Some builders find the exciting part of a restoration is the hunt for parts.
There’s no mistaking a Triumph Bonneville. Launched in 1959, the Bonneville was named to commemorate a 214.47 mph world land speed record set by Johnny Allen in a Triumph-powered streamliner at the Bonneville Salt Flats.
The looks, the sound and the power are all unique to the revered Bonneville model that, with the exception of a few years, has been in production for almost six decades.
Calgary’s Bob Klassen isn’t immune to the charms of the earlier models, and for close to three decades owned a unit-construction 1970 Triumph Bonneville.
During that time, he’s also built, and had a hand in building, close to a dozen pre-unit Triumph motorcycles.
A Brief History Lesson
That’s exactly how this 1962 Triumph Bonneville T120R came together. Before we get to the build story, we need to learn a little more about Klassen and his penchant for pre-unit Triumphs, even though his first Bonneville was a unit-construction machine.
For those wondering, a “pre-unit” Triumph simply means the engine and gearbox are separate components. From 1937, the first year of Triumph designer Edward Turner’s Speed Twin, the parallel twin-cylinder engine and transmission lived in completely separate alloy castings. In 1957, the 350 cc Triumph 3TA gained a unit-construction engine, where the cast alloy cases contained a cavity that housed all the gears and shafts of the transmission, behind the crankshaft. The 500 cc 5TA featured unit construction when it was launched in 1959, but the 650 cc models didn’t get that treatment until 1963.
For Klassen, a retired mechanical engineer, the beauty of a Triumph lies in the pre-unit machines, and, as mentioned, he’s built a few, including a Triton, a desert sled and several bobbers.
Triumph’s Duplex Frame
A seed had been planted, and Klassen began thinking that building a close-to-stock 1962 Bonneville, with the duplex frame, would be something he’d like to do. The project didn’t really gain any momentum until he was visiting John Oland of Motoparts in Edmonton.
“I was wandering around and went out into John’s boneyard, where there was a row of frames,” Klassen explains. “I spotted a duplex front frame loop, and it had surface rust on it. I spent a few more minutes examining it and
discovered it didn’t have a VIN stamped on it. Also, the side-stand and centre-stand lugs had no evidence of use – I think it was a factory replacement frame that had never been used.”
The Search Begins
On eBay, he sourced a number of specific parts to piece together the duplex front forks. These have different internal damping components from earlier pre-unit forks, and the triple trees also differ.
While working on the forks, Klassen was on the search for a set of duplex frame T120 Bonneville engine cases. He found a set on the Canadian Vintage Motorcycle Group’s buy-and-sell web pages and purchased them out of Ontario.
“There’d been some alloy repair work done to the drive side case, where it had cracked about two or three inches below the base of the cylinder,” Klassen says. “The repair had been done years before, and I re-profiled the outside
of the case while Derek (Pauletto of Trillion Industries in Calgary) welded up the internal cracks.”
With a set of usable T120 cases, Klassen located a used crankshaft that he cleaned up, then checked the balance factor and had the journals ground to accept new shell bearings for the connecting rods. He sourced a set of standard bore cylinders from a friend, and bought new Hepolite pistons and rings from Motoparts.
Luckily, the Bonneville alloy twin-carburetor cylinder head was a piece Klassen had in his own collection of parts. It was rebuilt with new guides and valves, and the seats were freshly cut. A set of Amal 376 monobloc carburetors were vapour-blasted to remove the exterior surface oxidation, and attention was paid to the internals during careful reassembly.
The pre-unit gearbox was also on Klassen’s shelf. It was disassembled, cleaned and checked for any issues. Nothing major was amiss, so it was carefully reassembled and sealed up for use in the Bonneville.
The Search for Rear Suspension
Meanwhile, after searching for months for a duplex rear sub-frame, Klassen turned to his plan B. He knew from having built his duplex frame bobber that a unit Triumph hardtail bolted right onto the duplex front frame loop. If a unit hardtail would fit a duplex frame, then why not a unit swingarm sub-frame?
Klassen began looking for a unit swingarm rear sub-frame and found one locally in a friend’s garage. At some point, the rear seat hoop had been cut off, so the first thing Klassen did was bend up a new tube and make frame plugs so it could be welded into position. Several mounting tabs were cut away, and he proceeded to hand fabricate new studs and tabs to hold the parts unique to the duplex frame, including the rear brake pedal, oil tank and battery/toolbox. With the brackets cut and shaped, Klassen had them all welded in place by Cory Brewster of Brewster West Industries in Turner Valley before all frame components were powdercoated semi-gloss black at Rite-Way Powder Coating in Calgary.
A set of new Hagon shocks went between the sub-frame and swingarm, and Klassen turned his attention to wheels. For these he wanted to use flanged alloy rims. At a Red Deer vintage motorcycle swap meet he found a WM2 19-inch for the front, and at the Millarville swap meet, he unearthed a WM3 18-inch, both in a 40-spoke pattern. The front hub is a later-style eight-inch Triumph item, while the rear is a stock Triumph spool-style. Klassen ordered stainless steel spoke sets from Walridge Motors, and with the hubs powdercoated semi-gloss black by Rite-Way, he laced and trued the wheels himself and installed Dunlop Gold Seal tires front and rear.
Only when the Bonneville was mostly complete did Klassen start searching for a gas tank.
A Rare Fuel Tank
“It’s hard to find an original duplex gas tank,” Klassen says. “You can get a reproduction tank out of India, but I preferred original metal. When I built the duplex bobber, I bought a few pieces off a fellow in Ontario, so I called him and asked if he might have a duplex tank.” Although he struck out, the fellow directed him to Ken Brown, whom Klassen describes as “a Triumph restoration guru in B.C. Ken had a stock Bonneville gas tank for the duplex frame that he was willing to part with, and it came with the badges and the parcel rack.”
When it arrived, Klassen was pleased with its condition. As sold, it had been cleaned and left in a coat of primer. Scott Wilson of Calgary (regular readers might recall his Shinobi Honda CB450 build story – April 2018) was entrusted with the two-tone paint job on the tank and the gloss black on the oil tank and toolbox.
Fenders were sourced from eBay sellers: the rear a chrome guard that needed some modification to allow the grab handle to fit; the front is also chrome from an unknown application. Klassen made up the front fender stays using lengths of 3/8-inch steel tube with cast end pieces harvested from a set of unit Triumph stays.
During mock-up, Klassen fit a set of one-inch-diameter low bars, but didn’t think they suited the look of the Bonneville. He opted instead for a set of Norman Hyde M-bars, and the rider’s view is complemented with a set of Smiths chronometric instruments, including speedometer and tachometer.
All fasteners were cleaned, glass-beaded and sent to Victoria Plating for cadmium coating during final assembly. One of the last pieces Klassen sourced was the grey-topped saddle from Walridge Motors. And, after seeing a photograph of a leather Triumph tank-top bag in Lindsay Brooke’s book Triumph Motorcycles in America, Klassen cut and hand-stitched his own version.
It’s a Runner
With final details in place, the machine fired first kick thanks to a strong spark from the Lucas magneto that Klassen had cleaned and serviced himself. There was, however, a jetting issue that had to be overcome before the Bonneville became a reliable runner – it’s now covered just over 800 km this past summer.
“The handling of a duplex frame bike is so much different than any unit or earlier swingarm frame pre-unit Triumph that I’ve ridden; it has a much better feel,” Klassen says. He liked it so much, in fact, that he “decided to sell my 1970 Bonneville – it’s found a good home. The duplex Bonneville was a three-and-a-half-year build because finding so many of the parts took time, but the result was worth it.”
