design concept sketch of the Spagthorpe Basenji without bodywork.
The conventional dual-reverse Earles fork is plainly visible. Note
how the “upside-down” engine mounting creates the classic
side-by-side intake and exhaust runners.
Review by Wolfgang
Ahh, the Basenji.
I found one in a junkyard in Seattle last summer on my way back from the
Wet Blanket Run and Swamp Meet. Its engine layout is in the best Spagthorpe
tradition. Superficially resembling a six-cylinder radial engine with
the transmission connected in the wrong place, its power plant is actually
a transversely-mounted counter-rotating dual-rotor Wankel. The two counter-rotating
rotors are connected through crown gears on their eccentrics and coupled
by six bevel gears. These gears drive six radially mounted “accessories”
to the engine:
||Since the primary shaft is centrally mounted, the transmission employs
a unique system of matched counter-rotating twin secondary shafts
and driveshafts, which double as the rear trailing links.
||in the oil sump (interchangeable with the immersed water pump)
||in the water sump (interchangeable with the immersed oil pump)
||mounted in front of the radiator, which had a hole in it to accommodate
||Its position is the reason the radiator fan is in front of the radiator;
it required the radiator to have a special sort of notch in its top.
||Since it ran at six times the engine speed, and a reduction gearset
would have introduced unacceptable complications to the n-rotating-mass
calculations, not to mention delays in the design schedule, a special
and difficult-to-find divide-by-four electronic module was fitted.
Most of these have been removed from Basenjis and fitted to Intel
CPUs to make them more reliable.
Carburetion is provided
by two pairs of four-way bilaterally symmetric side-draft carburettors
mounted on the sides of the rotors. As the Wankel engine is mounted “upside-down",
the carburettors are at the bottom, occupying the position normally reserved
for the cylinder heads in boxer twins. They are fed by ram-air pipes that
lead upwards and diagonally forwards, next to the parallel exhaust tubes,
which lead down from the top of the engine case.
The whole complicated
mess was designed in an effort to overcome the legendary difficulties
that traditional single-shaft motorcycles encounter while trying to wheelie
or countersteer. According to the common wisdom, coriolis forces caused
by the rotating mass of the driveshaft cause the motorcycle to fall over
sideways when wheelying and prevent the bike from leaning in a turn.
It was the intent
of Spagthorpe engineers to divide the rotating masses of the engine and
drivetrain in to a number of perfectly matched and balanced pairs:
- twin-Wankel rotors
- clutch and transmission
primary shaft and radiator fan
- dual transmission
- oil pump and alternator
- water pump and
During the assembly
process, assemblies of counterrotating items are meticulously selected
to precisely match their polar moments of inertia. Early production runs
attempted to precisely match the immersed fluid pumps to each other as
well as to their counterrotating pairs, but this bit of design ingenuity
was dropped in later production runs because of the expense involved.
Warning: If the serial number of your Basenji is greater than 12, do not,
under any circumstances, swap the oil and water pumps. Through originally
specified to be interchangeable, the resulting mismatch of four counterrotating
masses could result in unpredictable results.
As a result of all
these counterrotating masses, the Basenji is directionally stable in the
extreme. However, because of the great bulk of the engine, the fuel tank,
which in any true motorcycle can only occupy the space above the engine,
has a capacity of about half a gallon, which the Basenji consumes in about
ten miles. As luck would have it, the Basenji is easier to steer toward
a filling station with the engine off.
accomplished countersteerer, canyon-blaster, and test pilot, discovered
one other dangerous side effect of this engine design. When a single rotating
mass is perturbed, it generates a force at a right angle to the perturbing
force. The results of such an action are easily predicted by ordinary
Newtonian physics. These well-understood effects are the basis of modern
systems in guided-missile missile guidance systems. However, the Basenji
engine’s rotational characteristics are not those of a simple rotating
mass. There are six pairs of counterrotating masses in four alignments
create intolerable perturbations whose resulting force cannot be at right
angles to any of the orginal dimensions. That force is expressed in another,
hidden dimension, and causes the motorcyle and its rider to be pushed
into parallel universes. Nigel failed to return from a test run one day
and wasn't seen for many months. His adventures, tamed down for the teenager
set and modified to disguise the true nature of the alternate-universe
vechicle, were weakly documented in the television series “Sliders.”
armed with an Infernosoft Difference Engine, were able to deduce his fate.
