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Auction price:  
US $500.00
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Item Location: 
Chicago, Illinois, United States
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Vehicle does NOT have an existing warranty
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Private Seller

Phone number, E-mail address, Skype etc.



Frame Number: 480005202

Engine Number: 7586300

In the 1970’s, with the
rotary craze in full swing, the Hercules Motorcycle Company turned out two
fantastic models of the W-2000 machine with the Wankel rotary engine.  This is a later oil-injected example.  No need to mix the gas and oil in the tank!

While the Hercules Rotary is rare to begin with, this version of the W-2000 is much rarer than the earlier pre-mix model, with approximately 100 examples being built before production ceased.  Please note that unlike any other Hercules
rotary machines for sale, this one is in perfect running condition.    

Please note this motorcycle comes with clear title. 

The condition of this
machine is completely original. 
Everything from the frame to the motor to the fenders is exactly the way
it came from the factory.    

I believe I am the third owner from new, but can’t be positive.  This machine has been a part of my collection
for some time and is ridden occasionally. 
The bike is stored in a temperature controlled environment throughout
the entire year. 

When I purchased this
particular machine, it was in the condition you see in the photos, but it did
not run.  I went through the entire machine
and got everything working.  All of the
major engine, transmission, and braking components are operational. 

The tires are in good condition and are most likely original to the machine. 
The brakes have also been completely rebuilt, front and rear. 

The engine and
transmission are original and are in perfect running condition.  The bike is very easy to start.  A new battery was also recently installed.     

The paint is original
and in very nice condition, considering the age of the machine.  The seat is original and is also in very nice
condition down to the pan, which is also original.

The Hercules on the road
is very easy to handle, and rides down the road tight, with no shakes,
shimmies, or rattles.  It shifts and
accelerates smoothly and holds the road as it should.  

There is absolutely
nothing that needs to be done to this machine to ride, show, and enjoy it.  The new owner will have a fantastic and
incredibly rare original survivor machine that can be ridden and enjoyed as
well as shown at any vintage motorcycle show. 

I have a rotary motorcycle
collection made up of Hercules pre-mix and oil injected machines, as well as
Suzuki RE-5s, so if you have specific rotary questions, just want to learn
more, or are looking for something in particular, please let me know. 

I’m also always looking
for other vintage motorcycles to add to my collection, so if you have something
interesting to share, please contact me. 


The description of this
motorcycle is written to the best of my knowledge.  However, I am by no means an expert on
Hercules motorcycles.  Please don’t
hesitate to ask for more photos and, if possible, come and look in person
before the auction ends.  ALL SALES ARE
FINAL!  If you have any questions, please
contact me before the auction ends.

If you have any
questions, please contact me.  If you
live close to Chicago, I encourage you to come and inspect the Motorcycle in

In an effort to protect
the eBay user information and to help ensure the authenticity of correspondence
between sellers and bidders, eBay’s new listing format does NOT display any
bidder information.  Nevertheless, I
STRONGLY encourage bidders to contact me directly to answer questions or to
verify correspondence.  Seller reserves
the right to not accept bids or sell the vehicle to anyone with a zero or
negative eBay feedback rating.

This motorcycle is being
sold as is, where is with no warranty, expressed, written or implied unless
there is a warranty in effect from the factory. 
The seller shall not be responsible for the correct description,
authenticity, genuineness, or defects herein, and makes no warranty in
connection therewith.  No allowance or
set aside will be made on account of any incorrectness, imperfection, defect or
damage.  Any descriptions or
representations are for identification purposes only and are not to be
construed as a warranty of any type.  It
is the responsibility of the buyer to have thoroughly inspected the motorcycle
and to have satisfied himself or herself as to the condition and value and to
bid based upon that judgment solely.  The
seller shall and will make every reasonable effort to disclose any known
defects associated with this motorcycle at the buyer's request PRIOR to the close
of sale.  Seller assumes no
responsibility for any statements regardless of any oral statements about the

Please remember that
your bid constitutes a legally binding contract to purchase this item.  If you require an inspection, have it done
prior to bidding.  I strongly encourage
all bidders to inspect the motorcycle personally or enlist the services of a
professional inspector prior to placing a bid. 
After the sale, inspections are not recognized as a contingency to
completing your obligation to your winning bid. 
If there are any questions regarding the above terms, please e-mail
prior to bidding.

