Triumph Bonneville T140

IF YOU'RE LOOKING for an all-weather, all-purpose, everyday classic British bike, you’re probably staring straight at a 750cc T140 Triumph Bonneville. A lot of negative criticism has been hurled at these machines, notably citing problems with vibration and oil leaks. But the fact remains that these machines offer excellent handling, good braking, decent enough suspension, an acceptable turn of speed, and have better parts back up than just about any other classic British bike in the market place.

 As for the vibes, these never were as bad as some suggested (although a poorly set up Bonnie with an unbalanced crank is a minor torture). And the much-mentioned oil leaks are no worse than those of other British bikes. But because these work horses are used more, so the leaks are seen more often. Almost nobody trailers one of these from show to show.

Not yet, anyway.

▲ Two of Sump's girls striking a pose on one of our T140s. It's the same everyday hack as seen on our humble YouTube video (see elsewhere on this page). We'd love to stop and tell you more about it, but the girls are calling. Know what we mean?

History and development

Launched in 1973, the T140 picked up where the 650cc T120 Bonneville left off, and the extra 100cc came with a penalty. Edward Turner, designer of the 1937 Triumph Speed Twin (the grandfather of all successive Meriden twins—and the inspiration behind a lot of other twins from rival marques) has been quoted as saying that he never intended his 500cc engine to be enlarged. Certainly to no more than 650cc.

But by the late 1960s, the Americans (in particular) were clamouring for more horses for their track and desert courses, and if the Meriden factory couldn’t provide the required upgrade, then the Yanks would.

And did.

Eventually, feeling the pressure of Japanese superbikes eating up showroom floor space and sales, and hoping to turn US aftermarket 750cc top-end kits into much needed dollars, the company acquiesced and finally built the long-time-coming 750cc twins.

Oil-in-frame chassis

These new machines were always 5-speed, and were launched with a front disc brake and drum rear and inherited the controversial oil-in-frame chassis trailblazed by the 650cc T120. That frame started out wrong, but ended up right, and has lasted around forty years without significant issues.

Styling was a pretty much orthodox British sit-up-and-beg configuration with a build quality that the Japanese bike industry still hadn't matched. Frames were hand welded. Tanks were hand striped. The overall feel was of a value-for-money, traditional machine, albeit manufactured around a design that could have been justifiably pensioned off in the mid 1960s.

The (nominally) 750cc engine was near identical to the (649cc) 650cc power unit. But the first machines off the line were (for production reasons) actually 724cc. Within months however, this became 744cc—which remained the cubic capacity of these air-cooled parallel twins until the bitter end.

 Development of the new seven-fifties was, by 1974, slowed by the now infamous industrial unrest at the Meriden factory in Warwickshire that saw production halted for around eighteen months—and, woe of woes, at a time when the Japanese were becoming increasingly aggressive and competitive; a fatal commercial combination that put a large number of nails in the coffin of what was left of the British motorcycle industry. Which, with Norton just about the hit the skids, was really just Triumph.

Rear disc brake and revised cylinder head

By the time the Meriden industrial situation/debacle was resolved, the Triumph Trident (which was in fact the true competition for its twin cylinder stablemate) was almost dead on its feet, leaving the "ageing" Bonnie desperately trying to claw back prestige and customers with a package that was beginning to show a lot of mechanical wrinkles.

 The Meriden engineers, however, were not giving up without a scrap, and the 750cc Bonnie and Tiger was, if not exactly technically brought up to date, then at least patched up enough to scrape it through the increasingly stringent noise and environmental pollution laws that were almost as big a problem as the incoming Japanese—and, come to that, the incoming Germans who, with their new range of BMW Boxer twins, were rapidly shedding their “old man” image and looking increasingly attractive to a younger aspirational biking set.

 And then there was Harley Davidson knocking on the door and slowly getting its act together with a range of brutally attractive, if expensive, 1000cc and 1200cc twins.

In 1976, a rear disc brake arrived. In 1978, the bike developed a new, parallel-port cylinder head (to replace the earlier splayed-head that had been a feature since 1959), while the TR7 Tiger, which had started with a single carb, retained it throughout).

