The Germans Tried To Reinvent The Motorcycle Using A Rotary Engine And It Was A Hot Mess

If you’re a motorcyclist today, you have access to a stunning variety of engines from the humble V-twin to a turbine, but what you won’t see is a rotary. But that’s not because it hasn’t been tried before. Rotary-powered motorcycles seem to be cursed and one of them, the Hercules W-2000, seemed to have made little, if any, sense. Here’s this for an elevator pitch? Would you spend more money for a motorcycle that’s slower and less reliable than the competition? That’s essentially what the German manufacturer Hercules brought to the table. [Ed Note: But it was cool. -DT].

The wild thing about rotary-engine motorcycles is that there have been quite a few of them throughout history. Back in December, I wrote about buying a 1976 Suzuki RE-5, the Japanese motorcycle manufacturer’s failed experiment to build a better motorcycle. Suzuki burned bikeloads of money to make a better rotary engine, just for it to fail so hard that it’s rumored that the marque dumped spare parts into the ocean.

Nuremberg-based Hercules was notable for having created the first mass-produced rotary motorcycle a few years before its contemporaries. Rotaries were seen as the future of motorcycling. Yet, the Hercules W-2000 was confusing as it offered riders less for more money.

It Leads Back To One Man

There have been all sorts of rotaries throughout history, from the spinning Dorito in my Suzuki RE-5 to the million angry bees housed under the hood of your Mazda RX-8. No matter what brand name is on your rotary, it owes much of its existence to some unfortunately dark history.

German engineer Dr. Felix Wankel is credited with coming up with the idea for the rotary, also known as the Wankel engine, in around 1919 when he was just 17 years old. Wankel started building prototypes years later and finally earned a patent in 1929. Wankel’s development then slowed until he joined the Nazi Party and its Aeronautical Research Establishment during World War II. There Wankel would continue his work on his engine. Reportedly, the Nazis believed Wankel’s engine could give them an advantage in the war. Later, he’d arrive at NSU Motorenwork AG. By 1957 the rotary was no longer just a proof of concept but Wankel had running prototypes. Felix and NSU earned more patents and were quick to license out the technology.

Wankel is the inventor of the rotary gasoline engine, but the idea of the rotary sprouted up hundreds of years before him. Ramelli invented a rotary-piston-type water pump in 1588 while James Watt had a rotary steam engine in 1769. Though, it’s perhaps notable that neither of those earlier designs resemble the spinning triangles of the Wankel.

In theory, rotary engines have a lot going for them. Wankel engines have fewer moving parts than an equivalent piston engine. Their design also allows them to take up less space than an equivalent piston engine. Yet, because a rotary completes three full Otto cycles (intake, compression, combustion, exhaust) per rotation, a little 300cc rotary could produce the kind of power a piston engine of double the displacement puts out. Further, Wankel engines are nearly turbine engine-smooth with a broad rev range.

Again, in theory, a rotary is the perfect motorcycle engine. I mean, who doesn’t want to get more power out of a smaller engine and also not have to worry about your hands going numb from vibration? As Engine Builder Magazine explains, fewer parts also mean that rotaries also have the potential to be more reliable than their piston counterparts. Put it all together and you start to see why a plethora of manufacturers dipped their toes into the Wankel pool decades ago, and why Mazda still gives the tech a chance even today.

Anyway, NSU started licensing out the Wankel to just about anyone who thought they could turn it into the future. A non-exhaustive list of those with a license to build Wankels included AMC, General Motors, Norton, Citroën, Daimler-Benz, Honda, Kawasaki, AvtoVAZ, Ford, Mazda, Curtiss-Wright, Yamaha, and Van Veen. The first production rotary car was the 1963 NSU Wankel-Spider. Curtiss-Wright was one of the first to get a license, but its application would be for aviation. Mazda was hot on the heels of the Germans with its Cosmo, which made its debut in 1967.

As the Vintagent writes, rotary motorcycle development began in 1960 with Motorrad Zschopau (IFA/MZ) in Germany. MZ saw rotaries as potential replacements for two-stroke engines in cars and motorcycles. The company took three months to create a 175cc single-rotor Wankel motorcycle. Motorrad Zschopau is credited today for being the first to put a Wankel on two wheels. This engine was promising, too, as its 24 HP was double that of the firm’s existing 175cc piston two-stroke. It’s reported that MZ put at least 23,600 miles on its prototype and then built a second prototype.

However, MZ couldn’t resolve rotor tip seal failures or the fact that its rotaries ran really hot. Fixing these issues would have cost a ton of money and thus, the rotary couldn’t unseat the two-stroke engine. The Vintagent reports that engineers in East Germany produced a number of rotary engines destined to be saddled in vehicles like motorcycles and Trabants, but they just couldn’t be made reliable enough to replace what was already out there.

