2300cc Zed: Kawasaki Z2300 V12 Motorcycle

2.3L Kawasaki KZ2300 V12 Special from Allen Millyard…  

If you love motorcycles and haven’t been living under a rock for the last quarter century, you likely know the name Allen Millyard. The UK-based shed builder and retired nuclear research engineer has been building mind-blowing specials since 1996, when his first four-cylinder two-stroke Kawasaki triple dropped jaws at the Staffordshire Motor Show.

Since then, the tea-drinking genius has built a host of two-stroke Kawasaki multi-cylinder machines, as well as the world’s smallest V-twin, his 5000cc V-twin “Flying Millyard” special, his Viper V10 bike, and much more.

The Millyard Viper: 8000cc Viper V10 Custom Motorcycle

We experienced our first Millyard specials in person back in 2020, when the annual Barber Vintage Festival was canceled due to the pandemic…except for the races themselves. Fortunately, we were competing in the AHRMA cross-country race that weekend, and the Barber Museum remained open. With no one but racers and staff on site, we had unparalleled access to this hallowed hall of motorcycling heaven. The Barber Museum houses a number of Millyard specials, including his 1976 Kawasaki 850/5 two-stroke, 1974 Kawasaki 1600cc Kawasaki V8, and the maddest of all, Millyard’s 2300cc V12 Kawasaki Zed.

Fast forward a few years, and we decided it was time to do a proper feature on this crazy bit of kit. The donor is a Kawasaki KZ1300 (Z1300 outside North America), the six-cylinder 1286cc water-cooled shaft-drive machine that debuted just a year after the Honda CBX. While the CBX is the better-known six of the era, the KZ1300 boasted 125 horsepower — 15 more ponies than the Honda.

However, the big Zed tipped the scales at 660 pounds with the six-gallon tank topped up, which made it half a second slower in the quarter mile. Cycle World said the KZ1300 ought to be compared to the Honda Gold Wing and XS Eleven…that it was that kind of bike, only better.

“Enormous Bulk and Steamroller Power Combined Into A New Kind of Motorcycle: the Luxury Superbike” –Cycle World, 1979

Enter mild-mannered Millyard, who decided to turn two of these mammoth engines into a V12. The idea came while showing his Kawasaki 1600cc Kawasaki V8 at a classic bike show.

“I was there looking after my V-eight, and there were a couple of KZ1300 crankcases for sale nearby. Some guys saw the cases and said, ‘Suppose you’re going to make a V-12 next, then?'” -Millyard, Motorcyclist

As it turned out, the V12 would be much more difficult to build than the V8. The original cylinders became the front bank of the V, but they’re only five degrees from vertical and Millyard wanted a symmetrical V12 engine. So he set both the front and rear banks of cylinders at 35 degrees, making a 70-degree V12.

The Z1300 engine’s lack of internal symmetry further complicated matters. Unlike the KZ1000, the cams and sprockets are offset.

“I had to cut away all the water passages and oil galleries, then remake them, plus the cam-chain tensioner and new cam runs.”

Then there were the con rods — the most difficult part of the build, says Millyard. He drew up their design on a piece of cardboard — his only drawing for the whole build! Each pair of cylinders has a master rod for the front cylinder and an attached secondary rod for the rear one. Apparently this was a practice taken from old radial aero engines.

Millyard had the rods CNC cut from high-tensile chromoly to be as strong as possible — one of the few CNC components in any of his specials. He also converted the standard-bearing crank to roller bearings so he could pump oil even at low pressure, reducing stress on the engine.

With the standard 62mm cylinder bore and a slightly shorter stroke, the V12 displaces a massive 2281cc. Fuel injection comes from a later KZ1300 Voyager, as does the tubular-steel frame itself, which Millyard cut in half and lengthened. The fuel tank was also cut and lengthened by four inches to reach across the full length of the V12. A hollow section underneath serves as an airbox for the intake system.

The exhaust system consists of four 3-into-1’s welded up out of cheap automotive exhaust tubing, with no silencers because that would be “far too quiet.” Millyard estimates the Z2300’s V12 makes around 250 horsepower. Here’s a clip of the bike idling and revving for your ears:

Other highlights include extra-stiff Hagon rear shocks, a standard fork with additional preload adjusters, and a six-piston Pretech front brake system to haul down the now 770-lb behemoth. Millyard has a full video explaining how he built the bike on his YouTube channel, included below:

Motorcycle author Roland Brown took a test-ride on the KZ2300 back in 2009, and was amazed at how relatively docile and well-behaved the beast was on the road.

“Back in the late 1970s, even those who criticized the original KZ1300’s size had to admit that it handled well. So I wasn’t surprised that even this far more excessive Kawasaki felt stable and comfortable, especially as I took things pretty easy in the bends.” -Roland Brown, Motorcyclist

The Barber Museum themselves have also made a great video detailing various features of the Z2300, which remains in their collection.

Allen Millyard is a gift for those of us who love motorcycles. A man who dreams up some of the most mind-melting creations on the planet and has the vision, skills, and grit to pull them off. If you’re ever in the vicinity of Birmingham, Alabama, don’t miss the Barber Museum to see some of his handiwork in the metal. You won’t regret it.

Follow the Builder

Instagram: @allenmillyard
YouTube: @AllenMillyard

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