RCM-554: 1165cc Zed from AC Sanctuary…
The Kawasaki KZ900 was the direct successor of the mighty Z1. At the time of its introduction in 1972, the original 903cc Zed was the largest, most powerful four-cylinder Japanese motorcycle ever made — a true alpha bike:
“With brutish, swooping lines and quad pipes clutching a magnificent engine like a black heart in an iron fist, the Z1 was an archetype of menacing style. Natty in its distinctive candy color scheme, the big Kawasaki looked like a heavyweight boxer out for a night on the town…” –Ultimate Motorcycling
Introduced in 1976, the KZ900 was essentially an updated Z1, featuring smaller 26mm Mikuni carbs, thicker-walled frame tubing, a locking gas tank, and different side covers and taillight design. Despite these refinements, the KZ900 was still a beast:
“Tuning alterations and smaller carbs shaved a few watts off the powerplant in an effort to refine the bike’s raw grunt, but riding a KZ900 today precipitates a case of adult-onset Deja Vroom.” –Ultimate Motorcycling
If you’ve been following BikeBound for very long, you know we’re big fans of Japan’s AC Sanctuary and their RCM (Radical Custom Manufacture) series — a lineage that contains some of the baddest air-cooled Japanese restomods on the planet.
Though most of RCM’s orders used to come from Japan, the AC Sanctuary name is now known and respected all over the world. Founder Hiroyuki Nakamura says they now receive 1-2 orders every year from overseas.
This one came from a German engineer and client who sent over the KZ900 frame, which received RCM’s “Stage II” frame reinforcement and processing.
Meanwhile, the engine was rebuilt with a high-compression 1165cc Wossner piston kit, Yoshimura ST-2 cams, oversized valves, ported and polished dual-spark heads, and a 13-stage oil cooler with high-pressure pump.
Like most all RCM builds, this “KZ1165” is rolling on Öhlins suspension, OZ Racing wheels, and Brembo brakes. Says Nakamura-san:
“As you know, these three manufacturers’ products are truly the world’s highest quality brands, and they are the only top category products suitable for RCM. It’s a solid undercarriage.”
Since the frame came from Germany, the AC Sanctuary team couldn’t legally ride the finished bike on Japanese roads, so they rented a short circuit for testing purposes — talk about dedication!
Below, we hear the full story on the build.
RC-554: In the Builder’s Words…
It is not rare now to receive an RCM order from overseas. Every year, about 1 to 2 orders. It’s the current situation that RCM builds are always being produced on the premise of export. The serial number rules remain the same. Like Japanese users, there’s a unique serial number that does not have an equal anywhere. A key holder bearing the serial number is handed over, and no matter how far away the bikes goes, it’s a genuine RCM.
This RCM-554 is built on a frame sent from a German owner. The base chassis is the KZ900, which is more evolved than the Z1. The KZ900 was selected based mainly on the frame. It’s still an air-cooled Z, with an attitude that pursues performance, which is in accordance with the concept of RCM.
The engine reflects this attitude. We began with a rebuild of the crankshaft and the TW company’s 6-speed cross transmission. From the owner’s home country of Germany come the Wossner pistons, a high compression package — a big bore with twin spark plugs. The engine has a sharp focus on tuning, with Yoshimura ST-2 camshaft, big valves, and port polishing.
Of course, adding this much will affect the life of the engine, so it is essential to equip it with an oil cooler, and a trochoid rotor-type high-pressure oil pump is an indispensable item to enhance the oil cooler function. Partly because the owner himself is an engineer, this part choice was decided without hesitation.
The frame that receives the power-up engine is Sanctuary’s original frame reinforcement STAGE-II. High-precision manufacturing using various special jigs such as rear suspension laydown and in-line processing to secure the drive chain track. It is an intricate frame.
The undercarriage fitted to such a frame is a masterpiece from the world’s top manufacturers: a combination of Brembo brakes, OZ Racing wheels and Öhlins suspension. As you know, these three manufacturers’ products are truly the world’s highest quality brands, and they are the only top category products suitable for RCM. It’s a solid undercarriage.
Since there is no way to change the performance of individual parts, it’s always the best at RCM. It can be said that this is a common feeling not only in Japan but also in the world.
Because RCM-554 is based on the frame sent from Germany, it cannot be registered in Japan, and a road test on public roads is not possible. For that reason, we are renting a short course and doing a road test before exporting.
As for the language barrier when ordering from overseas: Although there are some difficulties, we would like to show our willingness to respond as long as there are requests from overseas such as “I want RCM!”
Chassis (17 inch wheels)
|Pillion pegs||NITRO RACING TYPE-2|
|Seat||DAYTONA RCM CONCEPT COZY SEAT|
|Clutch Master||Brembo RCS radial clutch master|
|Drive Sprocket Cover||NITRO RACING NEW clutch plate black/black|
|Clutch hose||Allegri Short System|
Air intake/exhaust/cooling/electrical system
|Exhaust||NITRO RACING Titanium Hand Bent Full Exhaust Heat Polish|
|Silencer||Grenade Titanium VIII Heat Polish|
|Carburetor||MIKUNI YOSHIMURA TMR MJN 38Ф CARBURETOR DSF|
|Ignition system||AS Uotani SP2 Twin Plug Package|
|Cooling system||NITRO RACING 11 inch 13-speed flat oil cooler|
|Piston Maker||WOSSNER Piston 75Φ Piston Ring WPC Treatment|
|Crank||Bearing replacement full rebuild|
|Cylinder||Pam’s EST Liner Boring & Palfos M treatment after honing top and bottom surfaces are ground to a minimum value|
|Transmission||6-speed cross transmission Chainline EVO system / Dock clearance precision shim adjustment|
|Crankcase||Top surface minimum surface grinding|
|Intake Valve||Pam’s Big Valve Φ37|
|Exhaust Valve||Pam’s Big Valve Φ31|
|Valve Guide||Oversize valve guide replacement|
|Valve Seat||Oversize valve seat ring Seat cut processing|
|Cylinder Head||IN & EX Port Machining, Polishing, Twin Plug Machining, Lower Surface Minimum Value Surface Grinding|
|Cam Chain||EK cam chain|
|Timing Parts||Yoshimura lightweight adjustable cam sprocket|
|Cylinder Stud||SMB Chromoly Cylinder Stud Bolt|
|Cylinder Head Nut||SMB Chrome Molybdenum Nut|
|Other||Yoshimura valve spring / Yoshimura valve seat / Yoshimura lightweight retainer / SMB high pressure oil pump KIT|
Follow AC Sanctuary