The Hercules

Fichtel & Sachs was reportedly the second licensee of the NSU Wankel, grabbing its rights in 1960. This one sounded like a great match. Fichtel & Sachs, a business that has been in operation since 1895, was then-known for its gasoline and diesel industrial engines, as well as its Saxomat semi-automatic transmissions. You might know the company best today for its Sachs clutch components or similar.

The rotary engine had potential in industrial applications, so Fichtel & Sachs took on a license as well. Three years after Fichtel & Sachs got its license to construct Wankels, it scooped up German motorcycle brand Hercules. This opened the door for Hercules to create a motorcycle nobody had seen before.

Fichtel & Sachs initially didn’t develop its version of the Wankel for motorcycles. Instead, it developed the single-rotor KM914 engine for use in snowmobiles, personal watercraft, and small aviation applications. In 1971, Cycle World reported that Sachs had already sent 20,000 of these engines to the United States for use in snowmobiles and aviation.

As Cycle World writes, the Hercules W-2000 made its first public appearance in 1970 during the West Cologne Autumn Motorcycle Show. The prototype at the show used the Wankel snowmobile engine and a transmission from a BMW R27. Ceriani telescopic forks at the front and a swingarm took care of suspension duties while the frame was a unique twin downtube setup that saddled the engine underneath. The motorcycle wasn’t much to write home about until you looked at that rotary. The Hercules W-2000 (sold as a DKW in the UK) entered production in 1974 and by multiple reports, the crowd merely went mild.

The Sachs KM914 has just 294cc of displacement and is fed from a 32mm Bing carburetor, but because a rotary fires three times for each rotation, engineers reportedly estimated that it would make the power of close to a 900cc four-stroke of the era. Some jurisdictions tax rotaries based not on their actual displacement, but the idea that it’s actually punching out the power of a bigger bike.

However, Cycle World reported that the Federation Internationale Automobiliste (FIA) felt differently. See, a four-stroke piston engine fires once for every two revolutions and is running 1:1 with its output shaft. Meanwhile, a rotary fires three times for every rotation, but runs 1:3 with its input shaft. There’s some math in there, but the FIA believed a rotary is roughly equivalent to a four-stroke of double the displacement, not triple.

However, Cycle World is quick to point out that this is all theoretical. In practice, manufacturers working with rotaries tuned the engines for reliability, not power. Early rotaries suffered from apex seal failures and way too much heat. Mazda had a whole development team dedicated to solving the rotary’s killer issues. NSU initially used graphite seals that cracked if ignition timing wasn’t perfect. Later, it so switched to cast iron apex tips that sealed against a cemented carbide rotor housing.

The result of trying to make a longer-lasting rotary meant the KM914 made just 23 HP at launch, or ten fewer ponies in the stable than a slightly larger 325cc Honda twin-cylinder four-stroke. The rotary spun perpendicular to the wheels, which required 90-degree bevel gears from the eccentric shaft to get power to the transmission and then to the rear wheel through a chain. Cycle World found the Hurcules W-2000’s 24.5 lb-ft of torque output equally unimpressive. That was a problem because as the magazine put it, horsepower may not have been a strong suit of this engine, but torque was supposed to be.

With that said, there were good notes in both of the reviews published by Cycle World in the 1970s. The magazine noted that the motorcycle was buttery smooth, especially above idle. The Hercules also had a power band that was wider than a four-stroke engine and that band was largely flat. In other words, the bike felt largely the same no matter if you were lugging it or making peak power.

Amusingly, the Wankel also never got to show off its other advantage on the Hercules. The rotary is supposed to be a compact engine, but the Sachs iteration drooped off of the motorcycle’s frame like the fuel pod of a vintage aircraft. Add the huge shroud for the engine fan and the cooling fins for the air-cooled engine and you have a rather chunky unit.

A Revolutionary Failure

The motorcycling press wasn’t kind to the Hercules. Cycle World didn’t paint a good picture. Here are a few paragraphs from its full review in 1976:

Gearing is pretty tall, about the same as a CB750 Honda’s. Indicated rpm at 60 mph is only 3750. Not bad. And it pulled up any hill we found in sixth, no problem, at 50-55. When it comes time to pass, though, a couple of downshifts will be necessary. Even so, performance is not spectacular, just adequate if the driver of the car you’re passing doesn’t stand on it at the same time. If he does, you lose.