Please do not waste my
time or yours bidding on an item you do not intend to pay for.  If you bid on this motorcycle and win, you are expected
to pay and pick it up in a timely manner!

I welcome ALL
international bidders and am happy to assist with making shipping
arrangements.  I can also arrange crating
for shipment on my end for a nominal extra charge.  If you are an international buyer, I
understand it can take some time to arrange shipping, so I do not mind keeping
the motorcycle for a longer period of time until pick up.  Please contact me before the sale ends, if
possible, to discuss the specifics.

Thanks for your

more on the Hercules motorcycle company and the W-2000 Rotary, please read on past the photos…

Hercules W-2000 Specifications: 

Engine: 294cc air-cooled single rotor Sachs
Wankel, 8.5:1 compression ratio, 32hp @ 6,500rpm

Top speed: 90mph

Weight (dry): 381 lb (173kg)

Price when new: $1,900


Hercules was a brand of motorcycle manufactured
in Germany until 1996.

The Hercules Company was founded in 1886 and
began producing motorcycles in 1904. It was merged with Zweirad Union after
being purchased by ZF Sachs in 1963.

In the 1950s and 1960s Sachs was the largest
European fabricator of two-stroke motorcycle engines. Many of these engines
were used in the Hercules line of small motorcycles, scooters and mopeds.

In 1974 Hercules became the first company to
offer a Wankel-engined motorcycle for sale to the general public. A prototype
was first shown in 1970 at the West Cologne Fall Motorcycle Show to a mixed
reception, and the production bike was sold as a Hercules product except in the
United Kingdom, where it was marketed as a DKW motorcycle. The W-2000 had a
single-rotor air-cooled engine of 294cc that produced 23 hp, later increased to
32 hp. Cooling was by a large fan placed in front of the engine (and the
slipstream breeze while riding) and engine lubrication was by manually adding
oil to the fuel in the tank.

In 1976 Hercules launched the W-2000
Injection in which engine lubrication was from a separate oil tank via a pump.
It had 18-inch wheels, a front disc brake and a rear drum brake. According to a
March 1976 review in Cycle World, the handling was good but the bike's low ground
clearance limited its cornering ability. That review also declared the W-2000
to be a daily commuting bike, not a sport motorcycle.

Hercules introduced a rotary-powered dirt
bike (the KC-30 GS Enduro) in May 1975, but the model failed to sell due to its
high price ($2,900).

The Fichtel & Sachs single-rotor engine
of 300 cc swept-volume as used in the Hercules – the only commercially
available engine at the time – was used as a basis by BSA's project engineer
David Garside in the early 1970s when designing a twin-rotor motorcycle engine
of 600 cc, which reached production as the "Norton Classic".


The following is an excerpt from Motorcycle

A Rare Machine:

The Hercules W-2000 is referred to as the
first mass-produced Wankel rotary-powered motorcycle. Envisaged in 1919 by
German engineer Felix Wankel, the rotary power plant was thought by many to be
an ideal engine. The Wankel rotary had far fewer moving parts than a
four-stroke engine, and was theoretically more efficient.

But it wasn’t until 1957 that Wankel, working
with NSU, built his first running prototype rotary engine. The transportation
industry took notice of this new engine; from aircraft manufacturers to
automakers to motorcycle builders, everyone seemed interested in the new
technology. One of the first to license the Wankel technology was Germany’s
Fichtel & Sachs, at that time Europe’s largest producer of two-stroke

In the 1950s, German motorcycle maker
Hercules used Sachs lightweight two-stroke engines to power their many
different motorcycles, mopeds and scooters. Sachs purchased Hercules in 1963,
and eventually merged with the Zweirad Union, which included the DKW brand.  