That same year, new carburettors were introduced for the T140 (Amal Mk2s as opposed to Mk1s; the Tiger kept its Mk1), and overall, the bikes were looking more angular and modern—and a little too angular and modern for many marque diehards. Worse still, performance was down and vibration was up. At least, the modern generation of wannabe gonzo motorcycling journalists felt so, and said as much.

Loudly, and often.

Meriden under pressure

Unquestionably, such hostile press opinion cost the firm some sales—but perhaps not as many as you might expect. The average rider of the late 1970s wasn’t, after all, going to be fobbed off with an old tech, leaky, pushrod British twin when, for significantly less money, he could buy an up-to-the-second Japanese multi that could thrash the Meriden bike on any quarter mile length of straight.

However, on the curves it was a little different. In fact it was a lot different. At that time, Japanese bikes had notoriously bad handling, and British twins (and triples) were famed for their sure-footedness. The average Jap superbike had a huge hinge in the middle and (often) a distinct wobble when it approached anything like its theoretical top speed.

But the Japs were learning fast, and there wasn’t really any place else to go for the Bonnie; certainly not without radical revisions, for which there simply wasn’t the development cash anymore.

In 1979 the Yamaha 650 Special (twin) appeared; a devilishly handsome piece of kit that did pretty much all that the Meriden offering could do (except handle), and at a lower price. It was largely also oil tight, and vibrated less, and had a good electric starter. These 650cc Yams, since 1968, had built a reputation as dependable all-round machines, and they sold in huge numbers around the world.

But this particular Yam, with its cast wheels and black and gold livery, hit the right note during the right summer and had exactly the street cred required by contemporary riders looking to build or maintain a sub-hooligan wish-I could-afford-a Harley image. Whilst at the same time, the Yam Special was not so left-field that ordinary guys looking for a simple, decent, attractive everyday twin would shy away from.

▲ One of Sump's own T140s, lightly customised with Lester cast wheels, TSS side panels, a two-into-one-exhaust, a Bates headlight, wider handlebars, and bright yellow livery. The engine timing has been altered too for more overlap and better breathing. And that front wheel is an 18-incher (same as the rear), hence the non-ideal mudguard fit. We love it.

Bonnie Special and electric starters

Regardless, Meriden felt the pinch and rapidly responded with the T140D Special (Lester cast wheels, black and gold livery, two-into-one exhaust); a machine that in terms of looks and quality of materials easily shunted aside the Yam Special. But the king of the twins was on shaky ground (not least because it was 10-15% more expensive), and knew it.

The following year, an electric start appeared; the first on a British motorcycle that actually worked well. For a while, anyway. There were later problems with this hurriedly engineered system, but none of which can be shown to have really hit sales (except in the second hand market). And within three years of that auspicious event, having seen relatively minor (and some not so minor) revisions, the "legendary" twin was dead.

That was 1983.

Part of the problem was a collapsed US market. Part of it was business export market guarantee intrigues. Part of it was that the Bonnie was simply looking less and less relevant. And sales had truly plummeted during those last few years despite most riders bearing a grudging respect for the T140 (some of whom who were, naturally, always meaning to buy one, or at least cadge a ride on one someday). And of course the biking press, now that the dirty deed was done, said that it was a pity that the British bike industry was over. But never mind, we’ve still got the Japs ....

 It might have been kinder had someone pulled the plug a little earlier, because at the end of production, the 1973 flood of Bonnies had turned into a pathetic trickle pouring down the drain of history with bikes being offered in any specification and any colour, just so long as you bought something.

Please.

▲ 750cc TR7T Tiger Trail. Built between 1981 and 1982, these rare twins have a small but loyal following. Check our TR7T Tiger review.

Harris Bonnies and the end of the line

It was a sad end for a company that really loved its product; an end that enjoyed a short-lived resurgence in 1985 when the late Les Harris bought a short-term manufacturing licence and built another 1200 or so bikes up until 1988.

Today, these machines are as good as they ever were (whatever that means to you), with overall reliability much higher (thanks largely to retro-fitted electronic ignitions; first fitted as standard in 1979).

They’ll leak a little oil, which can be ignored without issue, or (mostly) fixed if you just take the trouble to rebuild them properly. On the plus side, a little black gold splashed around a motorcycle isn’t such as bad thing if you want to keep the lethal oxides at bay.

