Cycle News - Archive Issues - 1980's

~ ~ .--- - - - ------ - - - - --- - - ------ - - - - - - - - - - - --- - - ---- -,a: w ~ ...J 0: .... %~ ;< <'1M c z « Q c « a: « ~ « lr') 00 O"l w :; ...J ~ 00 .iU ... a:: w ~ 'm: 0: .0 E iU U iU 0 (A bove) The new CR might not look much d if f erent than la st year's. but performance is significantly better. (Below) Turning ab ilit ies and sus pens io n are the YZ's best qualities. Showdown: . . . . KXSOOBZ Kawasaki vs. CRSOOR Honda vs. TZ490S Yamaha The battle of the heavyweights By Kit Palmer H ere they are, th ree of J a p an 's finest and latest b ig-bore m otocrossers: the 198 6 KX500B2 Kawasaki, the 1986 CR5 00R H onda and the 1986 YZ490S Yamaha. T he big q uestion is. which one is the finest? Is it the reigning champ, the slightly refined CR500 Honda? Or is it the KX500 Kawasaki with its front and rear disc brakes and a new power valve? Or is it the mostcha nged , but still air-cooled, YZ490 Yamaha? There ca n be no easy winner in this heavyweight bout, that's for sure, but th ere is a winner, nonetheless. 10 Techni cal H onda : The 1985 C R H onda wa s th e kin g o f th e class with its p ow erful .m o to r and decent sus pen sio n , so it 's not su rprisin g th at th e H onda is th e least cha n ged of th e three. Mu ch em p has is went to make th e I 6 CR Y ,,"_ .U •• J. \ •• .;.~,.. 1 even easier to ride than the '85 Honda . because many Honda owners felt the throttle response was a little too explosive. To alleviate that problem , th e ignition co il, timing and cylinde r head were a lte red . The ignition now provides a stronge r and a longer duration spark, while th e new cyli nder h ead 's larger co m bustio n cha m ber low er s the co m p ress io n, cha n ge which also makes th e bike eas ier to sta rt . Th e piston h as a new profil e.to red uce excess ive roc king aga inst th e cylinde r wall s for added dura bilit y. An d to red uce weight. th e twin ra dia to rs have two wat er cores instead of three. ., T he ex ha us t pipe has the sa me d im en sions as befor e but th e rebuild - a a b le al u m i n u m si len cer is n o w mo un ted to the fra me in two p laces - in stead o f o ne. Ca r buretio n is handled - by a 38m m fla t-sli de Keihin th a t feed s in to a reed- va lve ind ucti o n cha m ber. a nd breat h es through a la rger a ir bo x a nd foam filt er. T he five-speed internal transm issio n ra tios are unchan ged but th e co un tershah sp rocket has o ne m ore . tooth. T he shi fting fo rk a nd dogs are redesigned for added stre ngth , while th e m a in sh aft, clu tch co llars, shift spi ndle a n d kickstarter idler gea r are made lighter. T he wet, multi -plat e cl u tch is basica lly th e sa me except fo r th e li fter arm being sha ped differen tly to ac h ieve a ligh ter feel o n th e cl u tch lever. Th e 1986 fra me has th e sa me d imensions as th e '85 CR, but some of th e stress points are beefed up. Front and rea r sus pe ns io n is revamped with mos t of th e a tte ntio n going to th e forks. Th e Sh owa-made, a ir-adjustable, 43mm forks are a lm ost exac t replicas of th e ones used on the works bikes, which have th e new car tridgetype damper assem bly. The wh ol e damper assembl y works inside a cartridge, out of reach from air bubbles that form outside the cartridge when the fork is hard at work. The primary advantage of this system is to maintain constant damping action. Front wheel travel is 12.0 inches. Blue fork boots protect the stanchion tubes. The Pro-Link, single-Showa-shock rear suspension is refined for more progressive action by shortening the length of the bottom link and modifying internal dampingva lving. The shock is still fully adjustable with 18 external compression damping and 2 1externa l rebound damping adjustm ents. The box-aluminum swingarm now pivots on needle bearings instead of bushings. R ea r wheel travel is 13.0 in ches. A common problem that plagued many '85 C R500 owners was exploding rea r wheel bearings on th e drive side. To cu re this problem, Honda added two bearings to this side as well as h aving