Hercules developed the W-2000 using the Sachs
rotary engine in the late 1960s, and a prototype machine was first shown at the
1970 West Cologne Fall Motorcycle Show. Reaction was mixed: “Should it be
hailed as a great breakthrough, or a temporary mechanical diversion?” mused Dan
Hunt in his opening paragraph about the prototype Hercules rotary in the
January 1971 issue of Cycle World.

According to the article, 20,000 of the 294cc
Sachs rotary engines found in the prototype W-2000 had already been used in
U.S.-produced snowmobiles, and another version of the engine was used for
powering small aircraft. In the prototype, Hercules borrowed a 4-speed gearbox
and shaft drive from a BMW R27 single.


How the Rotary-Powered Motorcycle Works:

When Hercules officially launched the W-2000
in 1974 (sold as a DKW in the U.K. because a bicycle manufacturer already had
rights to the Hercules name), the BMW gearbox had been replaced with a 6-speed
unit with chain final drive sourced from a Penton 400 dirt bike. A set of bevel
gears transferred power from the rotary shaft through 90-degrees to the transmission
mainshaft, and the clutch was a seven-disc affair running in an oil bath. 

Of course, what is of primary interest is the
Sachs rotary engine, which used a single spark plug firing a single rotor with
apex seals.

As explained in the May/June 2011 issue of
Motorcycle Classics in an article about Suzuki’s RE-5 rotary-powered motorcycle
(effectively identical in principle): “The rotor’s tips seal against the
housing to form combustion chambers. Instead of a crankshaft, a rotary uses an
eccentric shaft with the rotor riding on the eccentric. A stationary gear on
the end of the eccentric shaft keys the rotor to the eccentric shaft.
Combustion pressure pushes the rotor away from the combustion face, causing the
eccentric shaft to rotate. The shaft’s eccentric defines the throw of the rotor
while the stationary gear defines the rotor’s position on its axis. As the
rotor spins, its axis shifts, causing the rotor to orbit and alter the
combustion chamber for intake, compression, ignition and exhaust phases.”

When first introduced, the Sachs engine was
rated at 23 horsepower, a figure that was later improved to 32 horsepower.
While listed at 294cc, for comparison to a piston engine that figure, in
theory, should be multiplied by two for a 588cc capacity: A single-rotor Wankel
produces one power stroke every crank revolution, whereas a single-cylinder
4-stroke requires two crankshaft rotations for each power stroke.

Fuel and air are mixed in a 32mm Bing
carburetor, and a single exhaust header splits into two under the engine and
feeds two mufflers, one on each side.

Unlike the Suzuki RE-5, which uses
liquid-cooling to help dispel the great heat generated by a rotary, the
Hercules W-2000 relies solely on a large axial fan at the front of the engine —
and, of course, the cooling breeze of the slipstream once underway.

The running gear consists of a tubular steel
frame with twin front downtubes that bend back and run over the top of the
engine. As a result, the Sachs rotary appears to hang from the frame, although
it’s also supported at the rear.

The front forks are Ceriani with 4.5 inches
of travel, and the rear swingarm is damped by adjustable preload Ceriani

The Hercules wears 18-inch wheels at both the
front and rear, and the front brake is an 11.8-inch disc, while the rear is a
7-inch drum.

Period tests of the Hercules give the machine
credit for its cornering stability, but fault the 6.5-inch ground clearance as
a major detractor in its cornering ability.

“If it weren’t for the limited ground
clearance,” Cycle World said in its March 1976 review, “handling on the
Hercules would far exceed the capabilities of the engine.”

Cycle World said the W-2000 would burble
along at an indicated 60mph, and would climb a hill in sixth gear at 50 to
55mph, but said it took at least one and most probably two downshifts to
overtake a car on the highway: “…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,” Cycle World said.


Original distribution of the Hercules W-2000:

While the W-2000 might well have been the
first rotary-powered motorcycle offered publicly through a dealer network, he
thinks it was built solely to test consumer acceptance of a rotary-powered two-wheeler.
The first container of 40 Hercules W-2000s — 34 with red tanks and 6 with
yellow — arrived in the U.S. in January 1975 and was delivered to Rotary
Recycle U.S.A. The Rotary sales team visited dealers across the U.S., espousing
the virtues of the Wankel. New dealers were enlisted, and rising orders for the
$1,900 rotary showed there was some interest. 

