It’s been a long time since we reported on progress from Ferg’s workshop, as he builds a bike hopefully capable of taking the Southern California Timing Association’s 650cc Pushrod Production Class speed record.
The Triumph Bonneville assembled and on display.
The main reason has been the ‘two steps forward, one step back’ nature of developments. Examples include the lightweight Kibblewhite valve train, around which the entire cylinder head was re-configured and gas-flowed. Expert engine builder Graeme Cole determined that the springs – developed for 1/4 mile drag racing – were too strong for prolonged high-speed use, so standard Triumph springs were installed instead. This required new collars and keepers to suit the thin-stem valves, one of many tricky jobs handled by James Simpson Engineering.
The Triumph Bonneville in the workshop under assembly.
Perhaps the biggest, and certainly the saddest, issue was the passing of both Graeme’s parents in very close succession. Graeme soon got back to work however, and the engine was reassembled with all its new parts and meticulous attention to detail. If it runs the way it looks, that record is a done deal.
The Triumph Bonneville engine reassembled.
The engine was slipped back into the frame in February in time for an appearance – as a whole motorcycle! – in the display marquee at the NZ Classic Motorcycle Festival at Pukekohe. The bike attracted a huge amount of attention, even surrounded by a gallery of rare classic race bikes. The many chats with enthusiasts provided an opportunity to acknowledge the ongoing support received from Auckland Motorcycle Club.
The Triumph Bonneville on display at the NZ Classic Motorcycle Festival.
Back from the Festival, attention turned to getting the ancillaries ready to restart the motor, with a new loom created and wired in under the expert eye of Rob Mackichan. Things were getting close…
One bodge begets another
If there’s a nugget of wisdom to impart about building up a 50-year-old bike for racing, it’s this: never trust that any part you take off the bike a) belongs there, b) is the correct part, and c) functions, even when things appear to be working. This much became clear when attempting the apparently simple task of reinstalling the rear wheel and fitting a new chain.
A side-by-side comparison of sprockets.
Plan A was to install substantially higher gearing to, hopefully, maximise the top speed. A two-tooth-larger front sprocket was installed as part of the engine build, and a new 43-tooth hub was sourced for the rear. Unlike modern machines with bolt-on sprockets, the Bonneville’s rear sprocket is a part of the hub. It came with a 46 that was bolted to its hub, while the 43-tooth replacement was integral.
The rear wheel with sprocket and pivot.
Fitting the brand-new, shortened chain revealed a few oddities, like the chain ‘picking up’ on the sprocket rather than sitting snugly down into the recesses. Was it the wrong pitch? A side-by-side comparison with the old hub revealed that the teeth were much wider, the likely cause of the poor fit.
Ah well, back to the old hub which will do fine for running in and testing. Except, the brake pivot was fouling the end of the chain adjuster. No problem, fit a longer torque arm and move the pivot round and up a fraction out of the way, right?
The hacked off chain adjuster.
After a good ponder, the clues all started to fit together. Why was one chain adjuster hacksawed off short? Why was a non-standard torque arm fitted? Why did the adjuster nut foul on the brake pivot? It turns out, the old hub was totally worn out. Rather than replace this $200 item, a previous owner had shortened the torque arm, pulling the brake pivot down a fraction, giving longer throw on the brake adjustment. Then they hacked the end off the adjuster’s thread to make room for the pivot. Genius.
The split fuel tap.
All of which means the team has to sort another hub and, possibly, a slightly smaller sprocket to go with it. Just another thing to add to the parts list which also includes a new fuel tap after one of them decided to split in two during removal–better to have that problem now than on the salt flats of Utah.
Despite the issues, there has been progress. The throttles have been connected up and new temporary fuel pipes have been installed (proprietary ones demanded by SCTA rules are being sourced for racing). Gareth From GT Auto Electrix in Hillcrest fitted waterproof (and salt proof) connectors and conduit to the electrics, wired in the mandatory kill switch and connected up the Dynojet air/fuel ratio logger to the lambda sensor. A host of clever fixes have been put together by James Simpson Engineering of Albany, including a removable exhaust balance pipe block-off arrangement, plumbing the lambda sensor into the exhaust, fabricating a battery stay and mounting an oil gauge on a handlebar bracket.
The clever handlebar arrangement.
So the countdown to start-up is now on, a process Graeme will be in charge of, then dyno time booked in March. At least two or three dyno sessions are anticipated, using Brett Roberts’s facilities in Paeroa which is handy for Graeme. We’ll definitely have updates on those milestones.
The exhaust, wheel and chain arrangement.
[Spec Box:] Heart of the beast
- Billet crankshaft
- 11.5:1 custom-forged pistons
- Carillo rods
- High lift inlet cam
- Flowed/ported head
- Lightened rockers and collars
- Custom push rods
- Oversize, thin-stem Kibblewhite valves
- Carbs bored to 33mm
- K&N filters
- High-flow oil pump
- Reed-valve crankcase breather
- Seven-plate clutch