Cycle News - Archive Issues - 1980's

test track in July, Le Rou x established a full -time racing department with test rider Malcolm Heath as th e th ird man, with th e aim of running a prototype machine in th e last few races of the '87 Bri tish season so as to iron out devel op m ent bu gs before going racing at international level next year with at leas t a two- man tea m, rising to four riders for the Isle of Man Senior "IT which will be the fir m's principal target. That's if they . don't go GP racing . . . Do n ' t laugh ! Don't even smile at the idea of a Norton rotary racer lin ing u p wi th the current breed o f sta te of th e a rt two- strokes for a World Championship G P in th e nex t year or so, because if you do you'll live to regret it. Natural cynics as so many of us have become - and none more ' so than the British motorcycle press - at news of yet another " G rea t British World-Beater," this time I assure you , you must take it serious ly. . I' ll admi t I was skeptical about the bike's potential when I turned u p to ride it a t Mallory; a ll th ose reports I'd hea rd ab o ut 135 bh p fro m a n engine which, shorn of its massive cooling fins, is no bigger than a shoe box, coupled to a dry weight of 286 pounds seemed like typical GB WB overstatement, Bu t it isn 't. The fact of the matter is that the RC588 Norton rotary already has a level of performance on a par with a well-tuned RS500 Honda th reecylinder G P bike in terms of acceleration and top speed - those power to weight figures are real enough but WIth one im portant difference: whereas th e reed- val ve Honda two stroke, mainstay of th e 500cc G P class, has a power band of about 3500 rpm , the Norton's is practically infinite. It doesn 't just pull from nowhere - it pulls from anywhere! Allow the revs to die away, which they'll do very quickly thanks to the minimal inertia effect and practically non-existent internal friction of the air-cooled twin-rotor engine, such as for example when yo u exit Mallory's infamous chicane, and by cracking open the throttle at 3000 rpm in seco nd gear yo u ' ll be rewarded not by a co ugh or a hiccup or' a re lucta nce to s tart p ull ing properly before the cams or th e p ort timmg start to work properly, b ut by a liquid-smooth rush of usable power which continues uninterruptedly in lineally-increasing fashion up to the nominal red line of 9000 rpm. Nominal, because Crighton has been working on race engine development for the lengthy period of just six weeks, and is not yet sure of the effects of continued high revs such as the 14,000 rpm of which the engine unit is ca pable on component life. "With such a wide spread o f power The rotary racing project is the brainchild of Brian Crighton. The two-into-one exhaust system feeds into an absorption silencer mounted under the engine and then into an exhaust ejector. Cathcart rode the Norton Rotary Road Racer at England's Mallory Park and compared its performance to that of a Honda RS500 GP b ike. there isn't much point in revving it so h igh ," he say s, "but we'll know more once we can start testing the en gin e on our new ' dyno which arrived this week. The old one would onl y tak e up to 125 bhp a nd the engine's too powerful for it a lrea dy. We keep taking th e engine apart to measure wear, but there hasn 't been' any so far. " Sounds like a marked contrast to the need to rebuild and rep la ce components inside racing two-stroke engines producing the same sort of horsepower; co u ld th e rotary engine be th e answer to the rising cos t of go in g GP racing? . Beca use th e racing project is in its infancy, the R C588 's engine is remarkably close to the 80 bhp police . bike power unit in terms o f specification :- and to the 90 bhp aircooled motor which will power the Norton Classic, the first civilian rotary-engined model which was la u n ch ed at the Birm in gh a m (En gland) Show in early October. All major engine ca sti n g s are' standard, as are the steel rotors and five-speed gearbox with oil-bath . multiplate cl utch and d uplex chain primary drive. Crighton dismisses his own tu n in g efforts as simply playing abou t with the port shapes and timi ng , as well as slightly altering th e combustion chambers, bu t there's obviously more to extracting a 50% power increase and the sort of performance th e bike is capable of than these tried and true techniques of the two-stroke tuning manual which are of eq ual va lidity in the realms of rotary engine develop men t. One of the key tricks up his sleeve is th e induction len g th of the long, curved tu bes on which th e twin 34mm Amal smoothbore carburetors are mounted, and another is th e fac t that these face forwards for a ram air ' effect, fed by two vents in the leading edges of the fairi ng and of proven validity: th e police bikes on th e o ther hand have rear-mounted carbs which draw air that has already passed th rough the deep finning on the rotor housin~ to cool th e rotors. That's fine with "3 90 bhp road bike but it impedes th e flow on a h ig hperformance engine, so what Crighton has don e is to use a venturi effect on the exhaust system to create a negative pressure w hich, coupled with the forward spe ed of the bike which creates a positive pressure, pu ts a n imbalance on th e engine so that air rush es through th e center of it to actually cool it. This enables the intake system to be directed completely into atmosphere, resulting m a substantial power increase. Those long induction tubes are designed for the correct resonant length at 9000 rpm; because the induction phase is so long - more than a single tu rn of the eccentric shaft which is the eq uivalent of a crankshaft in a co nventional en gine - it's desirable to h ave in d uction tracts th is lo n g in order to get th e wave action of the charge timed correctl y. The exhaust is a two-into-one system feeding into an absorption silencer mounted under th e engine, whi ch in turn feeds into what Crighton terms an exhaust ejector, that actually provides the negative pressure for the coo lin g. Incorporated in th is is an extremely clever wh eeze, whereby oil from a tank located in the seat is injected into the main bearin gs on the en d of the ecce ntric shaft, after w h ic h t he airflow th rough the engine actually draws the oil through and .sp lash es it everyw he re ins ide, after that, it's drawn out down the large-di ameter pipe with flexibl e coupling attached to th e exhaust system , into which it's vented. Because the engine runs very hot - about lOoo°C is normal for th e ex haust gas temperatures - the exha ust is in stainless steel , into which the waste oi l flows and then immediately vaporizes: because it's so hot, the engine doesn 't smoke . l-< C1) ..0 8 C1) ;> o Z The twin spar aluminum chassis was fabricated by Spondon. Norton Rotary RC588 Engine Twin rotor air-cooled rotary Dimensions 2x294cc swept volume t roch oidal chambers Capacity See text: currently rated at 1176cc by ACU Output .. • . 135 bhp at 9,500 rpm (at eccentric shaft) Compression ratio 9 .2 :1 Carburetion 2x34mm Amal smoothbore Ignit ion Norton hall-effect triggered COl Gearbox 5-speed constant mesh with duplex chain primary Clutch .... 20-plate oil-bath multiplate with siritered bronze frictio n plates and diaphragm spring Chassis . .... Fabricated aluminum twin spar Front: 40mm Suspension Kayaba telescopic forks w ith rising-rate monoshock and Ohlins gas unit Wheelbase 141 Omm Brakes Front: 2x310mm Spondon discs with four-p iston . Spondon calipers Rear: 1x220mm Spondon disc with two-piston Brembo cliper Whee ls/tires ..... Front: 12/60 . 17 Michelin on 3 .5 in. Dymag . Rear: 18/67 - 17 Michelin on 5 .5 in . Dymag Weight 286Ibs. 19

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