In May 1975, Hercules introduced the KC-30 GS
Enduro rotary-powered dirt bike, and shipped two to Rotary Recycle. Although it
generated great excitement, the KC-30’s $2,900 price tag killed any sales of
the model. And by the end of summer, sales of the Hercules W-2000 had slowed to
a trickle, perhaps because Hercules had announced an oil-injected model was
coming for 1976. Early machines required pre-mixing the oil and gasoline.

The W-2000 “Automix” are the 199 oil-injected
1976 machines produced. Of those 199, it is unknown how many landed in the U.S.
Unlike the Suzuki RE-5, there is no crankcase oil used in the W-2000 engine,
and it does not run two-stroke oil. 

The RE-5 has five different cavities for four
different fluids, the oil pump and the points are all running off of something
else, and the carburetor is a bit complicated. The Hercules, by comparison, is
very simple, with a fan in the front, and the ignition runs off the same shaft. 

The Hercules sounds like a cross between a
two-stroke and a four-stroke. On the road, low-end torque is a bit lacking, but
with the 6-speed gearbox he can keep the W-2000 moving along on the highway.

Just 1,784 of the rotary Hercules motorcycles
were built, the plug being pulled not because they weren’t well made, but
because they missed their set monthly sales quota by 25 units.


Hercules W-2000 press reports:

“Surprisingly attractive in a Teutonic way,
it is solidly built. The seating is comfortable and the handling is slow and
graceful. It is hardly a sporting machine, nor does it have sporting
performance, But it is flexible, smooth, comfortable and would undoubtedly
prove a pleasure on extended journeys.” – Cycle World, January 1971

“It’s not one of those bikes that offer
spirited performance. Speed is simply built up mile per hour by mile per hour.
If you are over 4,000rpm, there really isn’t much advantage to shifting. And
cornering is effectively limited by conservative ground clearance. So, the
Wankel 2000 is not a bike for sport. It’s a bike for daily commuting.” – Cycle
World, March 1976

“Sixth gear at 65mph is perfect. But if you
try to ease down to legal speed, the tach drops from 4,000 to about 3,200 and
the engine gets rough. Gearing down doesn’t help, but adding power does. You
get the impression that the Hercules doesn’t agree with our politicians about
how fast we should travel.” – Cycle, June 1976

to Motorcycle Classics and Cycle Magazine for the preceding articles and


So what exactly is a rotary engine???  Check out the articles below to find out more... 


Wankel Engine:

The Wankel engine is a type of internal
combustion engine using an eccentric rotary design to convert pressure into a
rotating motion instead of using reciprocating pistons. Its four-stroke cycle
takes place in a space between the inside of an oval-like epitrochoid-shaped
housing and a rotor that is similar in shape to a Reuleaux triangle but with
sides that are somewhat flatter. The very compact Wankel engine delivers smooth
high-rpm power. It is commonly called a rotary engine, though this name applies
also to other completely different designs.

The engine was invented by German engineer
Felix Wankel. He received his first patent for the engine in 1929, began
development in the early 1950s at NSU, completing a working prototype in 1957.
NSU then licensed the concept to companies around the world, which have
continued to improve the design. It is the only internal combustion engine
invented in the twentieth century to go into production.

Thanks to their compact design, Wankel rotary
engines have been installed in a variety of vehicles and devices including
automobiles, motorcycles, racers, aircraft, go-karts, jet skis, snowmobiles,
chain saws, and auxiliary power units.


