Think Big A Beastly Cbx1000 From Purpose Built Moto

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There’s never a quiet moment for Tom Gilroy and the team at Purpose Built Moto in Queensland, Australia. Tom started his career fixing up old bikes in a shed on the family farm; today he runs a bustling custom business with a prodigious build output, a store full of parts, and he’s even made a film on the side.
He’s probably seen it all, but he still gets the occasional chance to try something new. Like the job he’s just finished on this slightly scary CBX1000.

“We get a few projects every year that really make me step back, and take stock on what we’re doing,” says Tom. “This CBX1000 is one of those builds. When Honda released this six-cylinder in 1978, it got a lot of people talking: it was not only the fastest production bike ever made, but also an engineering feat.”
With DOHC, a 24-valve head and a solid 100hp at the crank, the CBX1000 is a beast. But it’s also mired in the 80s. “Our rider Luke loved his 1981 CBX, but it was getting tired,” says Tom. “The bike was due for a re-fresh, a re-build and a re-think.”

Client Luke is a big guy, and he likes big bikes. He also wanted to drag the CBX out of the 80s and give it a healthy dose of modern styling. After going through PBM’s portfolio, Luke and Tom found a few areas of common ground, and started to develop a style for the CBX.
“Luke was our ideal customer. He came to us with an idea, but trusted the team to do what we do best—build one-of-a-kind motorcycles to be ridden, enjoyed, and stared at.”

The Honda took shape as a sharpened-up café racer, retaining the CBX’s bold tank but adding modern suspension, wheels and performance upgrades. “We wanted to bring out the power the engine already had,” says Tom, “but make it more ‘in your face’—by stripping off weight, and boosting the handling.”
After the tear down, the CBX was already looking better. “This bike is a Pro-Link model, with an aluminum swingarm—and a huge front fairing that weighs as much as a bar fridge,” says Tom. “It dropped 20kg with the removal of six bolts!”

As Tom started to measure up the CBX1000, he realized that it wouldn’t be possible to meet the owner’s request for modern sport bike tires while using the stock swing arm. Before he started cutting, he had to go shopping—and landed on a set of second generation Suzuki Hayabusa forks, and a 2010 Aprilia RSV4 swingarm and suspension linkage.
Alloy wheels wouldn’t cut it either, so Tom installed a set of JoNich M9 rims, each with 24 spokes. (“The all-black wheelset, with a sparse arrangement of 9mm spokes, gives the Honda an ultra modern edge.”) The wheels are finished off with new Moto-Master rotors all round, plus a custom-machined aluminum sprocket.

The Hayabusa front end was an easy fit with a custom triple clamp. Tom’s added mid-rise ProTaper Contour bars in a ‘Carmichael’ bend, new brackets for the gauges and Flashpoint LED headlight, and clean modern switchgear. Running lights mounted on either side of the mighty CBX1000 motor add a little street fighter flair.
To properly integrate the swingarm, PBM decided to completely rebuild the subframe and seat section. Everything behind the engine cradle was removed, the RSV4 swingarm was pinned in place, and Tom started to mount the lower suspension linkage.

“The idea was to make the top suspension mount as seamless as possible. By using the brace on the tail frame, from one side the shock mount isn’t visible at all.” It permits a 180 x 17” rear tire too, but the real upgrade comes in the form of the custom-built Öhlins TTX rear shock—“dialed in at Ride Dynamics for an unbelievable feel on the bike.”
The tail is a little different to the usual hoop design seen on most customs. It houses the battery, starter solenoid and a set of three LED mini stoplights, flanked by PBM’s own Hollow Tip 3-in-1 tail lights.

The tank was starting to rust out, so it’s been stripped and repaired, with a few of the seat mount sections smoothed out, and a pop-up filler cap was welded in. The last piece of fabrication was on the front fender: “It’s aggressive, but exactly what the front end needed.” The paint is simple but extremely effective: a matte Grey, with pops of orange detail.
The top end of the engine was freshened up and a new set of Keihin FCR carbs bolted on, breathing through DNA filters. The donor bike already had good performance headers; the only problem was the six mufflers were too long. So, on went six PBM torpedo mufflers, with custom mounting brackets.

The sound, as you can imagine, is incredible. “It’s like an old Formula 1 engine as it climbs through the rev range,” says Tom, “without being overbearing while you’re racing down the road.”
All of these mods were tuned to perfection at Dynomite Moto, with the CBX now putting out 100 hp at the rear wheel rather than just the crank. And this CBX has a revised dry weight of only 228 kg [502 pounds], down from a cruiser-like 277 kg [610].

“The first ride on this behemoth was intimidating,” Tom admits. “It’s such a wide motorcycle. But once you get moving, the bike is surprisingly nimble through corners and holds the road incredibly well. The engine starts to liven up above 4000 rpm, then it kicks like a mule and you won’t know what hit you!”
Luke already has a new project in mind for Purpose Built Moto: an even more intimidating Suzuki GSX1400. But until then, check out Tom’s video rundown of this CBX1000—which shows exactly what goes into building a bike at this level.
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