Thundering Super-Sport: Honda CB900F Restomod

Honda CB900F Restmod

RCM-604 by AC Sanctuary… 

When the Honda CB900F first appeared in 1979, it wasn’t available in the States, as Honda was worried it might steal the thunder of the mighty CBX. American riders grew green with envy at images of European riders hustling the 901cc superbike through the winding roads of the Alps and Pyrenees.

Honda CB900F Restmod

The six-cylinder CBX might have boasted a higher top speed, but on a track or canyon road, the CB900F would be the clear winner.

“A thundering Super-Sports bike with devastating performance and an unwavering stamina.” -Honda

Honda CB900F Restmod

The CB900F was a direct descendant of the CB750F, featuring exotic technology for the era: four cylinders, dual overhead cams operating four valves per cylinder, and the cams linked to the crank by two silent-type cam chains. Max output was 95 horsepower at 9000 rpm — just 10 ponies down from the heavier CBX.

Honda CB900F Restmod

The CB900F would run the quarter-mile in the elevens, and by the time it reached US shores in 1981, top speed was clocked at 130+ mph. In 1982, Fast Freddie Spencer and team trounced the competition for a podium sweep in the Bell Superbike 100 at Dayona.

Honda CB900F Restmod

But the advent of liquid-cooled, aluminum-framed sport bikes was nigh, making the CB900F the height of a certain breed.

“The ultimate statement of the old air-cooled technology Honda had done so much to create.” -Kevin Cameron

Honda CB900F Restmod

Enter Hiroyuki Nakamura and his team from Japan’s AC Sanctuary, builders of the baddest Japanese restomods on the planet. While Nakamura-san is best known for his Kawasaki Zed and Ninja builds, he’s also brought his particular set of skills to the Suzuki Katana and Honda CB-F series, such as the CB1100F we featured a couple of years ago.

Resto-Monster: Honda CB1100F Restomod

With these RCM (Radical Custom Manufacture) builds, every facet of the original machine’s performance is upgraded: power, suspension, brakes, wheels, rubber, etc.

“As old bikes, customization and tuning can improve their dynamic performance, and the obvious difference in performance changes is a big attraction.” -Nakamura

For one of his latest and most time-consuming builds — RCM-604 — the owner chose the mid-displacement CB900F from the CB-F series. The chassis was stretched, straightened, reinforced, and repainted, while the wheels were switched to OZ Racing 17-inchers to accommodate modern rubber — Pirelli Diablo Rosso IV tires, to be exact.

The bike is now running 43mm Öhlins forks with Brembo dual-disc brakes and more Öhlins suspension in the rear. The rear swingarm is a billet Sculpture piece, an RCM exclusive produced in-house. While exotic, such trappings are to be expected for any RCM build.

But problems began to arise when it came time to overhaul the engine.

“The manufacturer’s stock is decreasing year by year, and the situation is getting tougher. Even though engine overhauls require internal combustion engine processing, it is difficult to replace consumable parts. In order to improve the completeness of the overhaul, it can be said that procuring new parts is the biggest challenge.” -Nakamura

Honda CB900F Restmod

In order to make the owner’s dream come true, Nakamura-san’s team spent hours “staring at auctions and overseas parts sites,” trying to find the consumable parts necessary to carry out the rebuild.

Honda CB900F Restmod

He says the issue is the same for any CB-F, CB1100R, or CBX1000, but ultimately it depends on the owner’s strong desire to make it happen.

“This is because without passion, it would not have been possible to make it, with a long production period of a year or with a sense of cost for parts that are difficult to obtain. The owner of this RCM-604 had exactly that kind of feeling, which is why he was able to make it happen. RCM for the CB900-F, which is obviously more difficult to obtain parts for than the air-cooled Z series or Ninja series. It has been reborn with modern specs and is still able to run well today.”

Full Gallery

 

Chassis (17 inches)

Frame Original frame reinforcement
Wide laydown processing Powder coating after blasting
Steering stem SCULPTURE SPΦ43 fork TYPE-1 Z1 processing reuse
Handlebar Daytona RCM Concept Handlebar
Front Fork OHLINS Upright Φ43 E×M Package
Front Wheel OZ Racing GSAA RS-A for ZRX1200 3.50-17
Front Brake Brembo P4 30/34 Cast Axial Caliper
(Master) NISSIN Brake Master Φ5/8
(Brake Hose) Allegri Short System
(Disc) RCM Concept Φ320
(Support) SMB Axial-Mount Caliper Support
Front fender NITRO RACING Ceiling fender kit (TYPE naked, FRP)
Swing arm SCULPTURE R.C.M exclusive wide swing arm polished finish
Rear shock OHLINS Legend Twin
Rear wheel OZ Racing GASS RS-A for ZRX1200 5.50-17
Rear brake Brembo Cast Rear Caliper P2 34
(Master) NISSIN Master φ1/2
(Brake hose) Allegri Short System
(Disc) Sunstar Φ250
(Torque rod) SMB Rigid mount
Tire (Front) Pirelli Diablo Rosso IV 120/70-17
(Rear) Pirelli Diablo Rosso IV 180/55-17
Drive chain EK530RCM
Sprocket (Front) 530-18 teeth
(Rear) Sunstar 530-42 teeth
Chain line 10mm offset

Body

Back step NITRO RACING
Pandem step NITRO RACING
Seat Sponge shaping, leather reupholstery
Drive sprocket cover Jaze
Paint Okushin

Intake, exhaust, cooling, electrical system

EX muffler NITRO RACING Weldcraft 3D
Silencer NITRO RACING Conical Titanium VⅢ Half polish
Carburetor Mikuni TMR MJN Dual Stack Ф36
Fuel Cock PINGEL
Ignition System AS Uotani SP2
Cooling System NITRO RACING×EARLS OIL Cooler 9 inch 13 stages
Bore/Stroke 65mm/69mm
Displacement 915cc
Piston manufacturer DiNx
Cylinder DiNx boring & honing top surface minimum value grinding
Clutch Clutch housing disassembly damper replacement
Valve guide Valve guide replacement
Valve seat DiNx seat cutting processing
Cylinder head DiNx Bottom surface minimum value surface grinding
Cam chain J’s
Cylinder stud Metal Gear Works

Follow the Builder

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

More AC Sanctuary Restomods…


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2 Comments

  1. I am pretty sure these guys could not build an ugly bike, even if they wanted to. We often see builders put a lot of expensive parts on a bike and call it done, but AC does it so well thought out and the product is always just beautiful. Now if I could get them to do my Honda CX650 turbo!

  2. A great bike, with some excellent modifications, a good street sleeper as well.

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