one on th e oth er. The new hub also a llo ws th e use of 3mm wider brake shoes for stronge r braking power. Other . cha nges include different drill pa tterns in th e front disc brak e to red uce we ig h t, gold-a nodized rims, ru bber-mou nted handlebars, Bridgesto ne M-26 and M-24 tires, a nd a slim mer gas tank a nd seat. The whole p a ckage weighs a n a ctu a l 248 .5 p ounds wet. Yamaha : Of th e three bikes, th e lllJ~ 1..LLIloU o&.LILI ~ •• .ac ...... YZ490S is th e m ost ch a nged , internall y a nd cos me tica ll y. The biggest cha nge to th e '86 YZ is th e swi tch fro m a four-speed to a five-speed transm ission with fifth gear having th e sam e gear ra tio as last year's fo urt h gea r. T he pull lever o n th e cl u tch rod is ex ten ded to mak e cl u tch lever pull lighter. The air-cooled, 487cc eng ine received a few ch a nges. The left-side sca vengin g port was reshaped for two reasons: to give th e Yamaha better pun ch at midrange, a nd to im p ro ve relia bility. The way th e left -sid e sca venging port was sha ped in th e 1985 m od el. there wa s a weak point at the bottom of th e cyli nde r wh ere it mat ed with th e engi ne ca ses. The cylinder wall wa s too thin a nd would crack; th e reshaped scave nging port allows th e use of thi cker walls (5m m from 3m m ), eli m in a ting cracking problems. Bore and stroke remains unch an ged a t 87x82m m; th e 6.9:1 compression rat io and 40mm round -slide Mi ku ni ca r bu reto r are also h eld o ver unch a n g ed, a lt ho ug h j ett in g wa s chan ged slig h tly. T he carburetorfeeds into a fu lly-reeded induction cham ber, but the materi a l o f the reeds have been changed to improve th rottle resp onse. The reeds a re no w made o u t of resin in ea d.-Q[ steel. ~~t T he a irbo x is reshaped to improve a ir flow an d has been redesigned for easier mainten ance. Sus pe ns io n o n th e Yam aha went th rough m aj or cha nges, mainly in th e rear. An Ohlins shoc k with th e Brak e Actua ted Suspension System (B.A.S.S.) is used, bu t in stead of working o n linkages above the swingarm , th e shock no w ru ns through th e swi ngarm and co n nects to the lin kages undernea th . To accom moda te th is new sus pe ns io n system , the frame is co m p lete ly red esig ne d; changes incl ude the hea d pi pe bei ng len gth en ed I Omm and the area around th e swingarm pivot mad e stronger. T he a ir -adj us ta ble, 43mm Kayab a fork offers 11.6 in ch es of wh eel travel. as well as ex tern a l co m p res sio n damping adju stments. A supe r-hard coa ti ng o f Alurnite is used in th e fork slide rs to keep th e oil from ge ttin g co nt a m inated by m etal particles that usually wear off th e sliders under use. Alumite's o ther advantage is that it also reduces st iction. The new Yamaha also features a sma ller front disc brake with improved pads, a smaller hub, gold-anodized aluminum rims, M-22 and M-23 Bridgestone tires, Z-spokes, a muchnarrower fuel tank with 2.6-gallon capacity and a lower center of gravity, new waffle-pattern grips, and new side panels and graphics. Kawasaki: The new KX500 Kawasaki features two major additions. the Kawasaki Integraded Powervalve System (K.I.P.S.). and a rear disc brake. which replaces the stan da rd drum/ shoe set up. The K.I.P.S. is the first (and only) power-valve system offered on a production big-bore motocrosser, and is designed to give the KX strong low end without sacrificing power at high rpm . Since the KX now has KJ.P .S.• the boost bottle used last year is now his tory, leaving only the Yamaha with a boost bottle. Like the Honda, the Kawasaki is water-cooled, with two separate radiators mounted in front o f th e gas tank. The twostroke motor ma intains its sq uare bore and stroke con figuration at 86x86mm, 499cc actual displacement and 40mm round-slide Mikuni carburetor, bu t th e co m p ressio n ratio was bumped up to 8.0:1 from 7.9:1. T he o n ly o the r cha nge inside th e motor is th e eig h t-peta l (fo rmerl y six) reed valve. wh ich now has ca rbon fi ber petal s. . The KX has ca rr ied over (fo r the

• Cover