Cycle News - Archive Issues - 1980's

The OW81 engine is nestled in a t win -sp ar alumin um fra me and f eatures re ed-valve ind uc tion. (Above) Peter C lifford puts t he Sonato /Gauloises OW8 1 Yamaha through its paces at Paul Ricard in the south of France. (Below) Th e OW81 t hat Christian Sarron took to third place in the 500cc World Cha m pionship . Ch r i s t i a " Sarr o ,,'s OWBl Yamaha test By Peter Clifford That unmistakable, horrendous scraping of m etal and fiberglass on tarmac accompanied the 500cc Yamaha as it slid across the Pau l Ricard circuit at 100 mph . The bike cam e to rest a sorry sig ht, lying o n i ts side in th e slo wly sett li ng dust. Fortunately, it was no t th e genuine Christian Sarron Ger- 14 man Grand Prix-winningOW81 that ha d fallen but rat her an RD 500 Sarro n Rep lica roa d bik e. But it st ill served as a reminder o f h ow eas ily mista kes ca n be made. T h e OW81 it self wa s certa in ly not a mach in e LO tak e li berties wi th . As you would suspe ct, a mach in e that carried Sarron LO o ne gr a nd p rix win a n d Edd ie Lawson LO three ha s so much power that it p u ts a ll ot hers excep t Fred d ie Spe n cer's N SR500 H onda to sha me. Comparin g it with m y recent experience o n th e works Suzukis o f McElnea a nd Unci ni , it is in a different class. Even agains t th e NS500 Honda I rode last yea r, th e Yamaha had marginally more grunt. In truth, I would be lying if I suggested that it wa s possible LO feel an y small num erica l peak pow er advantag e that the Ya ma ha has, bu t the dif ference in m idrange power is there. The Yam a ha is very strong fro m low down, yet th ere is sti ll a very not icea ble kick between 8000 a nd 8500 rpm . At fir st, th is m a kes th e bike ha rsh to rid e, but it is surprisi ngly easy to keep th e en gin e runn in g between 9000 a nd I 1,000 rpm , h elp ed by a very clos e-ra tio gea rbox used for the short- ' ened Ricard circu it. Th e V-Iour has a bore a nd stro ke of 56 by 50.6mm a nd dra ws air a nd fuel through two twin -cho ke, fla t-slide Mikuni carbs, gi ving four ventu ri o f either 34 or 35mm diameter depending on th e circu it. The induct ion is dire ct into th e cra n kcases th ro ug h fou r sets of reed valves , a n d th e two pressed cra n ks have four roller bearings eac h . T h e cylin ders h ave five transfer ports an d new for th is yea r were th e boost ports eith er side o f th e m a in exha us t port s. The g u illoti ne valve varies the port h eigh t LO give th e engine flexibi li ty. but the su dde n openi ng o f the gu illotine h elps p roduce th e po wer surge between 8000 a n d 9500 rpm. Sarron wa nts the factory LO develo p a m ore grad ua lly o pe n ing va lve by develo pin g the electron ics that co n tro l th e electric mot or. The en gine was o n ly part o f th e impressive packa ge offered by th e 190-mph moto rcyc le, It had th e m ost ne utral steeri n g feel o f a ny m ach in e I have ridden . It had th at perfect bal ance of n o-effo rt steer ing withou t fall in g into co rners lik e so man y racers seem LO do befo re yo u get used LO th em a nd rid e har der . T h e Yamaha ha s no t rea ch ed thi s point of steering perfectio n by cha nce. I rod e th e ea rl ier, 1983 di sc-val ve Vfour. a nd th at wa s a bit o f a monstrosity by co m pariso n, a real pai n to cha n ge di rect ion from left LO right. sta ble through fast co rners bu t very h eavy. The 1985 version seemed no less sta ble. but wa s as ligh t as yo u co u ld wish fo r fro m a 500cc. Its o n ly slig h t m inus wa s a percep tible ten de ncy to sta nd up whil e bra ki ng in to a corner . bu t th e Yamaha was nowhere near as bad as U nci n i's a lu m in u mframed Suzuki in th is respect. Lik e th e Suzu ki, th e h ead an gle ca n be a lte red a nd o n the Yamaha this is accom p lished by cha ngin g th e LOp and bo ttom bearing holders in the generous steeri ng-head section. The Fren ch sq ua d steepened the steering