Wild File: Homebuilt Kawasaki 2300cc V-12 Motorcycle

Allen Millyard's first attempt at a burnout doesn't work. In what we hope was an isolated incident of "mad scientist gone tame," Millyard fails to feed the rear tire enough good ol' V-12 torque. Rather than engulf the scene in smoke and sweet music, the big Kawasaki simply inches forward with its front tire squeaking in protest. But Millyard's not going to be beaten, and tries again—and this time the rear Michelin breaks traction. Suddenly, Millyard has a massive grin on his face, and is revving the hell out of his latest creation, which makes a glorious growl through its open pipes while smoke pours from the spinning rear tire.

The 41-year-old nuclear research engineer from Berkshire, west of London, has good reason to be pleased with his unique, hand-built machine. At first glance it looks almost like a standard version of the gigantic KZ1300 six that Kawasaki released in 1978/1979 in the rush toward ever larger and more powerful superbikes. But this particular machine is considerably bigger; it includes two complete KZ1300 cylinder blocks grafted together to make a 70-degree V-12.

If you know anything about Millyard and his history of building bikes—especially old-style Kawasakis—with more than their original number of cylinders, the V-12 Kawasaki won't come as a complete surprise. After starting this wacky process by creating Honda V-twins using a pair of C90 and then SS50 cylinders, he produced a string of Kawasaki two-strokes with four-, five- and even six-pot powerplants based on the old air-cooled triples. Then he built an even more ambitious special, a 1600cc V-eight compiled from two four-cylinder KZ1000 engines (which we profiled in September '02).

It was while at a classic bike show with that V-eight that Millyard hatched a plan to go a stage further with a KZ1300-based V-12. It wasn't even Millyard's idea. "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?' I said no, I wasn't, and they replied that it would be impossible anyway. Of course, as soon as they said that, I had to build one. I spent the next two days thinking about how I was going to do it, and by the time the show ended I'd worked it out."

Designing and building the V-12 required plenty of thought even for Millyard because this project was far more ambitious than the V-eight. The creation of the engine was similar in that he once again retained the original cylinders as the front bank and grafted on a second set at the rear using a shared crankshaft. "The original cylinders are only five degrees from vertical," Millyard says, "but I wanted to make this engine symmetrical, so I set both banks at 35 degrees from vertical to give a 70-degree V-12."

Creating the V-12 was made much more difficult by the six-cylinder engine's lack of internal symmetry. "The rear head is cut and reversed, and runs backward, but this caused a nightmare because the KZ1300 cams and sprockets aren't in the middle of the engine, as they are on the KZ1000," Millyard recalls. "The stud positions are slightly different and the cams are offset. So I had to cut away all the water passages and oil galleries, then remake them, plus the cam-chain tensioner and new cam runs. I made a cam chain from two heavy-duty Hyvo chains welded together. It's about six feet long—taller than me!"

The only thing smaller than standard is the engine's stroke, which is reduced from 71mm to 63mm using flywheel weights from Kawasaki's 750cc H2 triple. "I wanted to reduce a bit of stress in the engine and also have a roller-bearing crankshaft," he says. "The KZ1300 had some problems with its plain bearing crank and I didn't want to make it worse, so I converted it all to roller bearings so I can pump oil through even at low pressure."

Retaining the original 62mm bore gives a capacity of 2281cc. Pistons, valves and camshafts are standard, though cam timing has to be slightly out because the cams aren't quite symmetrical, and don't run backward perfectly. "I've probably lost a few horsepower, but that doesn't matter. The standard KZ1300 made 130 hp, so this engine has the potential to make 260!"

A more serious problem was that the liquid-cooled six, though huge, has a more modern and compact crankshaft design than the KZ four, so Millyard could not repeat his V-eight trick of using pairs of side-by-side con-rods. Instead he designed new rods based on radial aircraft engine practice, with the front one of each pair of cylinders using a master rod, to which is attached a smaller secondary rod for the rear cylinder.

"That was the only drawing I did on the whole bike, using cardboard templates," Millyard recalls. "The con-rods were the hardest part of the engine. Everything's so narrow and there's very little bearing area, so I had to use the strongest material I could." Finding the required grade of high-tensile chrome-moly steel proved difficult. "I had to buy five-inch-diameter round bars, then machine a 20mm thick plate out of the center, so 90 percent was wasted. I couldn't cut it with a saw, and it would have taken months on my old milling machine. But luckily my friend Chris Halliday of Pretech (who supplied the bike's brakes) offered to do the rods on his CNC machine."

