Typhoon Shanshan has made landfall in Japan and has tragically claimed several lives, and as it approached the country 24 hours ago, most people were evacuating or bunkering down. However, not Hiroyuki Nakamura, the boss of the world-famous AC Sanctuary. Nakamura-san is a man who insists on perfection, and his service to his customers is legendary. Knowing the storm would prevent him from having this freshly completed Kawasaki Z1-R resto-mod delivered to its owner, he did the next best thing he could: ensuring that the client could at least feast on some photos of the finished bike. RCM-634 sports a menacing sky-grey look, a thunderous sound, performance to die for, and it’s been built to last a lifetime.
To the untrained eye, almost every bike from the mega AC Sanctuary factory appears to be pretty much the same. You see it in the comments: “Seen one, seen them all.” But that couldn’t be further from the truth. A huge part of the difference lies in all the places you can’t see. This machine fits into what Nakamura-san calls the RCM Life Package specification, which means it gets all the stunning looks of all AC builds, but the mechanicals are set up to be ridiculously reliable. There is also an emphasis on extra comfort, tailoring the bike to suit the client’s physical dimensions and making it something you can ride all day, every day.
But just because this RCM isn’t built for wild laps of the Tsukuba Circuit doesn’t mean it doesn’t pack a punch. For its transformation, the bike is broken down, the engine is sent off to one part of the facility, and the chassis is placed on the jig. To ensure a lifetime of fun riding, the engine isn’t one of the company’s big-bore power producers. Instead, the bottom end is treated to laser-guided honing and a set of 1mm-over forged pistons. Those pistons come from AC’s in-house machine shop, DiNx, which also takes care of the crankshaft. It is treated to a rebuilding and balancing job that is key to the bike’s reliability, performed on high-end machinery, and a process that “is revolutionary, so, unfortunately, it is a trade secret,” Nakamura-san smiles.
The rest of the engine doesn’t miss out either, with a full CNC port and polish of the head, new valve guides, and a three-angle valve job. To ensure excellent thermal management, internal modifications are matched up with one of the company’s Nitro Racing oil-coolers, this one of the curved variety, which allows it to be mounted further away from the exhaust. And oh, what an exhaust it is! The full titanium system is the sort of work of art you’d expect to see in the MotoGP paddock. With the material not conducive to mandrel bending, it’s precision laser-cut and welded. Fueling is a little more conservative than some AC builds, but the throttle response is spot on with the Yoshi carbs.
In the chassis shop, the bare frame is aligned to within an inch of its life and then treated to the famed AC Sanctuary 17-inch wheel modifications. The stock machine came out of the factory on 18s, with other sports bikes at the time running diameters up to 19 inches at the front. But decades of R&D from all the major manufacturers, race teams, the famed Eddie Lawson wheel size testing, and tyre development have proven that 17 inches is just the right amount. While you could just bolt on that sized wheel, Nakamura-san has spent a lifetime developing the chassis changes needed to get the geometry of a classic sports bike to work with modern rims and rubber.
The wheels are from Oz Racing, originally intended for a later model Kawasaki, the ZRX, and are specified in widths of 3.5 and 5.5 inches front to rear. The front forks are Ohlins EXM, in a traditional configuration, and are held in place by AC’s own Sculpture triple clamp and steering stem kit. Black was the client’s choice, and he also asked for a fully welded and braced Sculpture swingarm in black. The braking is all beautiful stuff with Brembo GP4s up front, AC-spec Sunstar discs all around, and the feel at both levers is spot on, with radial masters and a hydraulic clutch conversion.
But again, not all bikes from the company are the same, and to suit the client and create an all-new product, the handlebars are a one-off creation. The idea came when meeting the challenge of having the rider comfortable while also clearing the bikini fairing. Nothing on their shelves would fit, so a piece of 22mm steel was put into the bender and a new set of low bars formed. On the inside, they have been partially filled, balanced, and then threaded before bar-end weights were fitted, all to reduce the amount of vibration transferred to the rider’s hands. The seat too is not a ‘70s piece but is made to appear that way and built up with the latest foam and gel for the ultimate in comfort.
The bodywork is, of course, flawless. From the masculine lines of the fuel tank to the picture-perfect paint, this is custom bike building at its best. The tinted screen was part of the client’s request for that blacked-out look, and the carbon mirrors add to the sleek profile. Below them sits another one-off creation for this bike: the dash, which all starts with a single sheet of carbon fibre. In goes a mix of original idiot lights and the glorious Stack gauges, and because this machine can be ridden every single day, a fuel gauge has been neatly plumbed in. We’re all hoping the worst of the typhoon has passed, and when the coast clears, one lucky man will take possession of the Z1-R of his dreams.
[ AC Sanctuary ]