What In The World?Let's face it-we motorcyclists have a pretty dismal opinion of diesel engines, usually derived from the painful consequences of encountering a road surface coated with oil carelessly dropped by a truck, or even one of the increasing numbers of cars powered by Rudolf Diesel's compression-ignition motor invented back in the 1890s. Since then, the diesel engine has become a mainstay of marine, locomotive, urban transport, road haulage and stationary use-indeed, any application where its inherent benefits of 30 percent lower fuel consumption, cleaner emissions and longer life, as compared to an equivalent internal combustion petrol engine employing the Otto principle (i.e., using a spark plug to light the fire), can sufficiently offset its disadvantages of increased noise, vibration, higher manufacturing costs, and greater weight and bulk. While permitting the use of cheaper, non-fossil fuels (Rudi ran his early engines on peanut oil!), diesel engines require a heavier, more robust construction, until now making them unsuitable for certain applications such as aircraft and motorcycles.
Germany's Neander Motors plans to change all that, thanks to a unique new 1430cc turbocharged parallel-twin diesel engine that's been developed for them by Rupert Baindl. The twin-crank 750cc BMR Supermono single, which actually got built and produced an amazing 115 bhp at 12,000 rpm, according to Rupi, then morphed into a projected 990cc four-con-rod parallel-twin MotoGP racer that never got past the CAD stage, and thence to the prototype of what promises to be the world's first turbo-diesel production motorcycle. Indeed, the incredible diesel device I found waiting for me to ride in the Bavarian countryside south of Munich, masquerading at a swift glance as an American-style cruiser with a big parallel-twin motor that could easily resemble Triumph's forthcoming 1500cc custom, is a bike literally unlike any other, and not only because of its choice of fuel. That's because the hefty 1430cc air/oil-cooled parallel-twin motor with 108 x 78.2 mm cylinders and 360-degree crank throws, employs twin crossways-mounted contrarotating crankshafts, coupled together by gears, and each carrying two steel con-rods (so, a total of four, two for each cylinder). Each pair of these jointly supports a lightweight three-ring steel piston with ultra-short skirts via twin staggered gudgeon pins, resulting in minimal piston side-thrust as on a conventional motor. This, in turn, reduces potential friction and wear, in spite of the high 16:1 compression ratio. The plain-bearing big end on each con-rod pivots on a bolted-on external outrigger sleeve attached to each geared crank, and the con-rods are internally drilled for extra lubrication, much like a Ducati superbike's.
Atop this very robust but innovative bottom-end layout sits an equally unique eight-valve DOHC cylinder head, with four radial valves per cylinder (35mm inlets, and 30mm exhausts) operated via bucket and shims by twin overhead camshafts. The central chain drive to these is taken directly off the forward crank to spin its companion camshaft, which is directly geared across the top of the motor to the other, rear, camshaft. However, unlike on the MV Agusta F4, which also boasts a radial-valve layout, the Neander motor employs the cylinder head format patented by Austrian engineer Ludwig Apfelbeck, and most notably used by BMW on its 1960s Formula 2 racing cars. Instead of inlet valves on one side and exhausts on the other, as on a conventional pent-roof head, the valves are paired diagonally-so, exhaust, inlet, exhaust, inlet, driven by conical cams. "Apfelbeck suffered many problems with his radial-valve layout," says Baindl. "It's very similar to Honda's RVFC system, and as soon as high revs were used, the rockers would fail. The problems got even worse when they short-stroked the BMW F2 engine for 1600cc, so I decided to use the Rotax conical-valve system, which does not use rockers.
The Neander's inlet tract is channeled vertically down the center of the head, between the two camshafts, while the four exhaust valves each feed into separate dedicated header pipes (two at the front of the engine and two at the rear), which give the illusion of the quite wide motor being a four-cylinder. They're jointly routed into a single Garrett turbocharger with intercooler, delivering 1.4 bar boost pressure to the airbox containing the 31mm throttle body, and thence into a three-way catalyst mounted down in front of the engine, before finally exiting via twin lowslung pipes either side of the motor. The direct-injection Bosch common-rail EFI employs a single six-hole top injector, but a fuel cooler located in front of the steering head is required to prevent the incoming charge from cooking owing to heat transfer from the combustion chamber.
Fitted with a unit-construction six-speed gearbox employing Aprilia RSV1000R ratios with multiplate dry clutch, gear primary and Gates toothed belt final drive, this unique powerplant weighing 238 lbs. dry, delivers a claimed 94 bhp at 4200 rpm at the crank, matched to a thoroughly tractor-like 175 Nm of torque at just 2600 rpm. But the Neander Turbodiesel's cycle parts are surprisingly conventional, with the parallel-twin motor slotted into a conventional chrome-moly tubular-steel spine frame designed by German custom specialist Gunther Zellner, with the engine underslung beneath. The frame's fully adjustable hlins cantilever monoshock rear end is quite radical by cruiser standards, however, matched to 43mm upside-down Paioli forks up front which are set at a kicked-out 31-degree head angle, with 109mm of trail, resulting in a rangy 1740mm wheelbase. Neander executive Lutz Lester says the company is looking at offering a 1950mm version when production of a first limited edition of 50 bikes is scheduled to start in March 2007, with a target price of $85,000 or euro 68,500, including tax.
OK, that's what the Neander is, but, why is it so? Even before the established theoretical advantages of burning diesel over gasoline, what are the purported benefits of a radical engine design quite unlike anything anyone has ever done before? Bottom end first, and here the twin contrarotating-crank layout, with appropriate counterbalancing, can obviously eliminate the gyroscopic effects of crank rotation on the handling, as well as cancel out both primary and secondary vibration is that offset cranks can allow a twin-crank motor to lengthen the inlet and power strokes, in terms of crankshaft rotation, compared to the compression and exhaust strokes. Lengthening the inlet stroke gives more time to draw in mixture and cool the piston crown, while a longer power stroke allows more time for the expanding gas to push on the piston. Shortening the compression stroke gives less time for heat to transfer, while reducing the exhaust stroke results in higher exhaust gas speeds and better scavenging. The bottom line of all this is more power, delivered more efficiently.