In 1951, the German engineer Felix Wankel
began development of the engine at NSU Motorenwerke AG, where he first
conceived his rotary engine in 1954 (DKM 54, Drehkolbenmotor). The KKM 57 (the
Wankel rotary engine, Kreiskolbenmotor) was constructed by NSU engineer Hanns
Dieter Paschke in 1957 without the knowledge of Felix Wankel, who remarked “you
have turned my race horse into a plow mare“. The first working prototype DKM 54
was running on February 1, 1957 at the NSU research and development department
Versuchsabteilung TX. It produced 21 horsepower; unlike modern Wankel engines,
both the rotor and the housing rotated. In 1960 NSU (the firm the inventor
worked for) and the US firm Curtiss-Wright signed an agreement where NSU would
concentrate on the development of low and medium powered Wankel engines and
Curtiss-Wright would develop high powered Wankel Engines, including aircraft
engines of which Curtiss-Wright had decades of experience in the design and
production of.

Considerable effort went into designing
rotary engines in the 1950s and 1960s. They were of particular interest because
they were smooth and quiet running, and because of the reliability resulting
from their simplicity. An early problem of buildup of cracks in the epitrochoid
surface was solved by installing the spark plugs in a separate metal piece
instead of screwing them directly into the block. A later alternative solution
to spark plug boss cooling was provided by variable coolant velocity scheme for
water-cooled rotaries which has had widespread use and was patented by
Curtiss-Wright, with the last-listed for better air-cooled engine spark plug
boss cooling. These approaches did not require a high conductivity copper
insert but did not preclude the use.

Among the manufacturers signing licensing
agreements to develop Wankel engines were Alfa Romeo, American Motors, Citroen,
Ford, General Motors, Mercedes-Benz, Nissan, Porsche, Rolls-Royce, Suzuki, and
Toyota. In the United States, in 1959 under license from NSU, Curtiss-Wright
pioneered improvements in the basic engine design. In Britain, in the 1960s,
Rolls Royce Motor Car Division pioneered a two-stage diesel version of the
Wankel engine.

Also in Britain, Norton Motorcycles developed
a Wankel rotary engine for motorcycles, based on the Sachs air-cooled Wankel
that powered the DKW/Hercules W-2000 motorcycle, which was included in their
Commander and F1; Suzuki also made a production motorcycle with a Wankel
engine, the RE-5, where they used ferrotic alloy apex seals and an NSU rotor in
a successful attempt to prolong the engine’s life. In 1971 and 1972 Arctic Cat
produced snowmobiles powered by 303 cc Wankel rotary engines manufactured by
Sachs in Germany. Deere & Company designed a version that was capable of
using a variety of fuels. The design was proposed as the power source for
United States Marine Corps combat vehicles and other equipment in the late

Mazda and NSU signed a study contract to
develop the Wankel engine in 1961 and competed to bring the first Wankel
powered automobile to market. Although Mazda produced an experimental Wankel
that year, NSU was first with a Wankel automobile on sale, the sporty NSU
Spider in 1964; Mazda countered with a display of two and four rotor Wankel
engines at that year’s Tokyo Motor Show. In 1967, NSU began production of a
Wankel-engined luxury car, the Ro 80. However, problems with apex seal wear led
to frequent engine failure, which led to large warranty costs for NSU, and
curtailed further Wankel engine development.

Mazda, however, claimed to have solved the apex
seal problem, and was able to run test engines at high speed for 300 hours
without failure. After years of development, Mazda’s first Wankel engine car
was the 1967 Cosmo 110S. The company followed with a number of Wankel (“rotary”
in the company’s terminology) vehicles, including a bus and a pickup truck.
Customers often cited the cars’ smoothness of operation. However, Mazda chose a
method to comply with hydrocarbon emission standards that, while less expensive
to produce, increased fuel consumption, just before a sharp rise in fuel
prices. Mazda later abandoned the Wankel in most of their automotive designs,
but continued using it in their RX-7 sports car until August 2002 (RX-7
importation for Canada ceased with only the 1993 year being sold. The USA ended
with the 1994 model year with remaining unsold stock being carried over as the
‘1995’ year.). The company normally used two-rotor designs, but the 1991 Eunos
Cosmo used a twin-turbo three-rotor engine. 

