcing their OEM parts from all over Europe now, basically from anyone who would sell them to them on credit. The gauges (clocks) were made by Veglia of France. The fuel petcocks were from Pailoi in Italy. Germany suppled the Bumm mirrors, Magura choke lever and ULO turn signals.
By the 1970s, the Triumph Bonneville, and just about every other British bike still in the game, was looking more and more obsolete in the face of the Japanese onslaught. The Bonneville, once one of the fastest machines on the planet was hopelessly outclassed by big 4-cylinders from Honda, and screaming 2-stroke triples from Kawasaki. Even Triumph’s own triple, the Trident was too little, too late. What was really needed was a major infusion of capital to design completely new, totally-modern engines (like the Japanese), and state-of-the-art manufacturing and tooling to build them with the precision and on the scale of the competition. Of course, this never happened. The Brits were hopelessly short on cash and there was no one to step in and help. The British government at the time was very socialist and didn’t like “big business”, even though Triumph could hardly ever have been called “big”. By 1975, Triumph’s factory workers had taken over the plant and formed the Meriden Co-op, which was financially shaky from the start and only got worse until their final demise in 1983. However, what the scrappy Brits were able to accomplish, with so little to work with, is a testament to them and to the human spirit.
By the late 70s, the Co-op was producing only Bonnevilles, and precious few of those. Forever innovating on a shoestring budget, they became adept at creating limited runs of “Special Edition”-bikes, like the ’79 T140D Bonneville Special and later the Royal Wedding Commemoratives. But even this wasn’t nearly enough to turn the tides. Amid all this, Triumph’s plucky engineers, led by Brian Jones (no, not the Rolling Stone) secured the rights to Harry Westlake’s 8-valve head, which had been proven in racing and was used on Rickman’s cafe and road racers that used Triumph twin engines. They may not be able to build an entirely new engine of modern design, but they could apply their extensive racing acumen, and the new Westlake head, to the problem.

Triumph T140W TSS ENGINE

Westlake, a cylinder head designer with extensive racing experience with Jaguar and the like, put together an 8-valve top end and a new crankshaft for the Bonneville engine. Of course, 4-valves-per-cylinder are quite common today, but in 1982, it was considered exotic racing tech. Each of the 4 valves were smaller than their 2-valve counterparts, with two for intake and two for exhaust in each cylinder, set at a much steeper angle than before. The 2-valve Bonnie has a true hemispherical combustion chamber with its valves set at a 90-degree included angle. The new Westlake head set them at 30-degrees. The pistons were deeply notched to clear the valves, so taller domes allowed a 10.0:1 compression ratio. The alloy cylinder block had steel liners.
The new crankshaft was a one-piece forging with larger-diameter big-end rod bearings. It was much stiffer and also better balanced than the standard Bonnie cranks, and helped the TSS to deliver fairly smooth power. Interestingly, the cylinder bores were set farther apart than in the standard Bonneville engine to allow more cooling air to pass between them. The required that the connecting rods be offset slightly. This arrange was supposedly good for 10,000 rpm, compared with 7,500 for the stock crank. UK-spec TSS’s got two 34mm Amal MkII carburetors, while US-spec bikes used Bing constant-velocity carbs instead. All TSS’s also used Triumph’s new, but rather anemic electric starter system that was chain-driven off the intake cam, resulting in the rather lumpy looking timing cover.
In the end, the TSS like everything else Triumph tried, was too little too late. In all, it was a nice bike, fairly fast with almost 60 horsepower, and yet smoother than any Bonneville to come before it. It handled well, and it was a very good looking bike. But it was expensive when compared to faster, more sophisticated bikes from Japan, and the Meriden Co-op simply didn’t have the financial resources or the marketing muscle to produce many bikes. All told, only 438 TSS’s were ever built. In the end, it didn’t do anything to prevent the Co-op’s voluntary liquidation and closure. The TSS was built for two model years, 1982 and 1983, and the legendary Meriden factory where so many great Triumphs were built closed its doors for the last time on August 26, 1983. While never actually called a “Bonneville”, clearly Bonnies were the Co-ops only product, the mechanical lineage is undeniable, and the T140W model designation was in keeping with Bonneville nomenclature.


Model Designation
Years produced
Production numbers
Horsepower @ RPM
Bore & Stroke
Compression ratio
Fuel system
Primary drive
Final drive
Brakes, front
Brakes, rear
Suspension, front
Suspension, rear
Tire, front
Tire, rear
Seat height
Dry weight
Fuel capacity
Fuel consumption
Top speed
1982 & 1983
1982: 226; 1982: 112
744cc / 45ci
58hp @ 6,200rpm
76mm X 82mm
2-Amal 34mm MkII (UK) / 2-Bing CV (US)
Triplex chain
Multi-plate, wet
5-speed constant mesh, left-foot shift
2-Lockheed hydraulic disk w/254mm rotors
1-Lockheed hydraulic disk w/254mm rotor
Telescopic forks, hydraulic
Marzocchi shocks w/strengthened swing arm
54.5 in / 140.3mm
32.5 in / 77.5mm
403 lbs / 182.8 kg
4.8 US gal / 18.2L
52.7 MPG observed
124.14 mph / 198 km/h

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Last updated 12/7/17

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