As a result, service bulletins were issued to both dealers. Certain parts
of Basenjis, as they were brought in for the 100-, 200-, 300-, 500-, 800-,
1300-, 2100-, and 3400- mile services, were to be modified in ways still
not entirely clear. Without risking deliberately inducing the dimension-sliding
effect, it is difficult to tell whether a Basenji has been so modified.
Upon closer examination
of my new Basenji, I discovered some rather odd things about it. Its license
plate, VIN tag, and federal safety warning stickers do not contain the
letter J. Neither does the model marquee: it says “Basengi.”
Where have you been, my friend? Do I dare replace your electronic ignition
module and take you for a spin?
A concept sketch of the Spagthorpe Basenji frame. This view shows
the core of the dual-rotor Wankel engine surrounded by its six
counterrotating acessories. Note the cooling fan in front of the
radiator. This is obviously an early design of the Basenji I:
its rear suspension is the original dual-driveshaft/trailing link
Spagthorpe Technical Liason
I, 1988–1993: live-shaft trailing links rear, conventional double-inverse
Earles fork front. The rider directly sets the steering angle through
a deceptively simple direct mechanical linkage.
Basenji II, 1994–1998:
double-inverse Earles rear suspension; hydraulically actuated hub-steered
double-inverse Earles fork front. In this remarkable revolutionary deign,
there are no conventional sliding-tube forks. Instead, the handlebars
simply pivot in their pwn special mount and are connected to a double-action
hydraulic piston acting as a master cylinder. Moving the handlebars pushes
hydraulic fluid through flexible hoses to the hub-steering system, in
which slave cyliders adjust the position of the suspension carriers.
Basenji III, 1999–:
power hydraulic Hub-steering. In a natural evolution of the Series II’s
revolutionary steering concept, the handlebars are connected to double-action
hydraulic valves. These valves admit more or less hydraulic fluid into
the flexible hoses. The system acts as an amplifier of the rider’s
effort, whcih is thus significantly reduced. The Series III has introduced
a radical new concept in motorcycle steering mechanisms. The hydraulic
valves, instead of directly actuating the hub-steering, actuate the rate
of steering change. Thus to enter a turn, only a momentary nudge of the
appropriate steering bar is required. To exit the turn and return to straight-ahead
motoring, a momentary nudge in the other direction is required.
Spagthorpe Technical Liason
not replace dual-valve tubes with single-valve tubes. The Basenji’s
dual-valve system of inner tubes ensures that this annoying source
of tyre imbalance is eliminated. Using a conventional single-nipple
inner tube is not warranted.
valve cores and valve covers on dual-valve tubes, ensure that the
correct thread-handedness is observed.
tubes with the same thread on both valves, whether left- or right-handed,
tubes with dual-thread components are counterfeit. Spagthorpe Engineering
considered using our patented dual-thread technology for this application,
but confusion about which nipple was right-handed and which nipple
was left-handed led to problems with cross-threading.
replacing the components of the double-inverse Earles suspensions,
ensure that a) you have built a symmetrical suspension and b) that
the suspension is properly oriented to maintain the motorcycle’s
anti-dive characteristics. Reversing the suspension setup could result
in surprising behavior under braking.
rebuilding the double-inverse Earles suspensions, mark each component
with painted dots of the following color combinations: All left-hand
components should be in shades of green; all right-hand components
should be in shades of red. Starting from the frontmost components,
begin with the brightest shade of red or green; as you move back,
use steadily darker components.
with the next model year, Basenji suspension components will be marked
with factory-standard colored dots to aid in suspension reassembly.
