Six-Cylinder Salute: AC Sanctuary CBX1000 Restomod

AC Sanctuary’s RCM-693 CBX, straight from the Tokyo Motorcycle Show…  

Today, we’re thrilled to present the new Honda CBX1000 from Japanese master Hiroyuki Nakamura of AC Sanctuary. Just last year, we featured RCM-688, the first-ever CBX to receive the full RCM (Radical Custom Manufacture) treatment for which these Nakamura-san and his “restogods” are known. 

Radical Six: Honda CBX1000 Restomod

That bike, however, was the later model, which Honda had turned into more of a sports tourer with a big front fairing, de-tuned engine, air-adjustable front forks, Pro-Link monoshock rear suspension, optional panniers, etc. We’ve always preferred the original naked twin-shock model, which Honda originally developed as a superbike.

Honda had produced the legendary six-cylinder RC series of Grand Prix racers in the 1960s, but the CBX’s advanced DOHC 24-valve inline six-cylinder engine was a first for a Honda street bike. At full song, the 105-bhp six howls like a Formula One — one of the most glorious sounds in motorcycling history. 

Below, Nakamura-san gives us the full skinny on this big and brutal six. At the bottom, you’ll find a video of the build process as well. Enjoy!

In the Builder’s Words…

(Translated from the original Japanese…)

Under the guidance of the Sanctuary staff, I was given complete creative freedom to build this as I saw fit. To be precise, it’s a CBX1000 that took much deliberation and discussion about “this way or that way” — saying “do whatever you want” might sound like fun, but that’s not always the case. 

Our first CBX was the RCM-688, which was ordered from Taiwan, but that 688 was a later model, so this early model is essentially our first attempt… My basic experience with the later model 688 was helpful, but I struggled with the unique characteristics of the earlier model, and it was only after much trial and error that I finally managed to complete it.

The subframe modification, which involved slightly changing the rear suspension angle in preparation for the 17-inch wheel conversion, was made possible by adapting the “Z-specific laydown jig” currently sold commercially by Noblest as a special tool, resulting in a very precise finish on both sides.

Because the original suspension mounting bolts were no longer used due to the subframe modification, an additional mounting boss was welded on beforehand, and a one-off, handmade V-shaped silencer hanger was created by bending an aluminum pipe in a 3D shape. These are details that I had planned and envisioned in my mind from the very beginning.

The new SCULPTURE swingarm, a monoblock design with a one-piece bracket into which a ribbed square pipe acting as a stabilizer is inserted, features a rear suspension mount that allows for adjustment of the lower part of the rear suspension within a rotation range of 50 degrees.

As you may already know, the wheels are the new 8-spoke aluminum “GP-8R” from Italian manufacturer OZ Racing,
which will be released worldwide this spring.The disc rotor is the top-of-the-line “OMEGA” disc from SUNSTAR, which will be released this summer. As an RCM concept specification, it features a special 10-connection configuration instead of the usual 8-connection.

We’ve just received some hot paddock photos, so let me interrupt and share them with you. TOT’s practice run has begun. T. Ukawa and the CB1100R racer. Wow, that’s great! Mr. Ukawa, I’m rooting for you in your exciting battle in the air-cooled strongest and fastest class at the tournament in May! Oh no, I’m getting carried away! Let’s get back to the main topic.

The footpegs were officially added to NITRO Racing’s lineup this spring for the CBX1000 . Furthermore, this 6-2-1 Weldcraft 3D titanium exhaust is also being released as part of NITRO’s official product lineup. This information is not reflected on our website, so please contact Noblest directly for details.

As for the engine, this is the twin-cam 24-valve air-cooled six-cylinder that is synonymous with the CBX1000. Of course, we didn’t just paint the base car’s engine black with Cerakote. As the saying goes, “Engine overhaul is all about precision internal combustion engine machining,” and DINKS has put its full menu of services into practice. DINKS, Noblest’s precision internal combustion engine machining division, is truly a reliable partner.

The process begins with the dynamic balancing of the journal-lapped crankshaft, followed by rough boring of the cylinders, and then precision honing using a Rottler H85A CNC automatic vertical honing machine to achieve the correct cylinder angles and piston clearances. The cylinder heads are also fitted with oversized valve guides, then seat-cut, and finally all deck surfaces are ground using a general-purpose CNC machine, the YZ-500WR.

If you neglect the internal combustion engine machining even a little, no matter how excellent the parts you use to assemble the engine, it will never run perfectly, so this is a situation where you can’t skimp.

I’m well aware that this isn’t a machine designed for sporty riding on a circuit, but since it’s an RCM, I’ve positioned the exhaust manifold as close to the engine as possible to maximize the lean angle. The muffler end is fitted with Nitro’s new Swallow Titanium Silencer in black, which will also be released this spring. Even from a side view, you can sense that it has well-proportioned dimensions.

The seat is an original design, with the base cut, bent, and welded from sheet metal. Can you tell that the silhouette is just a little bit different from the normal version?

“True craftsmanship lies in the details.”

This phrase is the slogan, motto, and core principle behind RCM’s production. Many of you may have seen this RCM-693 at the Sphere Light booth at the Tokyo Motorcycle Show. I had planned to announce the sale on my website after the exhibition ended, but…this RCM-693 sold very quickly.

The person who fell in love with it at first sight and purchased it was Mr. T, the owner of the RCM-248 air-cooled GPz1100, and also an international rider! I heard that Mr. T is thinking of using this CBX to become a circuit riding instructor…

Follow the Builder

Website: www.ac-sanctuary.co.jp
Facebook: www.facebook.com/ac.sanctuary

More AC Sanctuary Restomods…

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