History of the T140

 History and development

Triumph’s original 650cc T120 Bonneville, itself derived from the 500cc Speed Twin,  was replaced in 1973 by the T140 Bonneville, the same basic machine but with a 750cc engine. This increase in engine size was driven largely by demand from the U.S.A. for larger, more powerful engines – a market which was being increasingly addressed by Japanese manufacturers..

Oil in Frame

The T140 models were all equipped with a 5-speed gearbox, and were launched with a front disc brake and drum rear and inherited the oil-in-frame design of the later T120 which had proved contraversial both then and now.

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 750cc engine was near identical to the 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 T140s 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.

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. Refined from the later ‘oil in frame’ version of the T120, the first few T140s, designated T140V, featured a larger-capacity engine of 724 cc, a five-speed gearbox option and indicators, but still retaining drum brakes and kick-start. Shortly after, the engine was further bored out to 744 cc and front disc brakes were fitted using single discs until 1982. In 1975, along with engine modifications, the gearchange lever was moved from right to left to comply with new regulations mandated for the American market and a rear disc brake fitted. Several T140 models followed featuring various modifications and refinements including electric starting from 1980 until production ceased with the closure of the Meriden works in 1983.

Although this should have been the end of the Bonneville, as it turned out it was not. Triumph Motorcycles was acquired by businessman John Bloor, who licensed a company called Racing Spares in Devon, run by Les Harris to manufacture the T140 Bonneville. These continuation bikes are known as the ‘Devon Bonnevilles’, which did not reach the market until 1985, and were not sold in the U.S. Production ended in 1988.