In 2003, Mazda introduced the
Renesis engine with the RX-8. The Renesis engine relocated the ports for
exhaust and intake from the periphery of the rotary housing to the sides,
allowing for larger overall ports, better airflow, and further power gains.
Early Wankel engines had also side intake and exhaust ports, but the concept
was abandoned because of carbon buildup in ports and side of rotor. The Renesis
engine solved the problem by using a keystone scraper side seal. The Renesis is
capable of delivering 238 hp (177 kW) with better fuel economy, reliability,
and environmental friendliness than previous Mazda rotary engines, all from a
nominal 1.3 L displacement, however this was not enough to keep up with ever
more stringent emissions standards. Mazda ceased production of their Wankel
engine in 2012 after the engine failed to meet the Euro 5 emission standard.

In 1961, the Soviet research organization of
NATI, NAMI and VNIImotoprom started experimental development, and created
experimental engines with different technologies.

Soviet automobile manufacturer AvtoVAZ also
experimented with the use of Wankel engines in cars but without the benefit of
a license. In 1974 they created a special engine design bureau, which in 1978
designed an engine designated as VAZ-311. In 1980, the company started delivering
Wankel-powered VAZ-2106s (VAZ-411 engine with two-rotors) and Ladas, mostly to
security services, of which about 200 were made. The next models were the
VAZ-4132 and VAZ-415. Aviadvigatel, the Soviet aircraft engine design bureau,
is known to have produced Wankel engines with electronic injection for aircraft
and helicopters, though little specific information has surfaced. 

Although many manufacturers licensed the
design, including Citroën with their M35 and GS Birotor, using engines produced
by Comotor, General Motors, which seems to have concluded that the Wankel
engine was slightly more expensive to build than an equivalent reciprocating
engine, although claiming having solved the fuel economy issue, but failed in
obtaining acceptable exhaust emissions, and Mercedes-Benz which used it for
their C111 concept car, only Mazda has produced Wankel engines in large
numbers. American Motors (AMC) was so convinced “…that the rotary engine will
play an important role as a powerplant for cars and trucks of the future…”,
according to Chairman Roy D. Chapin Jr., that the smallest U.S. automaker
signed an agreement in February 1973, after a year’s negotiations, to build
Wankels for both passenger cars and Jeeps, as well as the right to sell any
rotary engines it produces to other companies. The automaker’s President,
William Luneburg, did not expect dramatic development through 1980, but Gerald
C. Meyers, AMC’s Vice-President of the Product (Engineering) Group, suggested
that AMC would be buying the engines from Curtis-Wright before developing its
own Wankel engines and predicted a total transition to rotary power by 1984.
Plans called for the engine to be used in the AMC Gremlin, but development was
pushed back. American Motors designed the unique Pacer around the engine, even
though by 1974, AMC had decided to buy the Wankel engines from GM instead of
building them itself. However, GM’s engines had not reached production when the
Pacer was to hit the showrooms. Part of the demise of this feature was the 1973
oil crisis with rising fuel prices, and also concerns about proposed US
emission standards legislation.

General Motors did not succeed in having a
Wankel engine meeting both the emission requirements and having good fuel
economy, so in 1974 the company canceled its development, although GM claimed
having solved the fuel economy problem and having obtained engines with a
duration above 530,000 miles; unfortunately they just published a few papers on
the results of their research. This meant the Pacer had to be reconfigured to
house AMC’s venerable AMC Straight-6 engine with rear-wheel drive.


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 a housing. The expansion phase of the Wankel cycle is much longer
than that of the Otto cycle. In the basic single-rotor Wankel engine, the
oval-like epitrochoid-shaped housing surrounds a rotor which is triangular with
bow-shaped flanks (often confused with a Reuleaux triangle, a three-pointed
curve of constant width, but with the bulge in the middle of each side a bit
more flattened).

The theoretical shape of the rotor between
the fixed corners is the result of a minimization of the volume of the
geometric combustion chamber and a maximization of the compression ratio,
respectively. The symmetric curve connecting two arbitrary apexes of the rotor
is maximized in the direction of the inner housing shape with the constraint
that it not touch the housing at any angle of rotation (an arc is not a
solution of this optimization problem). 

