Steve Wilgoose’s KZ1000R-S1 Replica

Steve Wilgoose’s 1982 Kawasaki KZ1000R-S1 replica is an evolutionary tale if ever there was one.

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by Robert Smith
  • Engine: 1,136cc (Wiseco big bore kit) air-cooled DOHC inline four, 74mm x 66mm bore and stroke, 10.5:1 compression ratio, 127hp @ 9,000rpm
  • Carburetion: Four Keihin 33CR
  • Transmission: Gear primary drive, 5-speed constant mesh, 520 chain final drive
  • Electrics: 12v, Dyna 2000 electronic ignition
  • Frame/Wheelbase: Tubular steel cradle, 59.8in wheelbase (1,519mm)
  • Suspension: Telescopic front forks, twin rear shocks by Works Performance
  • Brakes: 13in (330mm) twin solid disc front, 9.5in (250mm) solid disc rear
  • Tires: 160/60 x 18in front, 110/80 x 18in rear, Metzeler Racetec RR- K1
  • Weight: 462lbs (209.6kg)
  • Seat height: 31.5in (800mm)
  • Fuel Capacity: 5.5 gal. (21.4ltr)

Evolution is a natural process that occurs over generations. But it also applies to this story about Steve Willgoose and his 1982 Kawasaki KZ1000R-S1 replica — it’s an evolutionary tale if ever there was one.

Z1000R Eddie Lawson Replica. It took him the rest of his life to achieve his goal by slowly piecing together the Kawasaki of his dreams.

At 17, Steve was just getting into riding track days on 2-stroke Yamaha RD350s. At the racetrack in Calgary, Alberta, Canada, where he was learning the ropes, Steve saw a seasoned racer show up on an Eddie Lawson Replica. For Steve, the bike was interesting because it was rare, expensive, and something of a large and daunting machine.

Originally from Calgary and now living on British Columbia’s Sunshine Coast, Steve left school at 15 and became a woodworker. Because of his love for dirt biking, however, he also gained some mechanical talent. After the dirt bikes, he dabbled with 2-stroke race bikes. Then, several other larger and faster machines entered his universe. But, as he says, he’d buy something, fix it, then get bored with it and sell it. But this 1982 Kawasaki KZ1000R-S1 replica won’t be going anywhere soon, he says.

Replica of a replica

The S1 itself was something of a replica, as it simulated the Kawasaki raced by Eddie Lawson to take the 1981 AMA Superbike Championship. When introduced in 1982, the S1 was a Kawasaki factory race bike sent to the U.S. for AMA Superbike racing, and only 29 were said to have been built. While Steve remembers the rare Eddie Lawson Replica from his own racing days, the S1 is an even more uncommon motorcycle, and it’s the one he wanted to recreate.

“My goal was to build a period correct 1982 KZ1000R-S1 race bike in street trim,” Steve says. “And that got started with a 1982 Kawasaki GPz1100 resto-mod I bought out of Ontario. It had been modified with 2008 Kawasaki ZRX parts such as the forks, brakes and wheels all scabbed onto it. I got it here and rode it a bit. It pulled strong, but I wanted more and soon got to work.”

Steve is a woodworker, and because of his affinity for wood, some of the custom parts he makes for his motorcycles are prototyped in the natural material before he crafts the parts in metal. We’ll get to an example of that, but as mentioned, it’s an evolutionary story in two parts; Steve basically built the bike twice.

Round one

The first time he built it, he started with the wheels. Kawasaki used three-spoke Dymag rims on the S1, but Steve preferred the look of seven-spoke Marvic magnesium wheels — an Italian made reproduction of the Morris mags originally used on Eddie Lawson’s works bike. He ordered a set, and then proceeded to strip the 1982 Kawasaki GPz1100 donor bike down to the bare frame. Modifications were made to help stiffen the frame and to raise the rear of the gas tank.

Up front, Steve initially installed a stock Kawasaki fork but realized it was too short for the correct “look” of the race bike. He proceeded to build up new forks, acquiring parts such as reproduction lowers from Japan. Some slightly extended tubes came from Frank’s Forks, while the replica triple tree came from the U.S. and rare internal damping rods were located in South Africa. To mate the AP Racing calipers to the fork legs, Steve prototyped mounting brackets out of wood.

“I cut them out and bolted everything up to see how it all fit,” he says. “Once I was happy with the fit, I got a block of aluminum and had a slot milled in, then I made the holes and cut out the shape on a metal cutting band saw before doing lots of file work and using an edge sander to make them match my wooden prototypes.” With the front suspension complete, including fitting a hollow titanium axle to mount the 3 x 18-inch Marvic mag, Steve turned his attention to the rear suspension. For this, he’d purchased a handcrafted swingarm from the same seller who had milled up the triple tree. The swingarm was made to accommodate the 4.5 x 18-inch Marvic wheel, and Steve had Sprocket Specialists in Utah machine up a custom final drive cog. Having searched for months for an original set of Works Performance shocks, Steve finally located a pair on eBay, bought them and had them rebuilt by a suspension specialist who’d built shocks for race teams in the 1980s.

The engine

The 4-cylinder 1,089cc engine of the GPz Kawasaki had already been modified for performance with a Wiseco big-bore kit, taking it to 1,136cc. To put his stamp on the powerplant, Steve removed the cylinder head and shipped it to Larry Cavanaugh of Cavanaugh Racing Heads in Pennsylvania for larger intake valves and superbike porting and polishing. Cavanaugh, who has unfortunately passed away since first working with Steve, also supplied a set of his race cams. When all of the pieces came back, Jason Penner at Penco Motorsports in Sechelt, B.C. installed the head and cam using a special gasket and heavy-duty APE studs and nuts to keep the high-compression engine together.

