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One Piece at a Time

February 13, 2019

Some builders find the exciting part of a restoration is the hunt for parts.

Story by Greg Williams

Photos by: Bob Klassen

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

1962-TriumphNone of these projects began as complete machines. Instead, a frame came from one location, an engine – or engine pieces – from other sources, and all of the ancillary components from myriad sellers.

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

1962-Triumph-EngineIt was in 2011 that Klassen constructed a bobber based on a 1962 duplex Triumph front frame loop, David Bird hardtail and Bonneville engine cases. During this process, he learned two things: first, he loved the look of the three-year-only duplex frame (Triumph debuted the duplex frame in 1960 and dropped it in 1962) with its twin front downtubes; and second, “Even with a rigid frame conversion on the duplex frame, I felt it handled way better than any other Triumph – unit or pre-unit – I’d ever built.”

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

1962-Triumph-tail-lightKlassen bought the front frame section and began, as he says, a very slow process of acquiring, restoring and building up the parts to make his ideal Bonneville.

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…

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