Purpose Built Moto builds a 700cc vintage twin café…
Tom Gilroy of Australia’s Purpose Built Moto has climbed into the elite echelons of the custom bike world over the past several years, and his Signature series puts his creativity, expertise, and style on full display.
Previous Signature builds such as PBM’s CX500 café racer and Sportster scrambler had a markedly modern edge, but with this ’73 Yamaha XS650 — a former racer — Tom went for a much more classic look, feel, and riding experience:
“This XS650 represents my collective experience and learning on what a classic motorcycle should mean and feel like for a rider.“
The design brief called for an XS650 café racer that could do triple duty as a show bike, street bike, and even handle the odd track day — quite the challenge indeed. What’s more, Tom was striving for a classic, enduring design that could stand the test of time:
“I worked at creating a timeless piece that would feel at home for a rider young or old. Something that people across a family’s generations could be enamoured with.”
The donor XS still had some neat period-correct bits from its old track days, such as an original tank with flip-up fuel filler and Marzocchi rear shocks, which Tom made sure to retain:
“There are vintage piggyback units that were hydroblasted, rebuilt, and internally customised to perform a little more like a modern shock while keeping that beautiful classic racer styling.”
The bike is now rolling on 18” Borrani rims laced to the original rear drum hub and a quad leading shoe 230mm Robinson front drum, completed with 38mm Ceriani forks and custom yokes. But there’s than meets the eye with the front drum — it’s actually a hydraulic setup!
“The front forks are the disc brake model, which allowed me to have the mounting points I needed for the most exciting idea I had for the project. In the past I’ve been left underwhelmed by the performance of cable-operated drum brakes. To address this I wanted to build a hydraulic drum set up, but keep the traditional look of the Robinson drum.”
Tom fabricated a pair of brackets / covers that house the hydraulic actuators behind the forks, and the bike is also running a hydraulic clutch conversion using a Ducati GT1000 slave cylinder.
The frame was stripped down, the factory welds smoothed, and the rear shortened before it was all nickel-plated. The bike is now sporting “mild” rearsets with custom brackets and shifter linkage.
The engine received new internals, a ported head, 700cc Hoos Racing kit, Shell #1 Cam, Mikuni VM34 carbs, and nickel-plated cases. With some light tuning at Dynomite Moto, it dynoed at a stout 52 rwhp — about the same as the factory-claimed crank horsepower of the original engine.
One of the most striking elements is the intake. The 2-1 plenum was fabricated in-house and matched with a DNA filter.
“Thanks to Marios and Dino for their amazing work going into that air filter.”
The wiring and electronics were updated with a lightweight lithium battery and new charging / ignition systems, and a Purpose Built Moto Black Box controls the lighting and switch button functions.
The exhaust is a 2:1:2 system built in-house from 316 stainless, with an X-pipe under the engine and twin PBM torpedo mufflers.
“All polished to perfection before getting a clean and heat cycle to ensure a nice straw gold colour.”
The bodywork is another highlight of the build. The tail piece and bikini fairing were both created in-house, with a custom-mounted PBM 4.5” Headlight and a subtle PBM Delta logo ghosted into the paint.
A set of vertically-stacked Velona Gauges were mounted inside the fairing, and the bars feature PBM switches, custom press-fit bar ends, wrapped leather grips, Domino Classic racer throttle, and Accossato levers.
For the paint, Tom worked with Nathan Bilz at Livin’ Loco, who custom-mixed grays and silvers along with a custom teal blue for the lovely variation on the Yamaha speed block design.
Tom says the riding experience is just right for a well-sorted vintage twin:
“The torquey power delivery right through the rev range means it’s fun anywhere. The thumping of the engine through the 2-1 exhaust is just something you don’t hear on modern bikes…The visceral rattle and vibration from the 1973 Yamaha almost makes you feel like you’re riding in black and white.”
Tom says the bike is one of his personal favorites, and it lit a fire inside him for more classic vintage builds of this caliber:
“I feel like we’ve walked new ground as a custom shop here and I’m really keen to explore this side of things more. Building something almost 50 years old and having it stop people in their tracks when they see it. The painful amount of detail in this build allows anyone with a heartbeat to appreciate the craft…”
In our opinion, “Chrome Dog” blends the timeless appeal of a stainless dive watch with the racy edge of a vintage racer — we love it, and we can’t wait to see what comes from PBM in ’23.