Old Bike Australasia: DKW Rotary - A different spin
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Old Bike Australasia: DKW Rotary - A different spin

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By OldBike - 15 July 2015
DKW Rotary

As the 1970s dawned, it seemed just about every major manufacturer was either working on or thinking about producing a motorcycle powered by a variation of the NSU/Wankel rotary engine. Honda built and tested a prototype, named the CRX, Kawasaki came up with the X-99 and built several ‘mules’, while Yamaha went even further and publicly released the twin-rotor RZ-201 at the 1972 Tokyo Motor Show. Meanwhile, in Germany, the giant Sachs/Hercules concern was seriously gearing up for production of the W-2000. Ironically, while the 1970s fuel crisis was one factor in the demise of the rotary concept, the fuel crisis of the 21st century could be a catalyst in its revival. Serious development is known to be taking place on hydrogen-powered Wankel-style rotaries, producing excellent results with virtually negligible exhaust emissions. However of the Japanese manufactures, only Suzuki perservered to the point of taking out and paying for a licence to produce the Wankel patent under licence.

The giant Hercules/DKW concern chose to plunge into the same pool as Suzuki – displaying no fewer than five examples of the air-cooled Fitchtel & Sachs snowmobile-engined W-2000 model at the 1973 Tokyo Show. All used two-stroke style pre-mix fuel and were products of a design that dated back to 1971. One had a Sachs tank badge and another a Hercules badge, using the single KC27 engine, another Hercules with a KM24 single and a shaft drive with BMW transmission. They also displayed variants with DKW and Victoria badges – all names owned by the conglomerate. An in-line, fully-working KM914 “Big Twin” rotary engine was also shown.

With over 40,000 examples of the basic power unit sold around the world in snowmobiles, boats, pumps and stationary industrial power plants, Sachs expected a smooth transition to motorcycle use, but when subjected to the needs of running in traffic and delicate throttle response, it was lacking in several respects.

As a prototype, Hercules simply fitted its existing Sachs KC27 petroil-lubricated motor into a shaft drive 250 BMW frame, and it worked.

The Wankel generally behaves more like  a two-stroke than a four-stroke. It shares with the former the lack of positive scavenging, which results in uneven running on light loads, and the lack of engine braking. Suzuki found these traits unacceptable, and set out to eliminate them by using a complex dual ignition system, whereby when under load, the plus fires at each rotor face. When the throttle is partly closed, the increased vacuum is detected, and the ignition system fires the plug only on alternate rotor faces. Hercules-DKW used exactly the opposite approach. As a prototype, Hercules simply fitted its existing Sachs KC27 petroil-lubricated motor into a shaft drive 250 BMW frame, and it worked. For the production version, it reverted to chain drive, with a transversely-mounted longitudinal gearbox. As the rotor shaft was located longitudinally, this necessitated a pair of bevels between the motor and the gearbox.

Hercules went too far in its attempts to produce a simple machine. Rather than face the complication of a separate oiling system, it stuck to petrol-oil mixture. This was not only unacceptable on the grounds of inconvenience, it resulted in much-reduced performance. To cool and lubricate the rotor and its bearings, the incoming charge first passed through the centre of the rotor, before being looped back through a very restrictive porting system into the peripheral inlet port. At the front of the engine, carried on the centre hub of the fan, sat the magnets for the 100W alternator and magneto, with ignition and lighting coils on a stator plate within the hub.

Predating the Suzuki by a few weeks, the W2000, badged as a Hercules, made its public debut at the Los Angles Hilton in September 1974. It took another three months before deliveries were made to dealers in the USA. Buyer resistance centred around the antiquated petrol-oil mix, and one year later an new model, fitted with oil-injection, was introduced. Sales took a sharp upturn but then, in November 1976, the factory abruptly stopped production, ostensibly because the model had fallen marginally short of the minimum accepted production quota. A string of newly-enlisted dealers were left frustrated, with plenty of customers but no bikes.

Chassis-wise, the DKW was impressive, with a tubular backbone frame supporting the underslung engine in Aermacchi style. 

In Australia, the W2000 came as a DKW, with tank styling and colour scheme seemingly stolen from, rather than based upon, a 1971-model Honda CB250. Chassis-wise, the DKW was impressive, with a tubular backbone frame supporting the underslung engine in Aermacchi style. Up front were Ceriani forks and a single 300mm Grimeca front disc with double-piston caliper. Spanish-made Bosch headlight and starter motor. The DKW came with a six months or 10,000 km warranty, but advertising brochures proudly stated that the engine should do 100,000 km before requiring any major rebuilds.

Generally the DKW can be flicked around effortlessly - it’s comfortable and the controls, seat height and pedals seem ideally positioned

Riding the W2000 is a totally unique experience, rather like half way between a two-stroke and four stroke, with a performance level approaching the Japanese 350s of the period.  There’s plenty of middle range torque, but no point in revving the engine hard, as the power stops dead at 6,000 rpm. You certainly notice the lack of engine braking into corners, but overall, the DKW handles and brakes exceptionally well. Ground clearance on the left hand side needs watching, as the centre-stand snags the deck quite easily, but generally the DKW can be flicked around effortlessly - it’s comfortable and the controls, seat height and pedals seem ideally positioned to me. If you’re looking for a classic that really is different, it’s worth thinking about a DKW…or a Hercules…or a Sachs.

Protect your DKW. Call Shannons Insurance on 13 46 46 to get a quote today.