The first production rotary-powered motorcycle, the Hercules W2000 was a techie's dream but faltered in the real world.
The Hercules W2000 was the first-ever production rotary engined motorcycle and for that reason deserves a place in history. It was also the first in a line of not undistinguished rotary engined motorcycling failures - not because it was an inherently bad bike but for the simple reason that engineers believed their own hype.
The great problem with all rotaries is that the clever engineers who design them are born with a mathematical ability that few of us ever achieve after a life-time struggling with a calculator and a computer spread sheet. They just know in their heart of hearts that the Wankel rotary engine is conceptually superior to dirty two-cycle engines and scarcely less inefficient four-strokes.
I once interviewed David Garside - the man behind the Norton rotary, which is perhaps the best ever Wankel-engined bike to reach production. He told me how he would come out of lectures at the School of Engineering at Cambridge University - rotary engineers are always brilliant - and play with the model they had on display.
It could be argued that the good Mr. Garside should have been chatting up pretty lady engineers, or mainlining on coffee and cream cakes in the manner of most sensible 20-year-olds, but the young David used to twirl the rotary shaft on the model and drool at its mechanical elegance.
So let’s look at what gave Mr. Garside the tingle in his mechanical loins. Through the eyes of a purist engineer a conventional four-stroke is a truly horrible thing. The problems begin with the piston which has to come to a complete stop at the top of every stroke. Then it has to start again and travel all the way to the bottom of the cylinder and stop once more. Stopping and starting is grossly inefficient and wastes a huge amount of energy.
A rotary engine is more efficient, but the practical application had problems.
The power the four-stroke engine produces is linear, not rotary, and therefore the energy from the piston travelling up and down has to be wastefully converted into rotary action in order to drive a wheel.
The four-stroke engine is full of expensive, fragile parts which offend the engineer’s sensitive eye. The powerplant is packed with valves, pistons, cams, springs and a myriad of other expensive items all of which waste power and cost a lot of money to make.
Two-strokes are fractionally better in that they have fewer moving parts, but their fuel consumption to power ratio is poor because of their inherent inability to burn all the hydrocarbons they have available for combustion.
Roll of drums and fanfare of bugles. What the world needs is a Rotary engine in which all the power is converted into rotary action.
This is what the Junior High School student’s best friend, Wikipedia, says:
"In the Wankel engine, the four strokes of a typical Otto cycle occur in the space between a three-sided symmetric rotor and the inside of housing. In the basic single-rotor Wankel engine, the oval-like epitrochoid-shaped housing surrounds a rotor which is similar to a Reuleaux triangle, a three-pointed curve of constant width, but with the bulge in the middle of each side a bit more flattened. From a theoretical perspective, the chosen shape of the rotor between the fixed apexes is basically the result of a minimization of the volume of the geometric combustion chamber and a maximization of the compression ratio, respectively. Thus, the symmetric curve connecting two arbitrary apexes of the rotor is maximized in the direction of the inner housing shape with the constraint not to touch the housing at any angle of rotation (an arc is not a solution of this optimization problem)."
Don’t you just love engineering types? Incidentally, this is one of the simpler descriptions of the Rotary engine.
Okay, in real life this is the deal. In the middle of a Wankel engine is the rotor which is rather like an equilateral triangle. For those of you who were reading "Cycle" during your math lessons (a week’s litter picking after school for you Melling!) an equilateral triangle is one where all the sides are the same length.
The Wankel engine’s rotary is very similar to an equilateral triangle but with slightly bulging sides.
If you placed a shaft in the absolute centre of the triangle it could be made to spin round in perfect balance. However, if the shaft were placed in one corner then the triangle would rotate irregularly. In fact, you could make it follow a path where it apparently rose and fell.
With just one moving part the Wankel rotary powerplant is an engineer's dream.
So far so good. Now imagine a long rectangle with rounded corners. In one side is a hole which lets in fuel and air. Next to it is another hole through which the burnt gas escapes.
A charge of fuel/air is sucked into the rectangle by the spinning action of the rotor. The shape of the rotor housing (the elongated rectangle) compresses the mixture and a spark plug ignites it. The resultant explosion pushes the rotor round and the burnt charge exits through the final hole.
Now isn’t that beautiful? There is just one moving part and the motor is both light and small. Theoretically at least, it is also cheap to manufacture. What more could one want?
The problems start because the Wankel Rotary engine is a patented design. It was first conceived by the German engineer Felix Wankel in the early 1950s, when he worked for NSU, and developed by another NSU engineer Hanns Dieter Paschke.
