1970 Triumph Bonneville

1970 Triumph Bonneville Background & History

The 1970 Triumph Bonneville T120 was not only the high water mark in Triumph 650 development, and the year that most people favor as ‘the best Triumph Bonneville ever built’, it was also the last year before the dreaded Oil-in-Frame bikes arrived, and all the problems with cash-strapped owner BSA began to surface. At this point the Meriden factory was turning out 900 Triumph Bonnevilles a week.

The 1970 Triumph Bonneville really does represent the best of what Triumph twins had to offer at that point. But, relative to the changing market at that time, now rife with Honda 450 DOHCs and 750/Fours, Kawasaki triples and the like, the Bonnie was sorely lacking in some key areas: No 5-speed, no disk brake and no electric starter. And now that the public was becoming accustomed to the high level of quality and a “just put gas in it & go” maintenance regime that the Japanese bikes offered, the 1970 Triumph Bonneville started looking like an antiquated, unreliable, oil leaker that vibrated badly…and rightly so. All these things were true, but in 1965, no one cared, because all big-bore bikes were like that. Now that people had a choice, most of Triumph’s traditional buyer profile went with a Japanese bike, because they didn’t want to get stranded, and they didn’t want puddles of oil on their garage floors.

Stuck in The Old World

There is no more true indictment of the British motorcycle industry as a whole, back then. They were stuck in the past and failed to even see the future, let alone grasp it. Edward Turner, the father of the seminal Triumph Speed Twin and the Ariel Square Four, and Managing Director of Triumph and then BSA, spent 8 weeks in Japan in 1960 where he saw them producing 62,000 motorcycles per month, more than Triumph Motorcycles would ever produce, even on their best year. He was apparently unfazed by it, and changed nothing upon his return. Like the British motorcycle industry as a whole, Turner was so stuck in his old ways that he couldn’t see beyond making constant improvements to his same old designs. He had no interest in retooling to build modern engines, when his venerable vertical twins were cheap to build and fast enough to do the job, in 1960, at least. Turner came away with the conclusion that the Japanese were hopelessly backward and that the Brits were on the right track. Talk about hubris?!

In addition to archaic thinking, Triumph, which had been owned by BSA since 1951 was starting to be ‘messed with’ by its parent company. BSA bought Triumph from Ariel-owner Jack Sangster in 1951, but had the good sense to leave well enough alone, despite the fact that almost the entire BSA twin-cylinder product line was in direct competition with Triumph’s, and Triumph usually won. They were faster, prettier and sold better. But, during the 1950s, BSA was one of the largest and richest companies of any kind in the world, and by far the world’s largest producer of motorcycles, and had the legendary Gold Star, so no problem. But, Sangster got a seat on BSA’s board of directors as a condition of the Triumph purchase, and before long we was running the whole show. He sold off most of BSA’s prized assets and ran the company into the groud, likely enriching himself in the process. He retired in 1961 but the damage was done. By the late 1960s, BSA was on the ropes, having sold off all its best assets and being managed poorly. They turned to Triumph for salvation. They had plans to unitize the two vertical twin lines, the Triumph 650 and the BSA 650. But that would be next year…

1970 Triumph Bonneville is the Last Pre-Oiler

The 1971 model year would see lots of changes. A whole new frame, running gear and bodywork were introduced, everything was new except the one item that they should have changed: the engine. It was basically the same engine that Edward Turner designed in 1938, so it was anything but modern, by 1970 standards. Saddled with a power shortage when compared to the big Japanese bikes of the day, wicked engine vibration, reliability issues and relentless oil leaks, Triumph left the engine alone and changed everything else. This new frame held the oil in the 3-inch diameter backbone, eliminating the need for a separate oil tank, and hence the name “Oil-in-Frame”, and it became the defining element that set the 1970-or-earlier Triumph 650 apart from the 1971-and-later version.

1970 Triumph Bonneville Model Designations

The 1970 Triumph Bonneville really is probably the best one ever built, its certainly one of the prettiest. They run great, they’re fast, they handle fantastic and stop well. As classic British motorcycles go, this is just about as good as it gets. Model designations remain unchanged: T120R was the Road or street version with down pipes; and T120C was the off-road/trail/street scrambler (sort of an Enduro, or what they call today a dual sport) with high side pipes (they’re super-rare, so you don’t often see one).

