Kawasaki W800 Cafe Links Modern Engineering To Motorcycling’s Past

An air-cooled parallel twin designed to live a long, stress-free life

2019 Kawasaki W800 Cafe
As with classic British twins, you can see through the 2019 Kawasaki W800 Cafe, through its wire-spoked wheels, under its induction system, ahead of its cylinders. That’s how motorcycles always used to be—transparent.Kawasaki

This Kawasaki, the most recent in the Japanese manufacturer's half-century series of four-stroke parallel twins, is an entirely modern 360-degree-firing plain-bearing engine that will probably last forever at its very moderate level of stress. It has a great 1-1/2-inch Gerotor oil pump to keep its crankshaft journals, balancer, shaft-and-bevel-gear camshaft drive, and overhead cam plus rockers well-supplied with oil.

Yet there is also something familiar from long ago, so I quickly looked up performance and other data for Triumph’s classic twin-carburetor, two-valves-per-cylinder Bonneville 650, the bike that arm-wrestled Harley-Davidson’s 55-inch Sportster for the paychecks of America’s sporty big-bike riders.

Point for point, there is near identity between the latest W800 and the great T120 "Bonnie" of yesteryear. Power in both cases is 46 hp at 6,500 rpm (46.2 hp at 6,200 rpm for the W800 Cafe on the Cycle World dyno), and both employ the moderate "run-on-anything" compression ratio of 8.4:1. Both are air-cooled with real, as opposed to the present retro fashion for faux, cooling fins. Peak torque is cited as 44.1 pound-feet at the moderate rpm of 4,500. And this 800's torque zone is wide, remaining within 90 percent of peak from 3,500 to 6,000 rpm; turn the throttle and accelerate, without constant shifting.

The W800’s paired intake valves, by closing near bottom center, keep all that charge in the cylinder to generate remarkable low-end torque.

How is that easy driveability, that low rpm of peak torque, achieved? Strangely enough, it is a direct result of this engine's four valves per cylinder. We usually associate four valves with super rpm and sportbikes with their peak torque up at 10,000 rpm. But the unique thing about four valves is that, being as light as they are, they can be punched open and then gently closed a lot faster than can the bigger "stoppers" of a two-valve head. That means four valves can flow plenty of air with much shorter valve timings. And short valve timings boost low-end torque by not staying open long after bottom dead center, not allowing the rising piston to push back out charge that was just sucked in a moment before (at higher revs, higher intake velocity prevents this back-pumping). The W800's paired intake valves, by closing near bottom center, keep all that charge in the cylinder to generate remarkable low-end torque.

Like enormous dinosaurs in a cooling climate, ever-heavier pistons felt selection pressure pushing them out of existence.

Kawasaki’s original 624cc W1 hit the US market in 1966 and was based on an old Meguro license to produce a BSA A7 look-alike. Both its pistons rose and fell together, giving a 360-degree firing order that generates the British-twin sound. Both pistons moving together makes an engine vibrate like a single, but as British twins were pumped up from their original 500cc displacement, their ever-heavier pistons made them shake harder and harder until, like enormous dinosaurs in a cooling climate, they felt selection pressure pushing them out of existence.

parallel twin
An engine for the ages? This 77.0mm x 83.0mm 773cc parallel twin is fuel-injected because it has become just too difficult to make carburetors pass emissions testing. Wide torque allows the bike to accelerate well with five transmission speeds.Kawasaki

In the modern engine idiom that shaking is easily handled. When you balance half of piston shaking force with crank counterweights, the result is a rotating imbalance of constant magnitude, turning opposite to the crank. To cancel any desired percentage of that, all you need is what W800 has: a contra-rotating single-lobe balance shaft spinning at crank speed and in the opposite direction.

If you care about engines, you are probably wondering right now why Kawasaki chose to give this one a single overhead cam driven by a towershaft with a pair of bevel gears at top and bottom rather than the usual cam chain. The usual cam-drive possibilities are these:

  1. Pushrods and rocker arms universally used on classic British twins. The objections are noise, frequent need for valve clearance adjustment, and limited rpm ceiling as a result of extra valve-train weight; for equal rev capability, a pushrod valve train requires roughly twice as much valve-spring pressure as does an overhead cam system.