On freeways, the Hercules is affected by rain grooves more than most machines. Same for cross winds, in spite of the low center of gravity. Cornering stability is excellent, however. Actually, the low center of gravity and tire profile encourages fast cornering; up to the machines ground clearance limit, it’s really nice both in steering and stability. Going left, the centerstand drags all too soon. It’s even possible to drag it in town if you’re in a hurry to beat a stoplight. Footpegs are rigid and are wide enough to make contact with the ground, as well. We really prefer folding pegs from both safety and clearance standpoint. If it weren’t for the limited ground clearance, handling on the Hercules would far exceed the capabilities of the engine.

The magazine felt that the 391-pound motorcycle was best as a commuting machine or maybe as something you might tour on due to the lack of vibration. However, other review notes include loudness and just terrible switchgear. We’ll get to that in a moment, but I have to stop at the loudness part for a second. When I first started my Suzuki RE-5, I was surprised that it basically drowned out all other noises. Standing next to a running Suzuki RE-5 is like standing next to a vintage airplane running up its engines. The Hercules W-2000 is said to be quieter, but only just.

Anyway, Cycle World continues:

Electrics are bad. The tach is electric and wanders too much. It also reads about 4000 rpm with the engine off if the ignition switch is turned to the night position. In the night position, the lights remain on at all times. In the daytime position, the headlight remains on except when the machine is in neutral. The horn is not loud enough; and the battery goes dead if the engine does not start quickly.

Switches are worse. They are Italian because the German switches the factory intended to use were all purchased by BMW. Besides being confusing and poorly labeled, you can’t operate the starter button with a heavily gloved hand. You can’t reach the turn signals without removing your hand from the throttle. Sometimes when you hit the turn signal switch, you also hit the engine kill switch. Et cetera.

One final annoyance is the centerstand. For its size, this is the most difficult bike to get up on the stand that we’ve ever encountered. It’s at least as difficult as a poorly designed 750 stand.

More modern reviews have been kinder to the Hercules. Vintage vehicle owners are seemingly more willing to put up with quirks for that unique experience. I know I am. Motorcycle USA has a review from 2008 that is a totally fun read:

Right from the off, the engine ran at science fiction hot temperatures and after a few rides the exhaust headers had been blued to oblivion. The dealer had given me dire warnings that if I over-revved the motor then the rotary tips might flutter and then break. If this happened, the tip would score the rotary housing and the next step thereafter was a trip to the bank to pay for the rebuild. Contrast this state of affairs with how easy it is to repair an abused two or four-stroke engine.

The problem – and you will note how many times the word “problem” has occurred in this story – was that the six speed gearbox was rubbish and missed gears were all too common. If a gear was missed with the motor being worked hard it would spin round well past the very modest rev. limit of 6,200rpm and then there was the big thrill to see if the engine had just been destroyed. In practice, I preferred to change at a lowly 5,500rpm and so save the wear and tear on my heart.

Something else was noted in those reviews, and it was the fact that while the rotary engine didn’t care about the quality of fuel used or the quality of gear oil, it was really specific about injection oil. Early Hercules W-2000s ran on premix, but examples from 1976 and later had an injection system for ease of use. Shell Rotella SX 30 was the best oil, but wasn’t sold in America. The engine would run for a limited time on other oils, but the engine’s seals would char, you would lose compression, and eventually, the engine would just stop running. So, running the right oil was a must if you wanted the engine to actually work.

Sadly, the Hercules didn’t set the motorcycling world on fire. As it turns out, there weren’t many people willing to spend $1,900 ($12,734 today) on a motorcycle that couldn’t hit 100 mph and would kill itself if you didn’t run an exact oil you couldn’t even buy in the United States. Even its 40 mpg fuel economy was just okay. Later Hercules W-2000 motorcycles got power bumped up to 32 HP, but even that wasn’t enough. The fact that some insurers and jurisdictions used swept volume calculations to treat these like larger bikes didn’t help.

Reportedly, just 1,784 units were built between 1974 and 1977, making a Hercules W-2000 a rare motorcycle anywhere in the world. It also means the Hercules W-2000 was only the first of many rotary motorcycles to fail throughout history. Those failures include my own Suzuki RE-5.

As of right now, I’ve found just one Hercules W-2000 for sale within reach of the United States. It’s pictured above! There is a 1976 Hercules W-2000 for sale in Airdrie, Alberta, Canada, for the equivalent of $8,029 USD. It looks to be in great condition and as of right now, you aren’t likely to find another for sale in North America. I couldn’t even find any for sale in the UK.

I think the incredible thing is that despite many documented failures to successfully market rotaries, numerous companies still tried, anyway. I’m glad they did because otherwise, I wouldn’t own such a weird motorcycle. It’s also awesome to see Mazda still trying decades after everyone else gave up. But if you’re looking for a different way to ride this summer, try a rotary.

(Top Image: RM Sotheby’s)