Chopper Rescue: A CB900 revived by Purpose Built Moto

Honda CB900 chopper by Purpose Built Moto
We don’t often go in for choppers around here—but we do appreciate the skill and effort that goes into building a truly stellar chop job. And Tom Gilroy at Purpose Built Moto on Australia’s Gold Coast gets it too.

The PBM portfolio is stacked with cafe racers and scramblers, but that didn’t stop them from tackling a chopper…and knocking it out the park. “The skills are the same,” says Tom, “and I love the style just as much—it’s just a different thought process.”

Honda CB900 chopper by Purpose Built Moto
Purpose Built Moto worked with an unusual donor bike for this project: a Honda CB900. And one that came with its own baggage, too.

The shop’s client had bought it wrecked, ten years ago, and decided to have it rebuilt as a chopper. He originally found a builder on the Sunshine Coast—but the work took literally years to complete, and the bike looked horrible and didn’t run right.

Honda CB900 chopper by Purpose Built Moto
“He was never happy with it,” Tom tells us, “which, after waiting so long, is understandably a kick in the guts. One thing I will say, is that the frame that was build from scratch was very well fabricated, an amazing job.”

PBM decided to build their own take on a Japanese chopper: “Something the owner would be proud to ride and show off to his mates.” So they stripped the bike down, ripped out the dodgy wiring and got cracking.

Honda CB900 chopper by Purpose Built Moto
First on the agenda was the CB’s stance. Tom and co. kept the 17” rear wheel the bike had come with, but re-laced the front hub onto a 21” rim. Both are wrapped in Avon Cobra tires.

Since the Honda’s frame had been done well the first time around, Tom focused his energy purely on rebuilding the rear section. “This whole process was foreign to me,” he says. “A new set of geometry dynamics to work with, to achieve a good and solid chopper look.”

Honda CB900 chopper by Purpose Built Moto
A new subframe was fabricated using 28 mm Chromoly tube, and a pair of new shock mount spigots turned up. Then the swing-arm was shorted about 50 mm to tuck the rear end even more. Finally, Purpose Built Moto mounted up a set of shrouded 10” shocks, from Ride Dynamics.

Next up, the crew turned their attention to the bodywork. The CB had come with a huge mustang chopper tank—but Tom thankfully swapped it out for a Honda CB750 K2 unit. “It fitted with my ideas for the bike, and it allowed the huge engine to protrude from under the tank,” he explains.

Honda CB900 chopper by Purpose Built Moto
Then came the trickiest part: getting the balance of the seat, rear fender and sissy bar just right. Tom started with a lipped rear fender, then bent up some bar with a trio of curved ends that match the fender’s lip. The arrangement was finished off with a prototype tail light that’ll be joining Purpose Built Moto’s extensive parts catalog soon.

Tom then whipped up a new seat pan and electrics tray, and shaped up the foam. Jamo at Timeless Autotrim kicked out a sublime nubuck leather cover, with pleats that run all the way over the back of the seat.

Honda CB900 chopper by Purpose Built Moto
Up front, Tom designed a vintage style top yoke, taking inspiration from vintage Ceriani parts. That design was then CNC cut and polished up, and now holds a set of narrowed 1” mini-apes.

Purpose Built Moto usually focus on simple and clean results on their cafe racer builds. But for this bike, Tom deliberately wanted to add some flair. “For a chopper, I’m thinking, ‘What is the best looking, and most elaborate way, to get this job done?’”

Honda CB900 chopper by Purpose Built Moto
A lot of this approach translated into the Honda’s intricate new headlight mount. Tom bent up a set of rods that flow up over the yokes, and end in a ducktail that matches the sissy bar’s. The arrangement holds two 4.5” Purpose Built headlights.

The detail work on this chop-job could fill volumes. The cockpit features leather wrap grips, modern Purpose Built Moto switches with internal wiring, and reverse levers with a cable operated master brake cylinder hidden under the fuel tank. And there’s a whole bunch of smaller brass parts scattered throughout the bike.

Honda CB900 chopper by Purpose Built Moto
The horrid exhaust has been ditched too. In its place is a four-into-four system with straight through cans, finished with turned brass end caps. “It’s obnoxious and loud,” admits Tom.

The engine was cleaned up and refinished in black with some mild polishing in places, and treated to a set of Keihin CR carbs with DNA filters. Then the whole setup was run and tuned by the team at Dynomite—so it runs like a dream now.

Honda CB900 chopper by Purpose Built Moto
Tom admits that this bike doesn’t corner as hard as PBM bikes normally do, but it’s still a joy to ride.

“Something I hadn’t understood until now was the allure of riding a chopper. I’ve always loved winding roads, fast paced corners and a bike that handles great. But on this bike, it doesn’t matter where you’re riding, it’s about what you’re riding.”

Honda CB900 chopper by Purpose Built Moto
It also doesn’t hurt that the paint job is flawless. Tom chose red as a nod to the original CB900, then Justin at Popbang Classics laid it down with a deep candy finish, and gold leaf accents.

Not surprisingly, Purpose Built Moto’s client is over the moon with his revived chopper. But more than that, Tom is stoked that someone trusted him enough to step outside of his own comfort zone.

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