The central drive shaft, called the eccentric
shaft or E-shaft, passes through the center of the rotor and is supported by
fixed bearings. The rotors ride on eccentrics (analogous to cranks) integral to
the eccentric shaft (analogous to a crankshaft). The rotors both rotate around
the eccentrics and make orbital revolutions around the eccentric shaft. Seals
at the corners of the rotor seal against the periphery of the housing, dividing
it into three moving combustion chambers. The rotation of each rotor on its own
axis is caused and controlled by a pair of synchronizing gears. A fixed gear
mounted on one side of the rotor housing engages a ring gear attached to the
rotor and ensures the rotor moves exactly 1/3 turn for each turn of the
eccentric shaft. The power output of the engine is not transmitted through the
synchronizing gears. The force of gas pressure on the rotor (to a first
approximation) goes directly to the center of the eccentric, part of the output

The best way to visualize the action of the
engine in the animation at left is to look not at the rotor itself, but the
cavity created between it and the housing. The Wankel engine is actually a
variable-volume progressing-cavity system. Thus there are 3 cavities per
housing, all repeating the same cycle. Note as well that points A and B on the
rotor and e-shaft turn at different speed, point B moves 3 times faster than
point A, so that one full orbit of the rotor equates to 3 turns of the e-shaft.

As the rotor rotates and orbitally revolves,
each side of the rotor is brought closer to and then away from the wall of the
housing, compressing and expanding the combustion chamber like the strokes of a
piston in a reciprocating engine. The power vector of the combustion stage goes
through the center of the offset lobe.

While a four-stroke piston engine makes one
combustion stroke per cylinder for every two rotations of the crankshaft (that
is, one-half power stroke per crankshaft rotation per cylinder), each
combustion chamber in the Wankel generates one combustion stroke per driveshaft
rotation, i.e. one power stroke per rotor orbital revolution and three power
strokes per rotor rotation. Thus, power output of a Wankel engine is generally
higher than that of a four-stroke piston engine of similar engine displacement
in a similar state of tune; and higher than that of a four-stroke piston engine
of similar physical dimensions and weight.

Wankel engines also generally have a much
higher redline than a reciprocating engine of similar power output. This is in
part because the smoothness inherent in circular motion, but especially because
they do not have highly stressed parts such as a crankshaft or connecting rods.
Eccentric shafts do not have the stress-raising internal corners of
crankshafts. The redline of a rotary engine is limited by wear of the
synchronizing gears. Hardened steel gears are used for extended operation above
7000 or 8000 rpm. Mazda Wankel engines in auto racing are operated above 10,000
rpm. In aircraft they are used conservatively, up to 6500 or 7500 rpm. However,
as gas pressure participates in seal efficiency, running a Wankel engine at
high rpm under no load conditions can destroy the engine.

National agencies that tax automobiles
according to displacement and regulatory bodies in automobile racing variously
consider the Wankel engine to be equivalent to a four-stroke engine of 1.5 to 2
times the displacement; some racing series ban it altogether.


Felix Wankel managed to overcome most of the
problems that made previous rotary engines fail by developing a configuration
with vane seals that had a tip radius equal to the amount of “oversize” of the
rotor housing form, as compared to the theoretical epitrochoid, to minimize
radial apex seal motion plus introducing a cylindrical gas-loaded apex pin
which abutted all sealing elements to seal around the 3 planes at each rotor

Rotary engines have a thermodynamic problem
not found in reciprocating four-stroke engines in that their “cylinder block”
operates at steady state, with intake, compression, combustion, and exhaust
occurring at fixed housing locations for all “cylinders”. In contrast,
reciprocating engines perform these four strokes in one chamber, so that extremes
of “freezing” intake and “flaming” exhaust are averaged and shielded by a
boundary layer from overheating working parts. 

The boundary layer shields and the oil film
act as thermal insulation, leading to a low temperature of the lubricating film
(max. ~200 °C/400 °F) on a water-cooled Wankel engine. This gives a more
constant surface temperature. The temperature around the spark plug is about
the same as the temperature in the combustion chamber of a reciprocating
engine. With circumferential or axial flow cooling, the temperature difference
remains tolerable.