Careful consideration was made of nautical conventions and the prevalence
of red-green color blindness in Spagthorpe customers. (All assembly
dots are now pale blue.)
hydraulic lines of the hub-steering must be kept free of contamination.
Air in the system could result in sluggish steering response. Water
in the system could freeze, resulting in suboptimal steering system
replacing any of the oil pump, water pump, alternator, or distributor
in the Basenji, you must replace all four components as a matched
set. Mass-balancing is vital to the correct operation of this motorcycle.
oil pump and water pump of the Series II Basenji are no longer interchangeable.
Increased labor costs resulting from the need to precisely match the
rotating mass of four components led to this unfortunate assault on
the design purity of the Series I. However, matched water pump/distributor
or oil-pump/alternator pairs are now separately interchangeable between
Series I and II machines.
oil pump and alternator of the Series III Basenji are not interchangeable
with components from the Series I or II. The power-hydraulic hub-steering
system puts an extra load on the oil pump, which thus had to be upgraded
for Series III. The alternator, likewise, was upgraded to match the
oil pump’s increased rotating mass.
upgrading from a Series I to a Series II, be aware of the changes
in the motorcycle’s handling characteristics. To help familiarize
new riders with the Series II’s handling characteristics, the
Series II’s purchase price includes a two-week stay at the Scroddham-Scratche
Proving Grounds for rider training. Previous owners of Spagthorpe
Motorcycles who opt to purchase an Basenji Series II are invited to
stay at the luxurious Bedlam Hilton for daily group therapy sessions
and relaxing electroshock therapy.
riders of the Series III Basenji are reminded that centering the steering
requires an opposite push on the handlebars, not an upward push on
the right handlebar.
neutral-steer indicator light system is available as a mandatory retrofit
for all Series III Basenji motorcycles.
installing the neutral-steer indicator light system, you must ensure
that the symmetrical wiring harness is correctly installed. Reversing
the harness could result in unknown side effects.
Note #987 is invalid. Since the wiring harness is symmetrical, it
doesn't matter which way you install it.
neutral-steer indicator light system installed in a previous mandatory
retrofit is the subject of a mandatory retrofit. The green light used
in the original mandatory retrofit are too easily confused with the
green light indicating that the transmission is in neutral. Since
red was not available (it indicates a problem with the oil pump, water
pump, or alternator), amber was not available (it indicates low oil,
water, or fuel), green was not available (it indicates a turn signal),
and blue was not available (it indicates high beam or Cherenkov radiation),
a unique pattern was devised: A twin-color LED is now used. In conjunction
with the distributor’s divide-by-four circuitry, a repeating
pattern of yellow - red - yellow - green indicates that the steering
is centered. (Alternating red and geen indicates left of center and
alternating green and red indicates right of center.)
I, II, III
installation of asymmetric-pattern headlights is not recommended,
as these could upset the motorcyle’s sensitive balance.
I, II, III
sidestand retrofits are mandatory for all Basenji motorcycles. A problem
in early production-run Basenji motorycles was traced to mass-asymetries
resulting from having a sidestand only on one side of the motorcycle.
All Basenji motocycle owners are requested to return their motorcycles
to either of the Spagthorpe dealers for immediate fitment of the second
sidestand. Since Basenjis made for the American market have sidestands
on the opposite side as those made for the Japanese/English market,
we assure our customers that both types of sidestands are readily
I, II, III
for the left and right rotors, though fitted with identical (non-symmetrical)
mating surfaces and functionally identical, are not interchangeable
after the motorcycle has logged 3682 or more miles of service (2876
miles under high-speed conditions). Apparently the symmetries of intake
airflow through the induction system cause uneven but symmetrical
wear on the carburettors' inner surfaces.