NSU then enforced complex, and expensive, licensing demands on every company which tried to develop the Rotary engine. This constrained creative development of the basic concept and no doubt dissuaded many manufacturers from purchasing a licence.
This was the commercial constraint. Technically, there was an equally big problem. The whole Rotary principle relies on a perfect seal between the tip of the rotor and the housing. This seal is essential to separate the fresh charge from the burnt gases and to allow both efficient compression and burning.
The tip has to follow the irregular path of the rotary housing perfectly and at high speed. Before reliable, high temperature ceramics were freely available this was a really demanding mechanical trick and many engines suffered with tip flutter which led to poor mechanical efficiency.
So this brings us to the Hercules - and the standard mistake of all Rotary engine advocates: it is this. Rotary fans seem always to look at current four-stroke power plants and compare their engines with these - forgetting that the finishing line is always being moved. This is a fundamental mistake because almost every year since 1876 four-stroke engines have improved dramatically.
Hercules were heavily constrained by their licence with NSU which meant that their Rotary engines were not allowed to produce more than 30hp. Hercules also faced the problem that by 1974 they lacked the infrastructure to build the new W2000 from their own component parts. The new model was a real kit bike special with bits bought in from Grimeca, Bosch and Sachs. What was produced in house was not a great testament to German engineering. On the contrary, the frame was a really rough affair and the paintwork was: "What can you do for $5?" rather than "Let’s make a really nice motorcycle."
Finally, insurance companies didn’t know what to do with the Hercules. Each lobe of the Hercules rotary engine has a volume of 294cc. Hercules argued that in practice the bike was a low powered, mid-range motorcycle and therefore ought to be insurable for almost nothing.
However, the insurance companies felt that the capacity of the rotary engine was to be measured in the same way as a conventional motor by calculating its total swept volume. So, instead of what was a low powered 250cc engine they insisted that the power plant was three times 248cc - a whopping 882cc. This was only 19cc less than the awesome 82bhp Kawasaki Z1 which was the hyper sports bike of the early 1970s.
The result was a sales disaster. Every buyer with an ounce of common-sense, or logic, avoided the Hercules like the plague and the bike sold only to real biking geeks who delighted in the absurdly quirky. And that’s why I bought one.
In fact, that wasn’t the whole truth. In my case, there was another even more eccentric reason. In 1975, I was doing a lot of road and track tests for magazines and a new, bigger, better, shinier bike arrived every couple of weeks. For my own use, I wanted something that all the other journos didn’t have. I wanted a Hercules Rotary.
In Britain the Hercules was badged as a DKW which was considered to be the stronger brand name. In truth, neither Hercules nor DKW had any real credibility in the biking world - or out of it for that matter. Like rotary engines, these were motorcycles for the true two-wheeled geek.
The Hercules rotary engine ran extremely hot and revving too high could lead to an engine rebuild.
Almost as soon as I signed the cheque, I began to wonder what I had done - and why. The Rotary started well enough and then settled down to a rather odd engine note. Perhaps the best analogy was an outboard motor engine at idle - not absolutely offensive but nothing to stir the soul either.
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.
Rotary ownership was not an experience which caused exotic dreams at night. The engine was surprisingly torquey and pulled very smoothly from low revs but it was not exciting. The Hercules handled okay and braked okay and ambled along okay and was generally a sort of okay bike in an okay sort of way. But merely okay does not sell bikes or breed customer loyalty.
Compared to its reliable Honda competitor, the W2000 didn't stand a chance.
In terms of physical size, and price, it was pitched directly at the Honda CB400F which was faster, smoother, vastly more reliable, cheaper to buy and insure and was much better finished. It was not difficult to see why the Hercules was a sales disaster and the Honda a huge success.
Later, there was to be a much better rotary in the form of the Norton designed by none other than that brilliant young engineer who had played with the model rotary engine at Cambridge University. But we’ll look at David Garside’s remarkable motorcycle on another occasion.
Now, Hercules W2000s are as rare as unicorn horns and why anyone should want to own one is beyond me. However, on the rare occasions when they do come up for sale they make ridiculous sums of money. In October of this year, the bike in our photographs made a breathtaking $6200 at Bonhams Auction. There’s no accounting for what excites bike fans!
Our thanks to Bonhams Auction for the loan of the W2000. Contact Bonhams at www.bonhams.com
or tel: (415) 861-7500