There’s a well-worn path, or more accurately a shipping lane, that has been bringing customised cars from Japan to Australia for decades. The JDM scene has had its highs and lows, but its impact on automotive culture in the land down under is impossible to deny. What hasn’t been flowing as freely, however, are custom motorcycles, or even JDM motorcycles in general. A few have rolled in, but for the most part, Australian dealers and builders have been able to keep the two-wheeled community satisfied. But the internet just opens up more and more options, and the language barriers are taken care of by technology too. So, with a simple chain of emails, one very wise and lucky Aussie ordered himself RCM-649. A Kawasaki Z1000 Mk2, which is an unbelievable world-class custom creation from the kings of the resto-mod, AC-Sanctuary.
“We constantly receive inquiries about RCMs from overseas, and over the past 20 years, dozens of RCM units have been exported, mainly to Europe, America, and Taiwan,” explains AC boss Hiroyuki Nakamura. And then in 2024, Australian John Lewis decided he had to get in on the action and sent an email to Nakamura-san. They exchanged ideas about the sort of build John was looking for, the specifications he was after and then had to sort out a donor bike. “We were considering sending the base bike from Australia to Japan for production, but after consulting with Mr John Lewis, we decided to prepare it in Japan.”
Purchase prices, shipping costs, registration requirements and a host of other issues mean this is not an easy decision, but ultimately the donor was found in Japan and the AC team could immediately get to work. Stripping the bike is important, but given so few stock parts will ever go back on, it doesn’t take long before there is a bare frame sitting on the floor. And one of the first tasks is the creation of the special key tag that goes with each bike, and the ID plate from AC-Sanctuary that’s attached to the neck, as they are now the official manufacturer for legal purposes moving forward. Then the meticulous work of building an RCM bike can commence, with the chassis stuck in a jig to be aligned.
The frame is then heavily gusseted around the neck, the steering lock is moved higher and a host of strengthening modifications are carried out. Next, all of the brackets and tabs are cut off, and even the shock mounts are removed from the frame. This allows the chassis to go into another jig, this time a lay-down type, where the new mounts and swingarm bracing can be completed. “Precision is crucial for the laydown processing of the rear suspension, including the mount positions and angles on both sides.” Drilling, welding and grinding all take place with the chassis locked tight into the jig, allowing for results that are incredibly accurate, surpassing OEM standards and entering the world of pure perfection.
And if we’re talking about perfect, then Nakamura-san will simply accept no other alternative in the preparation of an engine. The stock motor is pulled down and the top and bottom halves are separated. The bottom goes to the engine building room, where a new six-speed closed-case gearbox is adapted to fit, the block is cross-drilled to help control internal pumping pressures and the hydraulic clutch and covers are fitted. The lower rotating assembly is prepared in the DiNx part of the facility, with a fully balanced crank, custom machined forged pistons in an oversized spec, and hand-selected rods are all slotted into place.
The top end is given the full DiNx treatment too, and it starts with a total stripping of the cylinder head, which is then loaded into the first CNC machine, to add new holes to allow for the twin plug conversion. Nakamura-san believes this is vital on all Z motors for making big, reliable horsepower and then the head is both hand and machined ported and polished. The cams are from Yoshimura and the adjustable sprockets come from the US, but the rest of the valve train is all made in-house. This includes larger valves with reduced diameter stems, custom coated tappets with pressure reliefs, and every last part is weight-matched for smooth operation.
Only then can the engine be assembled and items like the full bank of Yoshi carbs go on and be joined by that beautiful full titanium exhaust system. The tuneable ignition system comes from the folks at AS Otani, but with extra coils for the twin plug setup, hidden brackets help to keep the look ‘stock’. The bottom of the engine is custom, with a fully machined oil pan, featuring a trochoid-type oil pump, bolted up to ensure there is no starvation, no matter the speed or the G forces achieved. This is the level that AC goes to in their pursuit of perfection. Even their own Sculpture swingarm was cut up, and braced before being refinished in black to suit this particular build.
Then goes on all the best gear as used by WSBK teams, Ohlins suspension front and rear with a Sanctuary triple clamp set. The braking is by Brembo and Sunstar and the ultra-lightweight wheels come from the fine folks at Oz Racing. A 190-section rear tyre was requested, and along with the 17-inch wheel conversion, this is all taken into account from the start; including the frame processing, to the use of a longer output shaft and all of the sprocket and chain choices. The paint and panel work is absolutely flawless and the functionality means that this racer is more than ready for the road. But John will have to wait a little longer, the bike needs a shake-down test and then will be displayed at the Tokyo Motorcycle Show before it finally picks up its passport and heads home, Australia is calling.
[ AC Sanctuary ]