When we recently popped round to see Ferg’s 1970 Triumph T120R Bonneville, the ‘bike was just a collection of components. The frame and other cycle parts had come back from the stove enameler’s, with some less showy items treated to a coat or two of rattle-can black. The forks were about to go away for a specialist rebuild (apparently specialist tools are needed, so it’s as cost effective and less work to get it done).
Once those were completed, the next milestone would be assembling the rolling chassis. The engine, meanwhile, was in two different places: the top half out for combustion chamber work and an entirely new valve train; the bottom half away with Bob the Balancer, along with some trick Carrillo rods to fit to a new billet crank.
A heavy secret
Weight might hinder acceleration but it’s almost entirely aerodynamic drag that reduces your top speed. At Bonneville another factor comes into play: the salt. Racers are always fighting for traction. Wheelspin, or slippage, means you can’t convert all your power into forward thrust, and it can cause frightening instability.
The answer is ballast. Weight towards the rear aids both traction and stability. The problem in a production class, like the one Ferg is set to race in, is the demand for originality, at least in appearance. So strapping on lead weights is a no-no.
You can, however, add weight where it’s not visible: what the eye doesn’t see, the scrutineer doesn’t fail. For a production ‘bike the accepted solution is to fill frame parts with lead shot, biased towards the rear. Carefully drilled access holes, and a clever arrangement in the main frame tube, will allow Ferg’s bike to carry the best part of 20kg of the stuff. But only that first run on the salt will reveal whether it’s enough and located in the right place.
In the meantime, Ferg is working out just how much disguise the ballast addition will need to remain undetectable to the naked eye. Apparently, if you do get a record the authorities impound the ‘bike, take the head off then measure up the engine dimensions. And–in production class–refer tightly to the original workshop manual, which competitors must supply themselves. A small discrepancy from what’s shown in the book could mean disqualification.
Although Ferg’s garage is full of carefully organised and labelled parts, noticeably absent on this early summer’s evening was anything to do with the unit-construction 650cc twin. That’s because the cases are away being machined for new ball-race bearings and a later model stator, before accommodating a brand new billet steel crank. The latter, due for finishing in a week, took three months to make. Identical to the original, it would be perfectly balanced and much stronger. No knife-edging was required because the Triumph is a dry-sump design. Clamping the crank will be American-made Carrillo rods, a familiar name in tuning old British ‘bikes. Apparently no longer obtainable, Ferg sourced his set with a ‘phone call, off a shelf in a mate’s shop in England. With everything, including pistons, pins etc. weighed and balanced by Bob Mead in Auckland, the bottom end will then be complete.
Up top, meanwhile, Dean Landon of Landon Motorsports has been weaving his magic over the engine’s breathing apparatus. In the last instalment, we mentioned the $1,000-worth of valve-train components that had just arrived from America. Sourced from Kibblewhite, the kit includes larger valves with narrower stems, narrower valve guides and specially-designed ‘beehive’-shape valve springs designed to reduce ‘float’ at high revs. Kibblewhite are a big name in valve-trains for motorcycle sports in the USA, especially drag racing. The big valves, pumping at high speed, should help with all-important flow in Bonneville’s thin air. But getting the most out of them requires serious work on combustion chamber design, different cams and even changes to the valve angles. And that’s what Dean Landon has been up to. “When he talks to me about what he’s doing, he descends into Mechanical-Engineering talk,” says Ferg. “Which means I don’t understand a thing. What I have learned is that basically, if you want your Triumph to go fast, you throw away the top end and start again.”
Once Dean has completed his work, including the installation of a full-race inlet cam and a half-race ‘Thruxton’ exhaust cam, the engine will be given over to Graham Cole for final, careful assembly. The objective is a top speed tested here in New Zealand of 130mph. When Ferg got hold of it, it managed 106mph, which is almost exactly the Bonneville record. But that’s on salt, at over 4,000ft. “The rule of thumb is you’re down about 20% on power at that altitude,” advises Ferg. “I talked to the tuner of the bike that set the record at 106mph, and he said it had about US$50,000 or work done on it. So we're breaking new ground here.”