Fuel injection is from a late-model KZ1300 Voyager, and is improbably close to standard, though Millyard added some volume switches from a radio, which allow the system to be fine-tuned. He built the exhaust system himself using various cheap pieces of a car exhaust. "It's a straight-through system, basically four 3-into-1s linked up. It's designed so I can fit standard silencers, but I don't want to because it'd be far too quiet."

Plenty of other standard Kawasaki bits have found their way onto the beast. The starter motor, alternator and regulator are all late-model KZ13 items. The radiator was made by taking two standard aluminum units, cutting the top off one and the bottom off the other and welding them together. The system is plumbed with a large-bore central heating pipe, and uses a rally car electric pump to keep coolant circulating whenever the ignition is switched on.

The chassis looks almost normal until you realize that even the KZ1300's notoriously huge fuel tank could not possibly extend above such a monstrous motor. Millyard cut the original in two and added a four-inch-wide strip to enlarge it, taking the opportunity to hollow out extra space underneath as an airbox for the filterless intake system. Capacity is still a generous eight gallons, which is just as well because consumption was initially around 8 mpg....

The tubular-steel frame is from the Voyager version of the KZ13, once again cut in two and enlarged, this time with four extra pieces of tubing, plus some bracing where it can't be seen. The necessarily huge 30Ah battery takes up all the space beneath the seat, so other parts had to be relocated with the aid of a homemade wiring loom.

Millyard was helped by a classic Kawasaki enthusiast who donated many old engine parts, and sold him a complete Voyager rolling chassis. A standard fork (with added preload spacers), wheels and discs are combined with extra-stiff Hagon shocks and a pair of modern six-piston Pretech front brake calipers to combat the bike's weight of approximately 770 pounds. Numerous dry runs using an electric motor meant Millyard wasn't surprised when the V-12 started up on the first press of the button, and ran well after minimal injection fine-tuning. But after a few weeks he had a setback when a big-end bearing seized, fortunately without causing further damage. After that he fitted phosphor-bronze bushings to the con-rods, and upgraded the lubrication system with a high-pressure feed to the small end (which had relied on oil mist). While the engine was apart he took the opportunity to increase the final drive ratio; the KZ1300's overengineered shaft-drive system is otherwise untouched.

All was working well when I arrived for a brief ride. From the fairly tall seat the Kawasaki seemed huge but curiously near-normal, though I soon became conscious of the hot rear cam cover between my shins, as well as the bike's sheer size and weight. The standard angular instrument panel is coupled with a swept-back KZ900 handlebar whose shape allows a typically upright riding position despite the extra tank length. Such was the V-12's low-rev torque that all it required was a hint of throttle to cruise along with the motor barely breaking a sweat.

Having ridden a couple of Millyard's previous Kawasaki creations, I expected the V-12 to be well-behaved and oil-tight, and it was. It was also massively torquey, responding cleanly when I wound the throttle from below 2000 rpm in top gear, which thanks to its recent gearing change was approximately 45 mph. The seductive low-rev burble changed to a snarl, and the Kawasaki surged smoothly forward like the world's most tuneful magic carpet.

Throttle response in the lower gears was slightly snatchy, but remarkably good considering the engine's complexity. I was keeping revs below 4000 rpm, yet the V-12 still had enough grunt to seem fast as well as relaxing. That rev limit gives a cruising speed of approximately 90 mph, which suited the big naked bike with its wide handlebars just fine. "I got it up to just under 100 mph the other day and it was effortless," Millyard says. "But I'm not really interested in opening it right up. I want it to sound good, be reliable and not leak oil."

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. At slow speeds there was no forgetting the bike's length, as well as all that weight. But the V-12 didn't wobble or weave despite a fairly worn rear Michelin. And the powerful six-pot front brakes slowed it with reassuring efficiency.

Millyard didn't mind trashing the rear tire with a few more burnouts after my ride, as he was planning to fit a new one before putting in some serious mileage over the next few months. He finished the bike too late for this year's Isle of Man TT, but is planning a trip there next June. "I could ride over the Mountain at 100 mph on it now. And since I've changed the gearing it gets over 15 mpg, which isn't bad because the original KZ1300 was very thirsty."

One thing he isn't planning to do is sell the V-12. "All my two-strokes are gone now. I've had a few inquiries about the V-eight, too, and might be tempted. But it would take a really silly offer before I'd sell the V-12. It took me so long to make—almost every evening for nine months. Now I just want to have some fun on it." Looks like he already is.

For more information on Allen Millyard and his wacked-out collection of bikes, e-mail him at Akawafives@tinyworld.co.uk.