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1971 Triumph TR6

1971 Triumph TR6

The 1971 Triumph TR6 saw the introduction of the new oil-bearing frame & all new cycle gear. This photo is of a ’71 TR6 Tiger. The TR6 had a single carburetor while the Bonneville had two.

ABOVE: Everything was all-new on the ’71 TR6 and Bonneville, except the engine. The new oil-bearing frame was all-welded, which yielded a much lighter frame than the pre-’71 brazed-lug frames.

All TR6’s were known as “Triumph Tiger”. There were 4 basic models: TR6R (Roadster & now the standard version), TR6C (with high pipes), TR6P (Police), & TR6RV (a Roadster with an optional 5-speed transmission). Engine & Frame Numbers ran from PE003157 to HE029817, built from November 11, 1970 to August 7, 1971.

The 1971 Triumph TR6 & it’s sister bike, the 1971 T120 Bonneville were complete revamped from stem to stern, with a complete redesign that included a new oil-bearing frame, new forks, new wheels with conical hubs, new cycle gear & bodywork & a whole new look. The engines were about the only components that didn’t get substantial change (other than the option of a 5-speed gearbox for the first time). On the surface, this sounds like a really good thing to do for Triumph Motorcycles, especially considering the withering competition beginning to pour in from Japan. Unfortunately, quite the opposite proved to be the case.

ABOVE: The well-developed unit-construction 650 remained more or less unchanged. However, due to poor design, it wouldn’t fit in the new frame in one piece. The rocker boxes had to be removed before the engine would slide into place, then were reinstalled. This was cleverly remedied in 1973 with the new 750, whose barrels were one fin shorter than the 650.

After years of market & racetrack success, Triumph was on a roll, at the end of the 1960s. But times were a’changin’, as they say. DOHC 450 Hondas & of course the mighty Honda 750 Four changed the game. Triumph twins were no longer the weapon of choice for high-performance riders. They were beginning to show their obsolescence. The Japanese motorcycle makers, Honda in particular, were advancing the art & science of motorcycles, motorcycle design & manufacture, looking for new & better ways to do things. The British motorcycle industry, at the time, were trying to find ways to reuse their old, antiquated designs & tooling, they didn’t want to invest in new designs or manufacturing techniques. Some of the tooling used to build the 1971 Triumph TR6 were more than 3 decades old, by this time! Some machines were worn so badly that blocks of wood had to be used to take up the play!!

ABOVE: The new 1971 Triumph TR6 was actually a very handsome machine, and looked much more modern than the earlier machines.

Unknown to most people at the time, Triumph Motorcycleswas solely owned by BSA. You see, back in the 1930s, Triumph was in financial trouble & so was bought for a song by Ariel Motorcycles owner, Jack Sangster. He is the one who brought in Edward Turner to design the seminal 1938 Triumph Speed Twin, the bike that set the pattern for every British vertical twin for the next 45 years. Sangster was more of a wheeler-dealer than a motorcycle enthusiast. He just saw the business as a way to make money. Pursuant to this, he sold Triumph to BSA in 1951 & retained a seat on the BSA Board of Directors. At the time, BSA was one of the largest multinational corporations in the world, making everything from armaments & steel to buses & heavy equipment & they were flush with success. By the early 1960s however, Sangster had presided over the selling off, at bargain prices, most of the company’s assets, until by the mid-60s, what was left of BSA was weak & out of money. Triumph’s success was just about the only bright spot for BSA, yet BSA hated Triumph as a rival. Management was horrible, bad decisions to even worse & they rode their once-successful empire into the ground!

After years of underinvestment & bad management, BSA got a big ideas: Rather than spend our dwindling resources on new motorcycles, lets build a lavish ‘technology center’ at this cool old mansion in the country (called Umberslade Hall), then bring in lots of high-priced talent that has no motorcycle experience. Aerospace engineers redesigned the entire Triumph 650 line with new oil-bearing frames, forks, wheels, the works. But delays in getting the Meriden factory the final blueprints pushed the production start date all the way out to November 1970 (it would normally have been in August). When the factory built the first frame & tried to put an engine in it, they found that it would not fit. Once in place, it fit fine, it just couldn’t be shoe-horned in, on the assembly line.

The engineers at the Meriden had to quickly create a solution, as the design of the frame was fixed & couldn’t be changed. They hastily designed a new cylinder head, rocker boxes & 2-piece head bolts, all as a means of creating the needed clearance to install the engine.

