When we recently popped round to see Fergs 1970 Triumph T120R Bonneville, the bike was just a collection of components. The frame and other cycle parts had come back from the stove enamelers, 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 its 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 its 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 cant 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 its not visible: what the eye doesnt see, the scrutineer doesnt 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 Fergs bike to carry the best part of 20kg of the stuff. But only that first run on the salt will reveal whether its 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. Andin production classrefer tightly to the original workshop manual, which competitors must supply themselves. A small discrepancy from whats shown in the book could mean disqualification.
Although Fergs garage is full of carefully organised and labelled parts, noticeably absent on this early summers evening was anything to do with the unit-construction 650cc twin. Thats 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 mates 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 engines 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 Bonnevilles 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 thats what Dean Landon has been up to. When he talks to me about what hes doing, he descends into Mechanical-Engineering talk, says Ferg. Which means I dont 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 thats on salt, at over 4,000ft. The rule of thumb is youre 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.