Cycle News is a weekly magazine that covers all aspects of motorcycling including Supercross, Motocross and MotoGP as well as new motorcycles
Issue link: https://magazine.cyclenews.com/i/127291
riva l Suzu ki which sported similar hardwa re, these were not of the pow erjet variety which beefs up the midrange - the Yamaha already had a good spread of power without resorting to th is. The eight-port cylinders (four tra nsfers plus one boo st port, matched to a single large exhaust port with twin supplementary ports) were revised , with round external castings and heads that trimmed a litt le weight, bot rumors of carbon-coated pistons and! or cera mic head inserts enabling the team to run sky-high compression ratios were j ust tha t, according to R a in ey's ch ief m ech ani c H ow a rd Gregory, who ' toge the r wi th race engineer Mike Sinclair and back-up wren ch Bernard Ansiau were responsib le for looking after th e title-winning machine, whi ch remark ably enough didn 't suffer a si ng le m ech anical breakdown in a race all season - no wonder the YZR500 has earned such a legendary reputati on for reliability. " It's certa in ly tru e that o ur bikes had a different exha ust note than th e other Yarn ah as,' admits Gregory , " more of a shriek at high revs which some people thou ght mean t we had special engine internals compared to Garri ga and So nau to. Bu t apart Irom th e power-up kirwe go t a t Lagu na Seca (new pipes and cyli nders with revised porting) which they had to wait till Assen to have, the bikes were the same specification, on ly we had our carburation set up ideall y every time, and the engi ne as close to perfect as it was possible to get , thanks to the feedback fro m the on-board comp u ter system we used to set the bike up in practice. T hat mad e a big difference." Team Roberts was the first 500cc team to emp loy telem etry a t race meetings, starting last season, an d ' under compu ter wizards Tom O 'Kane and Paul T reacy the facility reall y came into its own in 1990. Thanks to. the on-boa rd record er, the team was able to reap full advantage fro m testing and qualifyin g sessio ns, removing the ra mcard computer from the b ike for th e race to save weigh t. By th is tim e, the data collected would have.ena bled th em to mak e dozens of cha nges in quali fyin g to both engi ne and especially chassis specifica tion in a self- developed back in Japan with Taira. - that appeared from time to tim e. " Apart from some titanium exhausts that cam e through for Czecho to try to save a bit of weight but were the same design as the ones we'd been . using up till then , we ran the motor in Lag u na Seca spec all season ," says Howard Gr egory . " It hurt us giving horsepower awa y to th e others, but at least it meant the bik e was reliable that's always 'been Yamaha 's policy, and it paid off." That meant the carbon clutch developed by th e Roberts Team in conjunctio n wi th brake supp lier AP-Lockheed never progressed beyon d the pro totype evident ly largely successful search for the op timum setup. Considerin g that the Ohlins inverted fork (wi th goldcoated sliders to resis t carbo n buildup from th e front brakes) has no less than 20 rebound and 18 comp ression settings, while the rear Ohlins shoc k ha s 18 reb ound a n d n o less th an 26 compression positions, coup led with a range of offsets varyin g the trail from 97 to 106mm and a cho ice of hea d inserts ena bling the fork angle to be varied between 24.5 and 26 deg rees, q uite apart from the abi lity to alter the wheel base or ride heigh t at the rear, the need for telemetry to cope with the multi-adjustabili ty of the modern facto ry GP racer could hardly be understated. T hrow in anything up to a dozen development tires to be tested at each race as part of Miche lin 's ongoing test program, and the desir e for more track time a t each race becomes understandabl e - eit her tha t, or less so they can go private testing in bet ween G P racesl Rainey star ted th e seaso n in Japan with an updated version of the 1989 Yamaha chas sis, already debu ted by factory tester T adahiko Taira in the en d-of-seaso n Sugo intern at ional. boasting a shorter swingarm to move weig ht rea rwards in search of improved tract io n an d reduced weight tra nsfer under braking, and a steeper front end geo metry to improve the Ya maha 's steer ing in turn s. Bu t thou gh Rainey won that first race, he was n ' t happy wi th the Yama h a 's cha ssis beh avio r, especially compared to the more nim ble Suzuki wh ich emerged as his mai n riva l for the title with Kevin Schwan tz aboard, which also appeared to· have th e edge on top speed. How ever, it wasn' t until th e British G P a t Don in gton , two-th irds of the way through th e season, tha t Yama ha prod uced a revised chass is for the YZR500, with the engi ne locat ed lower in the 'frame and moved backwards 15mm relative to the ax les, an d an adjustable swingarrn p ivot givi ng 4mm variat ion up or down: after some experimentation, Rain ey sett led on the origi na l setti ng, and likewise discarded the various power-up parts - of ten stage, thou gh it 's still being worked on : Apparen tly one problem to be overcom e is keeping the plates warm , because when the y're cold, there's no drive , till they suddenly grip, with imaginable results! The problem of dust has to be addressed, too, though wear is very sligh t and this is no t a .serious factor. A damp but sun ny autumn day at Sne uerton provided less than idea l 'co nditions to come to terms with Wayne's 160 bhp-p1us weapon , but in a way it exposed th e Yamaha 's strongest su it - its now famou s usab ility. Having been honed and refined over the best pan of a decade - during which it 's ga in ed four Wor ld Ch ampionship titl es in tota l - the YZR500 may not be the fastest or the mos t nimble bik e in the GP pack , bUI it is the best a ll-ro under . The Yamah a 's impression of usability becomes imm edi ately ap pa rent as you trickle out of th e pits onto a dr ying track, with enoug h wet patch es still around to mak e inte rmedia te tires th e hot tip on a coo l day. T he Yamah a will drive from practica lly zero revs withou t slip p ing the clu tch , yet when it comes into the po werba nd from as low as 6000 rp m upwards , the eng ine doesn 't explode into life - things just suddenly sta rt happening a lot faster! Though Yamaha doesn 't yet have Honda 's three-way comp uterized link between throttle positions, revcou nte r and ignition to contro l the operation of their dru m-ty pe powe r-valve, the simpler Yama ha system is extrem ely effec tive in co mbination wi th th e po rti ng of the new cylin ders, which for 1990 had revised mounting points to stop th e boss cracki ng at the base of the casting , as well as a .new water system feeding co ld water to th e ex ha ust p ort from th e tw in-s tac k radia tor: this reduced run ning temperature to a hyper-efficient 55 degrees, rising only to 65 degrees in the Le Mans or Donington cau ldrons. A side choice of altern ative opening curves for the power-valve is obta ina ble depending on what chip vou fit to the Nippo n-