The new rocker boxes now had screwed-in access plugs in either side, which allowed better access for a feeler gauge during valve adjustment. New pushrod tubes now featured an unbroken top rib with holes drilled through it, rather than the former castellated design, aimed at curing oil leaks. Staring with #GE27029, a new metric timing-side mainbearing was installed, requiring a new crankcase half & modified crankshaft dimensions.

Starting with #GE027729, a long-awaited 5-speed gearbox became optional on all 650 twin models, including the 1971 Triumph TR6, which with 5-speed was known as a TR6V. The same old 4-speed gearbox was still standard equipment across the model line.

Despite all the teething problems, the new Umberslade Hall oil-bearing frame for the 1971 Triumph TR6 & the 1971 Triumph Bonneville was actually a pretty good frame. For the first time in Triumph Motorcycle history, it was an all-welded, one-piece frame. The new twin-downtube frame had a large 2-1/2″ diameter backbone & seat post that ran from the steering head to the bottom of the frame & it was filled with oil. It was all supposed to be filled with oil, about 6 pints, more capacity than the old oil tank it replaced. However, the “brain trust” at Umberslade Hall decided, at the last minute, to place the oil filler under the nose of the seat, instead of just aft of the steering head. One possible reason was said to be ‘oil frothing’. Either way, it cut oil capacity to just 4 pints, now 1 pint short of the old oil tank. It had a much stronger swingarm pivot, with a new forked swingarm. The steering head now had tapered roller bearings.

Rear suspension units (shock absorbers) were 12.9″ Girlings with exposed chromed 110lb springs. The forks were all new & very modern & attractive. It had hard-chromed stanchions & alloy sliders with 4 studs at the bottom of each one, retaining each end of the axle. Gone were the gaiters, now it had neat little rubber sliders. Looked great, but the exposed fork legs allowed dirt in & wore the seals prematurely. The sliders had no bushings, so the rode directly on the stanchions & this too wore prematurely, a condition that could only be cured with all new sliders.

1971 Triumph TR6C TROPHY

In days of old, the “C” on the end of a Triumph‘s model-name nomenclature always denoted the “Competition” model, or accurately the “Off-Road Model”. Back in the 60s and 70s, they called bikes like this “Scramblers”, generally characterized by their high exhaust pipes, snaking along the left side of the bike. Originally conceived to give more ground clearance in TT and “Scrambles” races, where they were always turning left, they moved the exhaust out from the bottom of the engine on either side, and pushed them up as high as practically possible. Many a leg have been burned on such pipes, even despite the heavy heat-shielding. Back in the day, there were real differences between the TR6Cs and the street-going TR6Rs. But by 1971, those differences had largely vanished, mostly in an effort to cut costs. Now the only real difference was the exhaust pipes and the name badges.


Model Designations:





Engine type


Bore & Stroke




Engine output

Primary drive

Primary sprockets


Gearbox, standard

Ratios, overall:

1st, bottom



4th, top

Gearbox, optional

Ratios, overall:

1st, bottom




5th, top

Final drive

Final sprockets

Frame type

Suspension, front

Suspension, rear

Brake, front

Brake, rear

Tire, front

Tire, rear

Fuel capacity


Seat height

Ground clearance



Street Scrambler/Off-road/Competition



Air-cooled OHV vertical twin

649cc / 40.0 ci

71mm X 82mm / 2.79″ X 3.23″


1- Amal Concentric R930/60, 30mm

12V battery & coil, Lucas

47 bhp @ 6700 rpm

3/8″ triplex chain X 84 links

Engine 29T X Clutch 58T

Multi-plate, wet

4-speed constant-mesh, right-foot shift






5-speed constant-mesh, right-foot shift







5/8″ X .400″ X 3/8″ chain X 106 links

Gearbox 19T X Rear 46T

All-welded, large backbone, oil-bearing

Telescopic fork, 2-way hydraulic damping

Swing arm, 2 Girling dampers

8″ TLS drum in conical hub

7″ SLS drum in conical hub

3.25″ X 19″ Dunlop

4.00″ X 18″ Dunlop

3 Imp gal (US) / 4 Imp gal (UK & export)

56″ / 142 cm

34.5″ / 87.3 cm

7″ / 18 cm

383 lbs / 173.9 kg