The resto-mod scene is booming in Japan with thousands of ’70s and ’80s superbikes having been transformed into big dollar, bulk horsepower machines while retaining their iconic, classic silhouettes. The likes of AC-Sanctuary, Bull Dock, Bagus and American Dream lead the charge, and they don’t just build the bikes, each shop also has a catalogue of incredible parts and in-house brands, that they’ve developed to produce everything you could possibly need to transform your favourite Japanese retro ride. But after twenty years of friendly rivalry, the arms race has reached a new stage, and firing the first shot, Bull Dock has come out swinging in a big way. Meet their latest creation, a Kawasaki Z1R, in full GTM spec and packing a 1260cc billet engine to take horsepower levels to all new heights.
Most of these shops have been running for well over twenty years, and in the early days, it was without a doubt the original Z1 and early Z900s that proved to be the most popular donor for a full resto-mod conversion. It’s easy to see why, even more than fifty years on it is still one of the most beautiful bikes ever built and has increasingly become a hell of a collector’s item. But as the workshop owners have told us over the last 12 months, finding donors of these classics is becoming nearly impossible, stock has simply dried up, and the value of a good original is too high to contemplate cutting one up. There are also those who prefer the more muscular lines of the later Z1000 machines, and then there is another reason the big capacity bike has become so popular.
The extra hundred cc of capacity can be over-bored even more, with the extra meat on the block allowing builders to safely push to nearly 1200cc. But that has proven the upper limit of these engines, anything over, and compromise and catastrophe are never far away. For Wakui-san of Bull Dock, that was simply not a good enough reason to stop developing these engines, so for this bike, he and his team have come up with one hell of a special package. So, unlike most GTM (Genuine Tuning Machines), this build would be based around the engine and the supporting components, rather than the usual process of working with a client and having colours and specs chosen first.
To start the journey on the hunt for huge horsepower, the engine is disassembled until you have the head, cylinders and lower cases separated into individual pieces. And for this build, only the cases would survive, and even they have been heavily processed, with the bottom customised to accept a modern 6-speed close ratio gearset and also the fitment of a dry clutch with hydraulic actuation. The cylinder head to go on top of the package is a Z1000 J-Spec item, which is CNC ported in-house and finished by hand thanks to the expert staff in the workshop. It’s then rebuilt with a custom set of Kent ST-2 cams, and an entirely new valve assembly before the top covers are finished in Ferrari-style red for contrast.
But it’s the piece that is sandwiched between the cases and that head that makes all the difference, expertly machined from a chunk of billet aluminium. It’s deliberately hidden behind a coat of black engine paint, but the GTM raised lettering lets you know that this is no stock Kawasaki cylinder block. Now having rid themselves of the limitations of the stock unit, custom liners are dropped in and new 78mm high-compression pistons go in. These are a collaboration between manufacturer Pistal Racing, and Bull Dock parts company McCoy, with the crank and forged pistons coming from Vossner and McCoy, and the ultra-light and insanely strong bottom end now displacing a massive 1260cc.
The supporting infrastructure is all of the usual high-end pieces you would expect, Yoshi TMR-MJN 38mm carbs, a full titanium exhaust from McCoy and a massive oil-cooling system, including bypass mod, to help manage the heat of this air-cooled monster. The team are cagey on the power figures, but so big is the torque, that they have had to go for a dry McCoy x TSS slipper clutch, making hard downshifts possible, and clutch maintenance far easier. The hydraulic conversion is all done in-house and up on the clip-on bars, one of the two Brembo RCS radial master cylinders ensures that the clutch feel is still spot on.
Brembo of course also takes care of all the stopping duties, with the front end sporting GP4-RX calipers that clamp down on a set of McCoy x Sunstar 320mm discs, while at the rear a small Sunstar disc is clamped by a twin-piston CNC machined Brembo caliper. On the suspension side of the equation, Bull Dock works hand in hand with Nitron, so the front-end setup is a combination of a McCoy stem and triple clamps, which host a set of Nitron’s conventional design forks in 43mm diameter. Keeping that traditional vibe going, the bike remains twin shock, and so to fit the big tyre and handle the power, a McCoy alloy swingarm is controlled by a pair of Nitron Z series shocks.
The whole chassis of course, like all GTM spec machines, is built to utilise 17-inch wheels and the lightweight forged alloy items are wrapped in Bridgestone RS11s, measuring 120 for the front and a fat as can be 200 section for the rear. It was only at this point, gazing at the stunning mechanical package, that the colour was chosen, and the beautiful grey with black accents was laid over Bull Dock bodywork.
The fuel tank is a lightweight aluminium piece made in-house to match the factory lines, while the front fender and tail section are carbon, with some of the fancy fibre left unpainted. The Z1260 badges leave you in no doubt of this bike’s ferocious punch, and tiny indicators and carbon mirrors get things road-legal. Time will tell if power figures are revealed, but it’s safe to say the number is over 150bhp at the back tyre, and in the air-cooled resto-mod scene, that’s insane.
[ Bull Dock ]