Millenium Bonneville

Triumph Flat Trackers

Millennium Bonneville

'This feature originaly appeared in Classic Bike Guide and is copyright to CBG/Alan Cathcart'

Triumph's product-planning group didn't originally set out to simply 'build a new-generation - Bonneville', as rnany will have likely assumed. The team's initial goal when the 9O8MD project was officially launched in early 1997 was to develop an 'entry-level rnachine of medium to large displacement'. The 'entry-level' component of that formula is significant because with the United States and world markets changing so dramatically, and with hordes of new and re-entry riders joining the motorcycling ranks, it was considered vital that Triumph have a competitive player in that category.

What pulled Triumph toward the classic Bonneville direction? 'Triumph's heritage was the key'; says the company's export boss, Ross Clifford. 'Though a V-twin was the obvious option, we decided to develop a parallel engine layout due to the rnarque's 'heritage' aspect' Of course, 'heritage' can be a touchy subject where Triurnph is concerned, especially arnong Brit-bike traditionalists. Still, they do use it, and rightly so. The Bonneville engine tearn had a tough task: to marry rnodern technology with classic engine architecture - and this was a Bonneville, remember, a bike considered by many to be the definitive classic Britbike. The T120 Bonnie is regarded as a fast, decent handling and absolutely beautiful machine; it's a reputation that was a constant challenge to the Bonneville tearn throughout the entire R&D process. Like the engine team, Bonneville stylists and chassis tearn rnernbers had the tricky job of blessing the new Bonnie with thoroughly rnodern function and a look as close to the original Bonneville's as possible - not easy given the rnassive gains in chassis development over the last several decades. So they started from ground zero, importing a fully restored, 1969-spec T120 Bonnie from the States, and using it as a baseline for items such as styling, ergonomics, control positioning, etc. 'The '69' bike embodies the best possible attributes of the old Bonneville', says Clifford. 'We felt it was the right place to start.' A key design brief was that the V machine had to be 'light, agile, and corner well' Prototype parts were arriving throughout the fall and early winter of 1998. The first Bonnie engine ran on December 15, 1998, with little more than a few carb-jetting hiccups. initial engine testing then began, the teams first running the original prototype engine then others through all manner of timed-running and teardown/check phases.

There were a few glitches, but nothing surprising. Endurance testing came next: The engines were run hard for extended periods of time, then torn down to check for wear and/or failures. The main changes made before committing to tooling production were minor: the countershaft sprocket was moved 3mm inboard (to help with peashooter-exhaust packaging), and the crankcase clamping design was altered for improved sealing. Also by the end of 1998, the chassis team had presented the updated styling prototype to upper management and the marketing/sales staffs, and response was positive. The overall look and general makeup Triumph's new-generation Bonneville was now set.

TRIUMPH BONNEVILLE TECHNICAL

As an eight-valve, parallel-twin with double camshafts, the new Bonneville's air/oil-cooler plant is thoroughly modem, though it does share with its pushrod, two-valve-per-cylinder T120 an 360-degree crankshaft throw, with both pistons rising and falling together in the nickel/silicon-plated bores. That's a prime recipe for intrusive vibration Triumph's engine team therefore decided to incorperate twin gear-driven balance shafts located at 2 o'clock&10 o'clock relative to the plain-bearing crankshaft.

The new Bonnie engine also needed to share the T120's power characteristics. The 790cc was thus designed to be 'lazy' rather than 'potent',which the reasonably long-stroke engine dimension 86x68mm help ensure. Ditto the T120 engines look something designer John Mockett had a role in alongside the engine team. Although the new Bonnie's drive-chain was designed to run on the right side of the bike (the T120 runs its chain on the left)several details were designed to keep the basic look somewhat intact, including the finned cylinder & dummy pushrod tube in front of the engine (originally intended to be an oil feed but now acting as a cylinder head oil breather). Although a wet sump design with no separate oil tank (unlike the T120) the new Bonneville engine employs internal oil lines wherever possible to retain a clean appearance,while twin oil pumps and a sizeable oil radiator are fittedfor cooling as well as keeping the plain bearing engine's internals together.

Another ploy in helping endow the new motor with period looks is the Bonneville's cam drive system the centrally mounted chain driven directly off to a set of idler gears in order to narrow the camshaft spread. Combined with dropping the cams in the head to get the pushrod look, this reduces the engine height significantly. Certain period Triumph traits were deemed surplus to requirements, however hence engine's horizontally split crankcases, designed to eliminate the oil stains in the owner's driveway provided by its pushrod ancestor's vertically engine, but why go to all the trouble of having up a DOHC 8-valve design to look right, rather than concoct a more humble, and presumably less costly single-cam two-valver? 'Two reasons', says Triumph's Ross Clifford. 'One was that we're used engines with four valves per cylinder. Another was performance; 55-60bhp was our design target we wouldn't have got that power with two valve heads. We did take a serious look at a six-valves with three valves per cylinder (two inlet,one exhaust) . The cost effectiveness of going to three valves percylinder was marginal, so we opted for four.