Overall, Bonnies and TR7s are nimble, tractable, decent stoppers, and maintenance light. And when they do go wrong, they can be sorted fairly easily. Also, they return around 50-55mpg. You won’t see much change out of 100mph, but acceleration is still pretty good, even two-up.

The seat height is fairly low at around 31-inches, and only those with extra short inside leg measurements will have to worry about getting both feet flat at the same time on opposite sides of the saddle.

Is this the right bike for you?

Most owners/riders wear open-faced crash helmets. But if you really must wear a full-faced lid, this is one of the few British bikes that will indulge your obsession with your bridgework without looking too ... well, naff. So much so that Meriden was keen to use full-faced helmets in its later adverts as if to prove to the world that what was pretty long in the tooth was actually very modern and cutting edge.

But which bike should you buy? The short answer is whichever one you most enjoy looking at—provided the price is in line with current market expectations. None of twins have particular "issues", except perhaps the electric start models (which need a little extra care with the starter gear sprag clutch), and the T140W TSS derivation (with its eight-valve head and other under-developed revisions). If you're considering an early bike (pre-1976), you're strongly advised to think in terms of left or right side gear change. It can make a major difference to some riders.

If you want to cut your maintenance chores a little further, and without a significant power penalty, buy a Tiger.

After a long time in the low value, low status doldrums, oil-in-frame Bonnies and Tigers have risen in value and prestige. And rightly so. For commuting, these bikes can easily take the daily rough and tumble, being nimble in traffic with enough presence to command some respect on the road. For touring, they're long legged enough to carry you for hundreds of miles a day, two up and with luggage, without blowing their cool and leaving you exhausted. And for Sunday fun and games on your favourite back roads, a 750—or 650—twin will do everything demanded of it by the average classic biker, with plenty in reserve.

They can be tuned and beefed up to show a genuine 115-120mph on the clock. But you'll also have to drop the bars and shift the footrests back to do it. The compression will need to be raised; bigger carbs will need to be fitted; and expect to do a lot of headwork (porting, polishing, and perhaps lighter valve springs).

Meanwhile, stripping some of the excess tin ware can cut the flab by around 60lbs, or more, thereby effectively liberating a few extra bhp at the bottom end.

If you like the T140 looks, but want something newer (and with the Triumph badge on the tank), the Hinckley Triumph T100 Bonnevilles are good value and they get better year by year. So okay, they haven't quite got the T140 style, but they're close (if you squint).

Alternately, check out something like the Thunderbird 900 or Thunderbird Sport. Both are triples, and both are excellent classic cruisers.

 Lastly, if anyone tells you that the oil-in-frame T140s are rubbish, just fix up a time and a place and let us know. We’ll send some of the boys round to sort it out.

Ownership tips

1. Use a quality 20W50 low detergent multigrade oil and change every 1500 miles maximum, or less. Change it every year, anyway.

2. Chrome discs make for worse braking. De-chrome, or replace. Un-chromed cast iron discs are superior.

3. Check the wiring looms carefully when buying. Many looms haven't been replaced in over 30 years. Worn looms are a fire risk.

4. Use the best fuel you can get, and avoid cheap supermarket petrol.

5. Rejuvenate the braking system by replacing old hoses. And change the hydraulic fluid at least every two years, or less. DOT 4 will do nicely.

6. Rough fork action can often be fixed by loosening the forks from the spindle upward (including yokes), and retightening in the correct sequence according to the factory workshop manual. Worn head bearings will advise you of the fact with regular clicks and clonks over road bumps.

7. Check regularly that the oil is returning. Raise the seat, unscrew the oil filler cap, and run the engine. There's a small pipe just visible at the top
of the frame elbow. Oil should squirt from that pipe in "glugs". You won't see a continuous stream. Get to know the feel of new and old oil.

8. Check the centre stand for smooth action and looseness, and check the side stand for sloppiness. T140s should elevate easily without giving you a hernia. If they're hard to raise, something is wrong; possibly worn bolt holes, or poorly manufactured stands (especially from the Far East).

9. Gears should change cleanly and click into place. You might occasionally get a first gear clonk. But beyond that, the gear changes should be fairly slick. They should slip into neutral when stationary. But naturally, they prefer to find neutral on the move at walking speed.

10. Clutches are fairly heavy, but should bite smoothly and progressively.

Keep a spare cable with you—or, at least, an emergency cable repair kit. All our T140s have been cable hungry.

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