  2. The usual Japanese solution has been chain-driven double-overhead camshafts—one cam for the intake valves, another for the exhausts—with some form of automatic chain-tension adjuster. As chains wear, accurate valve timing is lost, which is why Superbike teams of the 1990s were supplied with gear-drive kits. I love that gear-drive sound!

  3. DOHC driven by spur gears is the racing solution because, with either finger followers or inverted-bucket tappets, it gives minimum valve-train weight and therefore maximum valve control. But spur gears are expensive and noisy, so they aren't used for production designs. EPA sound meters are listening!

W800 Cafe chassis
The W800 Cafe’s chassis is a traditional twin-loop, twin-shock design, executed in equally traditional steel tubing. Drive to the 18-inch rear tire is by modern sealed chain, an element in the bike's $9,799 suggested retail price.Kawasaki
  1. Toothed rubber belt and cog pulleys. This was how Ducati eliminated the handwork once required to assemble Dr. Taglioni's shaft-and-bevel cam drive (selective-fit shims, checking tooth-contact patterns with Prussian blue, many trial assemblies, hours of work). Belts were great at first, even Rob "Mr. Superbike" Muzzy was interested in them in the early 1990s. But as valves had to be accelerated harder and harder in Ducati's Superbike program, belt life became so short that Ducati gave its ultimate V-twin, the 1199 Panigale, cam drives of steel chain.

  2. Weird and wonderful. Husqvarna's engineer Folke Mannerstedt developed his Excam system in 1927. Its cam oscillated back and forth rather than rotated, so it could be driven by a connecting rod from a half-speed shaft geared to the crank.

  3. Shaft and bevels—what Kawasaki chose for the W800—is a system that was widely used in aircraft engines of both world wars and which stuck in the minds of those exposed to it. As a result, Norton's Manx racing single and Velocette's KTT employed it. Why Kawasaki, why now? Maybe for two reasons: First, it's different, and identity is priceless today. Second, with its splined vertical driving shaft, there is no change in valve timing as the engine expands during warm-up and no noise. How did they get around "the Taglioni problem"? Uncounted millions of cars and trucks drive their wheels through shaft and bevels, all so accurately manufactured that no hand-fitting by elderly craftsmen in wire-framed spectacles is required.

The classic 1966 Triumph Bonneville had two ball main crankshaft bearings and plain-bearing connecting rods, all lubricated by a rather Edwardian up-and-down double-piston pump. The Kawasaki W800 has a fully supported, three-main-bearing crankshaft, and all bearings are of the plain-journal type, which give outstanding durability.

W800 Cafe
With its air-cooled, SOHC, eight-valve twin—46 hp and 44 pound-feet of torque—pulling 491 pounds (with a full fuel tank) plus rider, the W800 Cafe reached 60 mph in 5.1 seconds and covered the quarter-mile in 13.8 seconds at 95 mph.Kawasaki

Now, how about that air-cooling? We’ve seen Harley-Davidson, BMW, and even Honda circulate liquid coolant—oil or 50/50 water/antifreeze—around hot exhaust-valve seats to prevent high-temperature creep and leakage. Why doesn’t the W800 need this kind of help? Heat distortion can make it tough keeping four valves per cylinder properly sealed; the narrow bridge between paired exhaust valves is especially vulnerable.

A good way to compare the degree of severity of various engines is in terms of horsepower per square inch of piston area. On the W800, the number is 3.25. On the 1966 Triumph Bonneville, it was 3.75, but in the case of a 136-hp-claimed BMW R1250GS, it jumps to 5.44, or an increase of 67 percent. Okay, now I’m getting a glimmer of the heat problem. The W800’s low thermal loading and moderate compression ratio make air-cooling and four valves per cylinder compatible.

Here, just for fun, are a few more examples:

260-hp MotoGP engine: 8.13 hp/sq.-in.
Suzuki Hayabusa engine with 650-hp turbo kit: 20.31 hp/sq.-in.
BMW 1.5-liter Megatron 1,300-hp turbo Formula 1 engine: 33.00 hp/sq.-in.

The upshot of all this palaver about horsepower per square inch of piston area is that the W800 Cafe is designed to operate at a very conservative level of thermal stress and for a long time. It's just a regular motorcycle, not demanding to be ridden straight up, or to Patagonia, or to gritty urban bars. Ride it where you want to go. It's not a built-to-the-limit sportbike engine pushing 16,000 rpm or a giant twin busting itself to keep up with high-revving fours. It's just made to give a pleasing level of fun at low stress and for a long time.