9.2:1 compression, the design target was achieved early on, and in production guise the Bonneville delivers 62bhp at 7400rpm, with rnaxirnurn torque of 60 Nm/42 ft./lb as low as 3500rpm. Since it was always intended that the Triumph twin-cylinder family for which the company intends a long production life would comprise only two distinct models - the Bonneville, and another new bike that will appear in due course - there were fewer design constraints on the new engine, with modularity not such a key issue as on other Hinckley Triumphs. But while it was always intended that the company's new twins should be stand-alone products, there was interest in parts commonality with the company's existing three-cylinder products.

Thus, some components from both the older T300 and newer T500 models were used, such as the much-improved T500 six-speed gearbox - well proven on more powerful bikes such as the 955i and TT600, and here used on the Bonneville in five-speed guise - mated to a cable-operated wet clutch. That's because benchmarking the new model with its likely opposition said five speeds, not six - but with a lazy top gear. Unlike other recent Triumphs, the new Bonnie is not fuel-injected, but uses a pair of 36mm Keihin carbs fitted with electric heaters to combat icing, and a throttle-position sensor linked to the Sagem digital ignition to optimise throttle response.

Triumph chose carbs rather than EFi mainly because of the style of motorcycle the Bonneville represents; it's not a sport-bike. Cost was also a factor - though not emissions: Triumph says it can meet all current emissions requirements with carbs, especially when air-injection is used. The period-looking peashooter-type twin exhausts are uncharacteristically long in order to gain the requisite silencing capacity without compromising cornering clearance - the kink in the pipes helps pull them out of harm's way. With the engine such a kcy component of the born-again Bonnie in styling as well as mechanical terms the chassis team had to plan far ahead since, for the first time on any Triumph, the Bonneville's steel swinging arm pivots in the engine crankcases as well as through steel chassis forgings ,in the interests of rigidity .

The T120 was swiftly rejected as a design benchmark apparently it was quite alarming how unstable test riders could persuade it to get at high speeds! Triumph had a 115-mph target for the born-again Bonnie, which the new bike amply fulfils in production guise, and it has been proved in testing to be stable in turns at that speed, even with a passenger. The engine is solidly mounted in the frame at five spots, with counter-balancers removing the need for rubber mounts. ln fact, Triumph engineers have dialled some vibration back in by altering the bar weights to restore a little 'character'. The cylinder head is braced to the headstock to add extra stiffness, and twin front downtubes pick up the engine at the front.

In keeping with the maniage of opposite design goals, twin Kayaba rear shocks adjustable only for preload are fitted in a semi-laydown position,that Tnumph says represents a compromise between the retro-upright look of the T120, and the modern slanted position of a twin-shocker like the CB5OO Honda. These are matched to non-adjustable 4mm Kayaba telescopic forks, set at a kicked-out 29-degree head angle, with 117mm of trail. Connecting them is a spine frame redolent of the early range of bikes from the Hinckley era. 'Stability was key, as well as the retro look and the company has a good reputation for building solid-handling bikes', says Clifford. 'We wanted our new-generation owners to experience the satisfaction of light steering with secure handling, hence the spine frame'. This employs a 19-inch front wheel and 17-inch rear the bigger front primarily to get the look right with modem lower-aspect 19-inch front tyres, Bndgestone tyres are fitted, the front a 100/90R19 and the rear a 130/80R17. The long,58.8-inch wheelbase and relatively low 30.5-inch seat hight - an inch lower than the original T120 - emphasise the lean appearance of a 205kg/4521b motorcycle on which shorter riders should feel at home, and which will be offered only with a sidestand (though with an optional centrestand), and with a flat handlebar fitted as standard. Unlike the old days there will be no high-rise option for North American customers.

A single 3lOmm front and 255mm rear disc, each gripped by two-piston Nissin calipers, are fitted; Triumph says it decided not to fit a second front disc for both styling and cost reasons. Equally, a rear drum was never an option: "We benchmarked the smaller W650 Kawasaki in terms of stopping power, which we've achieved, and for our target rider the rear brake is important', says Clifford. 'That's another reason why there's no provision for a kickstart - our projected customer base looks for convenience over period quirkiness. This is a modem motorcycle in period dress, with all the attributes which this entails: That it is, And after waiting patiently for a decade while John Bloor and his men brought Tnumph back from the dead and secured the company's future, traditional enthusiasts can now welcome back one of motorcycle history's best-loved models, in vastly improved guise - all for a projected sum of about £5500 in the UK, or $7000 in the USA, where 70% of the total annual production of 4000-5000 bikes is likely to be headed.

The same, only different...

Triumph Flat Trackers

Dave Boyer makes street legal dirt track Triumph's for a simple reason."They're fun to build fun to ride and easy to handle,"say's the Florida based Bike Builder.

Dave calls his concern Specialised Motor cycles and has built 12 street legal bikes with another 12 to complete."I only do work for a few people mainly friends", says Dave.

If you like what you see and would like something similar ,contact TDR restorations who supply the full range of parts and can modify your machine for you.Visit TDR restorations in the SHOP on this site to purchase or view their most popular parts.

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