To match the larger intake ports, Steve enlarged the rubber carburetor mounting boots and installed 33mm Keihin CR carbs. The Kerker exhaust came with the project bike, but Steve fabricated correct-looking spring mount tabs and welder Jeremy Clement joined them to the header. After hearing about his project, a Kerker representative sent him the correct 1000R collars and springs to mount the exhaust system.

While the engine was out, Steve took the time to paint it with a 2,000-degree ceramic coating. He set up a spray booth in his shop, and painted the engine, exhaust system and handlebar controls.

Bodywork and more

Ryan Redman at Fred’s Autobody & Painting in Sechelt, B.C, painted the frame and he was also responsible for the bodywork, priming and painting the gas tank that Steve had modified with a bung for a breather, along with the fairing and tail section. Before the clear coat was applied, Fred Gower placed the decals.

An attempt was made to rescue the wiring harness that was with the bike, but Steve finally bought a new-old stock loom from an eBay seller. A couple of final touches included a custom-made seat cover from the U.K., and the rare side-louvered smoked brake lens came from Japan. Instead of reusing old fasteners, the entire bike was assembled with formed thread titanium studs and bolts.

At that point, Steve had been at the build for about two years and was doing some fine-tuning and putting miles on the machine. Although happy, he still wasn’t fully pleased with it. He knew he could do better.

Round two

The first time around, Steve had started with a GPz1100 frame — and that’s not the frame Kawasaki used to build the S1 race bike. The factory used a 1982 KZ1000 ‘”J” frame with 27.5-degree steering head angle to construct the racing machine, and Steve thought, “I’ve got a race engine, race wheels, and all of the other right parts, so let’s make it right.”

Steve tracked down a bare 1982 KZ1000J frame and, working with an S1 collector in Australia, got photos and detailed measurements in order to make all of the S1-specific race bike frame modifications. Off came the centerstand brackets and the passenger helmet lock, and steering stop tubes were welded in place together with the rear brake return spring tab. Another significant modification found on the S1 frame is how the rear of the engine mounts in the frame with a tube-type spacer braced to the subframe behind the left side cover. Machined up and welded in place, the brace is necessary to handle the engine’s horsepower that could, with serious application of the throttle, twist on the standard bolt and bend the fitting. For ease of use, Steve left the side stand mount on the J frame. With all of the modifications on the new frame completed, Ryan at Fred’s Autobody & Painting laid down the black paint. Next, Steve dismantled his first build, and swapped over the forks, swingarm, shocks and engine. To satisfy his obsessive attention to detail, Steve made another set of front brake caliper mounts, added S1 replica racing callipers sourced from Japan, and plumbed both front and rear brakes with racing lines sourced directly from Japan. Before the wheels went in place, Steve polished the rim edge to reveal a silver lip and installed Metzeler Racetec K1 tires.

When assembling the machine, Steve got out his magnifying loop and pored over period images of S1s to identify exactly how the fasteners were safety wired, and he recreated the feature on his build. A correct magnesium quarter-turn throttle went on the aluminum handlebars Steve sprayed in a black ceramic coating.

He replaced the Kerker exhaust from the first build with a race pipe bought from Japan. It is an exact replica of the real works pipe Rob Muzzy used for Lawson and Rainey’s race S1’s. Steve added the Kerker badge to it. A machinist fabricated an S1-style tapered timing cover to go over the Dyna 2000 electronic ignition pickup. An original S1 would have had points, but the Dyna ignition gives Steve a rev limiter and programmable maps to work with. “I also got a new seat out of Japan to replace the one I had on there,” Steve explains. “This one is either from an S1, or it’s a very good replica because it is heat seamed and stitched exactly where it should be.”

Many other little details were attended to, including adding the proper front master cylinder housing and headlight mounting ears; Celine Harmel at Burnaby Kawasaki helped him track those pieces down. “She spent many hours poring over old microfiche to help me get more super rare parts,” Steve says.

Getting ready for the road

With the S1 replica together, Steve set to work dialing in the engine. For that, Eric Kuwabara from Sudco offered plenty of tuning advice, and Cypress Motorcycles in Delta, B.C., helped tune the Kawasaki on their dyno. According to Steve, they spent two days working at it. With its Wiseco 1,136cc big bore kit, the Kawasaki engine pulls 127 horsepower at the rear wheel at 9,000rpm, and Steve says it’s still making power after that figure

“For me, a motorcycle was never really about transportation,” Steve says. “It’s always been about the thrill of the ride, and I like to ride something that keeps me on my toes and keeps me challenged. I can’t go very far out here, up and down the Sunshine Coast Highway, 60 or 70 kilometers each way, but the road is winding and twisty with plenty of off-camber corners.”

He concludes, “The power is amazing. It just pulls and pulls all the way to redline at 9,500rpm, and those massive brakes are the real deal. You can slow the beast down very easily. The way this bike handles, it’s unbelievable, it just falls into corners and the engine’s got an incredible sound with that replica Kerker system — you can’t miss it.” MC

Kawasaki W, H & Z: The Big Air Cooled Machines

Kawasaki W, H & Z is the story of the air-cooled “big” Kawasakis in definitive detail, researched and written in Japan with full factory cooperation. These models put the Kawasaki company on the map during the 1960s and 1970s, helping it survive a difficult era that saw hundreds of Japanese motorcycle makers reduced to just four. This title is available at the Motorcycle Classics store or by calling 800-880-7567. Item #9594.

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