Four-stroke reciprocating engines are less
suitable for hydrogen. The hydrogen can misfire on hot parts like the exhaust
valve and spark plugs. Another problem concerns the hydrogenate attack on the
lubricating film in reciprocating engines. In a Wankel engine, this problem is
circumvented by using a ceramic apex seal against a ceramic surface: there is
no oil film to suffer hydrogenate attack. The piston shell must be lubricated
and cooled with oil. This substantially increases the lubricating oil
consumption in a four-stroke hydrogen engine.


Unlike a piston engine, where the cylinder is
cooled by the incoming charge after being heated by combustion, Wankel rotor
housings are constantly heated on one side and cooled on the other, leading to
high local temperatures and unequal thermal expansion. While this places high
demands on the materials used, the simplicity of the Wankel makes it easier to
use alternative materials like exotic alloys and ceramics. With water cooling
in a radial or axial flow direction, with the hot water from the hot bow
heating the cold bow, the thermal expansion remains tolerable.


Early engine designs had a high incidence of
sealing loss, both between the rotor and the housing and also between the
various pieces making up the housing. Also, in earlier model Wankel engines
carbon particles could become trapped between the seal and the casing, jamming
the engine and requiring a partial rebuild. It was common for very early Mazda
engines to require rebuilding after 50,000 miles (80,000 km). Further sealing
problems arise from the uneven thermal distribution within the housings causing
distortion and loss of sealing and compression. This thermal distortion also
causes uneven wear between the apex seal and the rotor housing, quite evident
on higher mileage engines. The problem is exacerbated when the engine is
stressed before reaching operating temperature. However, Mazda Wankel engines
have solved these problems. Current engines have nearly 100 seal-related parts.

The problem of clearance for hot rotor apexes
passing between the axially closer side housings in the cooler intake lobe
areas was dealt with by using an axial rotor pilot, radially inboard of the oils
seals plus improved inertia oil cooling of the rotor interior ( C-W patents
3,261,542, C. Jones, 5/8/63, 3,176,915, M. Bentele, C.Jones. A.H. Raye.
7/2/62), and slightly “crowned” apex seals (Different height in the center and
in the extremes of seal).

Motorcycle Engines:

The world’s first Wankel-engined motorcycle
was the 1960 IFA/MZ ‘KKM 175W’ built by German motorcycle manufacturer MZ on a
licence from NSU. 

In 1972, Yamaha introduced the ‘RZ201′ at the
Tokyo Motor Show, a prototype with Wankel engine, weighing 220 kg and producing
60 hp from a 660 cc engine. 

From 1974 to 1977 Hercules produced a limited
number of motorcycles powered by Wankel engines. 

The Suzuki RE5 single-rotor motorcycle was
produced from 1975 to 1976. It proved to be a complex design, with liquid
cooling and oil cooling, and multiple lubrication and carburation systems. It
worked well and was smooth, but being rather heavy and having a modest 62 bhp
power output, it did not sell well.

Dutch motorcycle importer and manufacturer
van Veen produced small quantities of their dual rotor Wankel-engined OCR-1000
between 1978 and 1980, using surplus Comotor engines. 

In the early 1980s, David Garside’s BSA
twin-rotor engine reached production at Norton as the air-cooled twin-rotor
Norton Classic. The Classic was succeeded by the later liquid-cooled Norton
Commander and the Interpol2, a police version. (These machines used motor
tooling and blank apex seals). The Norton engine later formed the basis for the
MidWest AE series aero-engine. Norton used a Wankel engine in several models
including the Norton F1, F1 Sports, RC588, RCW588, NRS588, most notably Steve
Hislop riding to various victories on Norton’s F1 in the TT in 1992.

Norton has proposed a new 588 cc twin-rotor
model called the NRV588 and a 700 cc version called the NRV700. A former
mechanic at Norton moved to Australia, and founded there a rotary engined
motorcycles producer named Roton, whose products won several local races.

No motorcycles with Wankel engines have been
produced for sale to the general public for road use since 1992. 

to Rotary Power Crew for the preceding information….





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