The 1970 Triumph Bonneville received several significant engine upgrades.  Check out the cross-over pipe between the two header pipes.  1970 was the first year for that.

1970 Triumph Bonneville Engine

1970 Triumph Bonneville model year changes started with Engine #JD24849. Crankcase ventilation, always a problem with vertical twins where both pistons rise & fall together, was revised and the previous timed breather eliminated. Now the engine breathed through the primary chain case, via 3 holes drilled between them, then out a vent tube behind the clutch & out a rubber hose that ran all the way to the back of the bike, along the left edge of the rear fender. This system yielded a second benefit by keeping the primary always well oiled, but allowing any excess oil to run back into the engine through the holes.

Unified or UNF (American) threads continued to work their way through the engine and the 1970 Triumph Bonneville. Minor changes were made to cams, timing gears, tach drive and alternator cable. Plastic plugs were added to the Amal Concentric carbs to allow easy draining of the float bowls. The gearbox (transmission) was extensively modified for 1970. Changes to the inner cover, selector rod, mainshaft bearing circlip, aluminum-bronze shift forks with rollers (replacing steel forks), new cam plate and leaf spring were all aimed at better shifting. New oil-filled ignition coils (Lucas 17M 12) were smaller than the units they replaced.

The 1970 Triumph Bonneville was the last one with truly classic looks.

1970 Triumph Bonneville Frame & Running Gear

With a new frame coming for 1971, changes to the 1970 frame were minimal. A new front engine mount now had removable triangular mounting plates that bolted to the front frame rails and the nose of the engine, making it easier to put the engine in (for the Meridian factory) and to take out. Minor changes were made to the front forks, also soon to be obsolete. The rear brake anchor rod changed from tubing to flat steel. A chromed grab rail was welded on to the rear fender mounting loop and the seat was lowered slightly. The colors for 1970 were Astral Red (maroon) and Silver with Gold pinstriping. Fenders were again painted, this time in Astral Red with the center stripe being in Silver separated by the pinstriping.

In the end, those buyers in 1970 didn’t know how good they had it. The 1971’s would come late in the year and wouldn’t be very well received. The 1970 Triumph Bonneville 650 really is a gorgeous bike, and one of the finest, if not THE finest, Classic British Motorcycle in the world. (My opinion, of course. But, the Norton Commando was also a fine machine worthy of that title.)The Triumph Bonneville certainly would be on a very short list indeed, and as Bonnevilles go, 1970 was probably the best. It’s certainly one of the most sought-after today, by collectors and enthusiasts alike. They’re not only drop-dead gorgeous machines with loads of history, but they’re fast and they handle great, even by today’s standards.

1970 Triumph Bonneville Specifications

---

Triumph Bonneville Books

---

---

---

---

---

---

---

---

---

---

---

---

More Triumph Bonneville Pages

1959 T120 Bonneville

1960 T120 Bonneville

1961 T120 Bonneville

1962 T120 Bonneville

1963 T120 Bonneville

1964 T120 Bonneville

1965 T120 Bonneville

1966 T120 Bonneville

1967 T120 Bonneville

1968 T120 Bonneville

1969 T120 Bonneville

1970 T120 Bonneville

1971 T120 Bonneville

1972 T120 Bonneville

1973 T140 Bonneville

1974 T140 Bonneville

1975 T140 Bonneville

1976 T140 Bonneville

1977 T140 Bonneville

1977 T140J Silver Jubilee

1978 T140 Bonneville

1979 T140 Bonneville

1980 T140 Bonneville

1981 T140 Bonneville

1982 T140 Bonneville

1983 T140 Bonneville

1983 TSS Bonneville

1983 TSX Bonneville

Hope you're enjoying my website.  Glad you're here, take some time to look around.  I'm just getting started though, with lots of great content, pictures and specs on literally hundreds of classic British motorcycles left to go.  It is my goal to cover every year of every make, and every model of British bike.  You can join me in my quest.  If you have a classic Brit bike, take and/or send me some great photos of it along with a description.  Email coming soon.  More pages coming soon.  Please be patient, and hold on to your hat.  Thank you for visiting ClassicBritishMotorcycles.net.

Copyright 2024 by ClassicBritishMotorcycles.net.  All rights reserved.

---

---

Whitworth Tools for sale

---

---

2025 Classic Motorcycle Calendars are here!

---

---