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The Very Best Bonnie

Triumph’s T120 Bonneville has stood the test of time as a  serious street bike, but the 1970 version was especially choice.

With the announcement of Triumph’s new 2016 1200cc Bonneville, it seems like a good time to look at the icon that lent its name to the new bike: the 650cc Triumph T120 Bonneville of 1959-72.

The Bonnie was, of course, named for the famed Utah salt flats where, 60 years ago, Johnny Allen set a new flying mile record of 214 mph in the “Devil’s Arrow,” a streamliner fitted with two Triumph 650cc Thunderbird engines running methanol fuel. Though the AMA recognized Allen’s record, the FIM refused to ratify it because their observers weren’t there. Triumph sued FIM—and made much of the ensuing publicity!

So when a dual carburetor version of Triumph’s top-of-the-line 650 Tiger 110 was announced for 1959, it bore the name “Bonneville,” and carried a decal stating  “World Speed Record Holder.”

The first Bonnie used Triumph’s pre-unit 649cc OHV parallel twin fitted with dual Amal 389 Monobloc carburetors. Into the engine went the performance E3134 intake cam and a raised compression ratio of 8.5:1, thanks to a new cylinder head with splayed intake ports. Otherwise, the Bonnie was similar to the T110, including the trademark headlight nacelle. Claimed output of the T120 was 46 horsepower at 6,700 rpm.

The extra performance highlighted some high-speed handling issues, which Triumph attempted to fix with a duplex downtube frame in 1961. But it wasn’t until the unit construction Bonnie of 1963 with a new single downtube frame that the Bonnie became a fast, stable and quick handling roadburner. 

In 1966 Triumph produced a TT version of the Bonnie minus lights and mufflers to suit US off-road racing. In 1968, the Bonnie got the BSA-Triumph group twin leading shoe front brake, which significantly improved stopping. This was also the last year of the optional “emasculator” parcel grid option with the UK-size five-gallon gas tank. And in 1970, there were revisions to the engine mounts to make removing and replacing the engine easier and the breathing system (to help stem oil leaks).

It was in 1969 that Malcolm Uphill on a T120R Bonneville Thruxton prepared by Doug Hele’s Meriden comp shop, completed the Isle of Man Production TT at the remarkable average speed of 99.99 mph, winning the event. This achievement inspired Dunlop to name their new street tire the TT100.

1971 brought the oil-in-frame debacle. The concept was sound: install the T120R engine in a new welded steel tube frame (dispensing with Triumph’s time honoured bolted-up, lug and braze item), which would also carry engine oil in the top tube. The problem: in order to accommodate both the BSA and Triumph engines in the frame, the seat height became too tall for all but the leggiest riders. 

BSA-Triumph’s precipitous decline around this time is well documented. Suffice to say that the Bonnie acquired a five-speed gearbox in 1972, 750cc and a front disc brake around 1973, and continued in production until 1984 at the Meriden plant under the control of a workers’ cooperative. Then a young, maverick property developer called John Bloor bought the Meriden site, along with Triumph’s intellectual property….

The 1970 Triumph Bonneville shown here has a checkered history. Sold originally in Alberta, it succumbed to a blow-up, whereupon the engine was removed from the frame. Through a messy divorce, the chassis and wheels went one way and the engine the other.

Langley, BC’s Geoff May, at the time living in Wild Rose Country, bought the rolling chassis as a project and then went looking for a suitable engine. Enter John Oland of Edmonton’s Motoparts store. Oland had a 1970 engine he was prepared to sell to May—which the matching numbers soon revealed to be the engine fitted in the first place!

Relocating to BC, May reassembled the engine and reunited it with the chassis. Since then, Rick Brown of Spence’s Bridge, BC has repainted the gas tank and side panels. The only deviations from stock are the Boyer-Bransden ignition and a Harley-Davidson dual output ignition coil. And before you point out the unpainted fenders, Canadian market Bonnies used stainless steel instead.

Riding the T120 now, it’s sometimes hard to envisage what a potent package this was in its day. With a top speed of over 110 mph, the Bonneville was pretty much the fastest bike in production in 1959. Now it feels compact—small, even—with a low seat and short reach to the bars. It could be mistaken for a 250, except for the serious off-idle grunt. Vibration is tolerable (much less than a contemporary 650 BSA), and 70 mph cruising is comfortable with the optional 20-tooth countershaft sprocket. Brakes are much better than you’d expect and handling is confidently nimble. I’ve yet to ride the new 1200, but if it’s as much fun as the original, it should be a bestseller.

by Robert Smith Canadian Biker Issue #318


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