head for circu its like LeMa ns and Assen wh ere Sarron th ough t th at h e needed th e bi ke to steer in quicker a nd did not m in d a slig h t lessen ing of h igh-speed sta bil ity. The team p referred to cha nge the head angle ra th er tha n a lte r th e off set in th e triple clamps and h ence the trail. Even Sa rron, ridi ng hi s machine a few light-years faster th an I, had li tt le LO co m p la in abo ut. " I have as ked th at for n ext year th ey mak e th e power more progr essive between 8000 and 8500 because. unl ike Eddie Lawso n, I so metimes like LO use this power in th e mi ddle of th e co rn er. We also n eed a li tt le more topend po wer beca use th e four-cylin der H onda h as a slig h t edge. We h ave bett er accelera tio n tha n th e three-cylinder H onda s even if th ere is n o t tha t much d ifference in th e to p spe ed. Wh ere th e threes do seem to ha ve an advant age is th at th ey are eas ier LO get th rough the co rn ers - they have slig h tly less power , so th ey are easier to ride." An other improv ement Sa rro n would like to see ha s more LO do with hi s sta tu re than th e bike as he wants a sma ller, shorte r tank th at will all o w \ him to ge t h is slig h t weig h t furt her over th e fro n t wh eel a nd keep it on th e grou nd more. Even with m y h eavi er bu ild, th e Yamaha was keen to wh eeli e though I was ca ut io us en ough LO keep a ny fro nt-wheel rising low , a n d well in co nt ro l. I needed a ll th e steering co ntrol avai la ble; the Yamaha lunged tow ards the next corne r so fast th at stra igh ts shrun k into bo u ts o f gea r cha ngin g lead in g a lmost in stantly LOa firm grab for th e fro nt brake. T hi s ca lle d on th e twi n Brernbo-Iour-piston ca lipers to impi nge u pon the 12.6-inch steel ro to rs a nd h au l down th e Yamaha with a su perb bal ance o f effort less power a nd co n fide nce-inspiri ng feel. Natura llv, th e non-ant i-dive forks su n k rapid ly as all th e weig ht went o nto th em bu t wi th out crea ting th e feeli ng th a t th e bike wa s runn in g o n its n ose. Earlier 500cc Yamaha s ha ve had a ntidive systems, bu t th ey spe nt a lmost a ll th eir time adj usted LO zero an d th e factory ha s no w co nce ntra ted on irnprovin g th e sp ringing a nd damping co n tro l in th e fo rks, whi ch is o ften upset by damping-restri ctive a ntidive systems . T h e O W81 Yamaha fork s have separat e adj us tme n t for co mpression a nd rebo u nd dampin g . The cornp ression is adjus ted by turni n g a kn ob o n th e back o f th e low er fo rk leg to one o f th e I I positions. Th e re bo u nd is a lte red by a kn ob o n th e to p o f th e for k, with 10 positio ns. Th ere are two for k sp rings withi n the legs a nd the p reload ca n be adj usted but th e tea m does no t varv the am ount o f fo rk o il. The rear suspension is ca red for by a single Oh lins shock using coil spring and Ni trogen to look a fter th e sp ringin g a nd a knob o n th e LOp of th e left fork leg allow s th e rider LO adjust th e sp ring p reload in mi d fligh t. These special un its ar e expensive a n d whi le La wso n had h is in 1984. Sarro n and Roche on ly acquired simi lar versions a t th e Belgian Grand Prix this yea r , halfway th rough th e season. La wso n uses his n o t o n ly LO set th e bik e up d uri ng practice bu t to co mpensate durin g th e race. As th e fue l gets used up, h e ca n ba ck 'o ff th e p reload for th e ligh ter bike a nd if th e tire sta rts LO go a way , he can mak e life easier by so fteni ng th e suspens io n 'a fra cti on . T he top of th e sus pe nsion unit is ' mounted in th e frame, forw ard o f th e seat, and the ride height can be a ltered by win di ng th e mounting up a nd do w n. The unit runs down th rough th e m iddle o f th e swinga rm LO a ro cker arm th at pi vot s o n th e frame a nd is con nec ted to th e swin garm via (Con tin ued to page 26)

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