The fundamental styling of one of the world’s most beautiful classic motorcycles which is then combined with an excellent modern drive-train and you should have a fan favourite amongst the custom crowd. But while many of the factory retro remakes have been a huge success, the Kawasaki Z900RS has struggled to take off. Pipeburn tested the cafe racer styled Kwaka when it was launched five years ago and found it to be a brilliant machine – if not a little expensive. Now, however, the Japanese scene has warmed in a big way to the all-new Z and you knew that would only mean one thing. Chiba Prefecture’s AC-Sanctuary led by master Nakamura-san would set out to build the best one yet, and they haven’t let team-Z down with RCM-534.

For those who haven’t been paying attention, the AC-Sanctuary RCM line started in 2000 and after 20 years, the RCM serial number exceeded 560 bikes. In 2021, starting from serial number RCM-572 the old meaning of Real Complete Machine has been changed to Radical Construction Manufacture. Whichever name you use, the RCM line of bikes are all one-off builds that leave absolutely no stone left unturned in their pursuit of perfection. So, with this being the first Z900RS for the company, the bike took longer than expected as the team sought to develop a range of parts for the Kawasaki to be sold under their in-house brands.

“Around 2020, we belatedly started to build a Z900RS RCM at Sanctuary. I wanted to make more, but I was busy with the usual RCM production, and it took a long time of more than two years to finally complete it,” Nakamura-san explains about the beautiful bike before you. But what he wanted to ensure was that the AC Z was different to most of the others being built, which mainly focused purely on cosmetic changes. There is nothing bolt-on however about any RCM build and with a new Z in their possession, the AC team had the bike stripped down and the chassis in a jig. The steel trellis frame is a decent bit of kit, but to give it the rigidity it needs for RCM levels of performance it would have to be improved.

Given that the bike has no lower cradle, this was the most obvious area to improve, and CNC bent 25mm rails were manufactured to suit, with machined gussets and connection points helping them merge as one with the main frame. For this build, it has been left in a polished look to show off the part, but it is envisaged that most customers will select to have theirs in a frame matching black. The down tube kit also helps to add strength to the swingarm pivot point and you know that Nakamura-san was going to create something brilliant here too.

Offered under the Sculpture branding, the wide swingarm kit not only allows the Z to run a bigger rear tyre, but the CAD designed aluminium piece uses the company’s extensive racing R&D to drastically improve the mechanical grip of the bike and the subsequent feedback to the rider. Now paired up with a 350mm fully adjustable shock from Ohlins, the impressive factory handling is now in another league. To ensure the front gave the same level of confidence, the team designed an all-new billet aluminium steering stem and triple tree combo to change the geometry and is matched to a pair of Ohlins FGRT207 forks, and even the front fender is supplied as part of the kit.

To get things rolling there is only one choice for Nakamura-san, “Of course, for the front and rear wheels, the highest quality wheel ‘OZ Racing’ is used, which is currently the number one road race world championship item.” That racing-inspired design is extended to the braking and AC-Sanctuary partners with the best in the world to piece together a package that includes calipers and master cylinder by Brembo, and big drilled discs from Sunstar. The bracket for the rear caliper is an in-house piece and the levers are from the RCM range, a nice addition to your own Z if you can’t afford a full RCM build.

The 948cc engine, based on the architecture of the ZX-9, is a proven old performer from Kawasaki that has been given a very modern makeover. Nakamura-san didn’t feel the need to go overboard, although, for those who wish to track the bike there is the option of selecting a bank of Mikuni carbs. The exhaust system is of course a full Nitro Racing 4-into-1 titanium setup that spits out of the V3 muffler. One flaw the team found was in thermal management, hence the huge aluminium radiator they’ve developed, with a smaller ’round’ version now offered for those who don’t want the full race bike look.

To give the visuals a real RCM feel, the bodywork has been treated to a simply stunning original Z inspired paint job. Then to enhance the clean look and add more parts for the public, the bike benefits from the newly developed fender eliminator kit, inner carbon rear guard and some gorgeous billet machined mounts for the factory headlight; any of which will give a Z owner some beautiful bling for their bike. The final modifications come in the form of the controls, with the machined risers and RCM bars, matched up to a set of fully adjustable billet rearsets.

So, now whether you want a few parts or a complete custom machine, AC-Sanctuary has ensured the Z900RS has finally been taken to the all-conquering heights that it always deserved.

 [ AC Sanctuary ]