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Basenji

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    An early 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 Spachdorf

    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:

    Engine Accessory Purpose
    Transmission 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.
    Oil Pump in the oil sump (interchangeable with the immersed water pump)
    Water Pump in the water sump (interchangeable with the immersed oil pump)
    Radiator Fan mounted in front of the radiator, which had a hole in it to accommodate the shaft
    Alternator 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.
    Distributor 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 secondaries
    • driveshafts
    • oil pump and alternator
    • water pump and distributor

    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.

    Nigel Spagthorpe-Whitworth, 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.”

    Spagthorpe engineers, 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 system.

     


    Basenji Suspension Design History

    Wendell Gunderson-Ogelthorpe, Spagthorpe Technical Liason

    Basenji Series 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.


    Basenji Technical Bulletins

    Wendell Gunderson-Ogelthorpe, Spagthorpe Technical Liason

     
    Number Date Models Affected Details
    1 January, 1989 Basenji Do 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.
    2 January, 1989 Basenji

    When replacing valve cores and valve covers on dual-valve tubes, ensure that the correct thread-handedness is observed.

    3 March, 1992 Basenji Inner tubes with the same thread on both valves, whether left- or right-handed, are counterfeit!
    5 April, 1993 Basenji Inner 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.
    8 April, 1996 Basenji II When 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.
    13 July, 1996 Basenji II Before 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.
    21 September, 1996 Basenji II Beginning 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.)
    34 March, 1997 Basenji II The 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 stability.
    55 June, 1997 Basenji II When 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.
    89 August, 1997 Basenji II The 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.
    144 March, 1999 Basenji III The 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.
    233 March, 1999 Basenji II When 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.
    377 June, 1999 Basenji III BMW 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.
    610 September, 1999 Basenji III A neutral-steer indicator light system is available as a mandatory retrofit for all Series III Basenji motorcycles.
    987 October, 1999 Basenji III When 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.
    1597 January, 2000 Basenji III Technical Note #987 is invalid. Since the wiring harness is symmetrical, it doesn't matter which way you install it.
    2584 August, 2000 Basenji III The 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.)
    4181 August, 2000 Basenji I, II, III The installation of asymmetric-pattern headlights is not recommended, as these could upset the motorcyle’s sensitive balance.
    6765 September, 2000 Basenji I, II, III Symmetrical 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 available.
    10,946 November, 2000 Basenji I, II, III Carburettors 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.

     

    Spagthorpe Home Wolfgang Spachdorf and Wendel Gunderson-Ogelthorpe
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