1982 Honda CB900
PURPOSE Built Moto is a Gold Coast custom bike shop determined not to be pigeon-holed into a single style. As well as the usual crop of trackers, cafe racers and scramblers, recent builds include a highly-modified Ducati GT1000 sports classic and an even more radical Harley Sportster adventure bike! And then there’s this tres-cool chopper built around a twin-cam Honda CB900 Bold’Or.
“This bike being my first foray into the chopper/bobber style set, I’m thankful to owners John and Carol for having trust in my skills as a designer and builder to carry my ideas onto their bike,” says Purpose Built Moto’s main man, Tom Gilroy.
“I draw inspiration from a lot of things, least of all other custom motorcycles. During the time where I collect my ideas I’ll shut out most outside influences of custom bikes, and other builders. These days we’re constantly barraged with photos from the internet of exactly what everyone else is building. I’ll instead think of the rider, where he’s taking the bike and what I want him to experience on that ride.
“It sounds a bit left field but that’s my honest process. I search for inspiration through other art forms, and try to take an introspective approach to each bike. “Switching my head out of building more practical and minimal cafe racer and scrambler-style bikes was my biggest challenge. Generally, on my projects each part or piece serves a purpose and that’s why it’s there. On this bike, I found myself creating more ornate ways to get the job done. Instead of making things minimal, I would make parts more elaborate and showy, just because that’s what this bike is about.”
John had purchased the 1982 CB900 as a wreck 10 years ago, with plans to have it built into a chopper. A resident of western Queensland, he sent it to another custom shop but was underwhelmed with the result when it was finally completed many years later. “It didn’t run properly and was a mess of poor design,” Tom says. “Nothing lined up or worked properly, not even the chain and sprockets. On pulling it down I found a nest of wires under the seat, some of which I couldn’t even make sense of. The exhaust was also a nightmare, with a fourinto-one collector that looked like it was pulled off a Daihatsu.
1982 Honda CB900 engine: Air-cooled inline four-cylinder fourstroke; chain-driven DOHC, four valves per cylinder; 64.5 x 69mm for 901cc; 8.8:1 comp; 4 x Keihin CR smoothbores; electronic ignition; custom four-into-four pipes; multi-plate clutch to five-speed transmission; chain final drive; 95hp at 9000rpm (stock)
“I couldn’t let this bike go back to its owner without it being the envy of any redblooded man in his hometown. I wanted it to be right, and something John would be proud to ride and show off to his mates.”
First step was to strip the bike and address the stance and overall look. The custom frame had at least been wellfabricated and has been retained apart from the rear end, which was redone to better suit Tom’s emerging idea of what a swingarm chopper should look like.
“This whole process was foreign to me,” Tom says. “I had to consider a new set of geometry dynamics to achieve a good and solid chopper look. If I had built the bike from scratch, the backbone would have more of an angle down to the rear wheel to create an arc back up over the rear wheel when building a seat. Working with what I had, the tail was rebuilt from 28mm chrome-moly tube, and some new shock mount spigots turned up. This created a shorter sharper look for the tail. The rear swingarm was also shortened about 50mm to tuck the bike up more. The stance was finalised with a set of shrouded 10-inch shocks supplied by Ride Dynamics.”
1982 Honda CB900 chassis: Fabricated duplex chassis in tubular steel; custom chrome-moly sub-frame; conventional CB900 forks with custom top triple clamp, dual 280mm rotors with twin-piston calipers on laced 21-inch rim; shortened CB900 swingarm with dual 10-inch shocks, single 297mm rotor with twin-piston caliper on laced 17-inch rim; Avon Cobra tyres
The rear 17-inch wheel was retained but the front 19-inch wheel was laced to a 21- inch rim, both sporting Avon Cobra tyres. Forks are stock CB900, as is the lower triple clamp, while the top clamp was replaced with a CNC-machined custom clamp in the style of a vintage Ceriani unit.
Stance addressed, Tom turned his attention to the bodywork and details that can make or break any custom bike. “The huge Mustang chopper tank had to go,” he says, replaced with one from the original early 1970s SOHC Honda Four. “The tank and paint scheme were pillaged from a K3 CB750. I liked the shape, it fitted with my ideas for the bike and it lets the big 900cc engine protrude out the sides and gives the rider a great sense of scale on the engine he’s riding with.”
Down back, Tom fabricated a huggerstyle lipped mudguard and custom sissy-bar—both of which move with the swingarm—on which he mounted a prototype of his own Mini Orbit taillight. The seat was shaped and finished in Nubuck black leather with linear stitching by Jamo at Timeless Auto Trim, after which Tom relocated the footpegs.
“With the rider’s seat taken care of, we needed to find a place for his feet,” he says. “The previous pegs were far too rearward for any comfortable ride. I wanted the CB to be able to take long strolls so I set about mounting some bolt-on peg mounts either side of the motor to house the Tarozzi pegs, shift linkage and Brembo rear master cylinder.”
Up front, two Purpose Built Moto 4.5- inch Flashpoint headlights are mounted vertically in classic chopper style. Low ape handlebars have been narrowed 30mm and are fixed with one-inch brass clamps. The uber-clean rider’s eye view has been achieved with inverted brass clutch and brake levers and PBM’s own minimalist button switchgear, and by relocating the now cable-operated Brembo front brake master cylinder under the fuel tank. A small speedo is mounted low on the left side of the tank.
“Looking at this bike in bare metal, fabrication completed, it was something very different from anything I’d done before,” Tom says. “It was time to get the vision completed with some paint. Very early in the piece I had decided to run with a CB750 K-model tank painted in candy red and gold leaf. This would tiemy brass bar work in, and give it the eye candy appeal I wanted. It would also ruffle a few feathers with purists seeing a nice CB750 tank on a bastardised Honda chopper. Just quietly I love revving the old blokes up! Justin at Popbang Classics really nailed the paint.”
Luckily, the engine was in good nick. “The engine once pulled down showed it was fine inside, clutch and gearbox were great, so we locked it back up. The only upgrade to the performance was a set of Keihin CR carburettors and DNA performance pod filters,” while the ‘Daihatsu’ exhaust was ditched for fourinto-four pipes finished with turned brass exhaust caps. The engine was finished in a fresh coat of black paint before the whole lot was dyno-tuned by Dynomite Moto.
“It’s obnoxious and loud, but so is your shitty Harley so deal with it,” Tom laughs. “It’s a reasonably light bike now and is surprisingly fast. The 900cc give it enough pull to get off the line, but if you want to feel a rush, crack that throttle open and let it pull past 4000rpm and it really shows you what it’s made of. The thing just won’t stop pulling!
“The bike holds a big presence on the road. It’s loud, bright and a joy to ride. It doesn’t corner like a demon, but the pegs and pipes allow enough tip angle to bring a big wide smile as you point it through and open the Keihin carbs up.
“Something I’d never understood until now was the allure of riding a chopper,” Tom says. “I’ve always loved winding roads, fastpaced 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. The excitement is all in the novelty, and this strange imagining of a CB900 has yards of it.
“If you want a performance bike, go to a dealership and buy one. This CB900 isn’t practical, what it does provide is a thrilling and visceral ride. It’s noisy, raw and obnoxious, and that’s totally OK for a motorcycle to be that way.”