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/126501
I i'-'-'-'-'-'-'" II · NOTHING TOPS i !! i.\\AXIJ U! E i· ~ 00 ~ NOTHING!!! ! I . I . I • I i ~ · ~ I ~ ~ I i . = I.. I . I • I ~ ~ ~ I De-G....-ct Calor Fonlllecl A8cInt Cas1Dr PetroIeulII aI CJun BurnIng r--<:ycte 011 • · I I Fork OIl: 5, 10. 15 a 20 Wis. • I G_ 011: 1OW2O wt•• 1OW3llwl I • · · I I-MAXIMA OIL DISTRIBUTORS- • • I I IRON HORSE MIC SUPPLY • • ......,..T.... (713) 865-4321 I I • IkEL..URRY DIST. ·1 T8ft, c.Htomla I (lOS} 7IH7I8 • • MOTO-TAC DlST. I I ~Orwgon • • (S03)"~ I I PROGRE~VEPRODUCTS • • EJ ClJon, CIIIfomie (714) . . . . .12 I I • KE" PARK DIST. II Crucenta. CIllfom" I (213) 248-1. I • REED JOHNSON DIST. I I Whllll.r. Callfom" • • (213) 697·9444 I I "ALCOL" SMITH PROD. _ Rlwrslde. c.Htom.. • (714) 886-1006 I I REBEL SMITH DIST. • WhI11Ier. c.HtomII I I (213) 944 4453 • STEVE SCOTT'S MIC SUPPLY I I Woodland Park, CoIcndo • _ (303) 887·3378 I YOUNG CYCLE SUPPLY I • '""-'Ix, ArIzona • (602) 277-5401 I I PHOENIX PROD. • • Ceder Rapid•• low. I I (319) 382·3214 • • U.S. CYCLE PROD. I I Wabatar Grawe......~ • • (314) 988-3721. C.B.S. DIST. I I Spr:lIglOwn. PA • • . (215) 34&07304 I I WRITE OR CAll FOR FREE BROCHJRE· • "...,. . . . - . - I'lookICla I 11401 Plan..- WIly #1~ E1 CAjan. CA 92020. • (7141 442-9723 I DEALER INQUIRIES WELCOME __ ..-,. L I ._.~._._._._.~ RIDE AWARE Top competitors ~ insist on .,un alloy competition rims See your nearest dealer Sun Metal Pra ducts, Inc. P.O. _ 38 . . . . _ _. IN 48SlIO I ICloc:kwtu from top left) The key to Ya.hIrnura'. winning bike Is the 10Z3cc engine which puts out gobs of u~ IIbIe horsepower. Duel RGIiOO diaca end entkllve slow thInge quickly end...ely. Pet Eegen whips W.. CooleY. bike MMlnd RIveraIcIe Rec:ewey. HeevIIy guaeted awlngerm, KYB ahoc:ka end d1ffe1 .. tt .... fr8me geometry provide a188dy heI.ng lit ell speeds. drifting a bike. Instantaneous cross· ups at this speed are more scary than they are fun. But again, the main problem here was the coldness of the day greatly reducing traction. Another thing I became aware of: The faster you travel down a section of pavement, the more the bumps upset the bike. It might be that Riverside is becoming bumpier in its old age, but with the speed of this bike, I noticed bumps everywhere. The KYB suspension is super-adjustable and there is no doubt in my mind that with enough rime the crew and I could have had the rear end under better control. Back to the engine. The cases have had any excess material cut away and then they are Kal Garded. The crank· shaft is basically stock, but the bearing cages are specially manufactured of silver. To accommodate the Kokusan Dew COl, the left flywheel snout is shorter. After the crank is assembled, the crankpins are welded so that they can't move under the torque loadings. Yoshimura two· ring pressure cast . pisto.ns are used. P~~re _casting gives the highest strength-to-weight ratio. To get the maximum displacement allowed, special piston sizes are needed. 70.9mm bore with a stock stroke of 64.8mmgives 1,025cc. Fujio Yoshimura was reluctant to reveal what material the valves were manufactured from and would only say tbat it was special valve material. At 59mm, the intake valves are Imm oversize and the exhausts are 2mm larger than stock at 54mm. Like almost all ef the engine components, Yosh manufactures their own valve springs. Both inner and outer springs are progressive wound and use valve spring retainers made of aluminum. Valve adjustment is by a shim under bucket arrangement. Valve lift and timing specifications are: intake - 10.95mm maximum lift, openin~ at 50 0 before TDC and closing at 60 after BOC; exhaust - 10.4mm max lift, opening 56° BBDC and closing 26° ATDC. Cam chain is special Yoshimura "Gold," one link longer than stock. The extra length is needed because there is an added roller at the top of the head in between the cams. The automatic cam chain tensioner is modified to work as a manual tensioner. Porting is done by either Fujio or chief mechanic Suehiro Watanabe. The clutch hub and basket is basically the same as was specially manufac· tured by Suzuki in Japan for Yoshimura two years ago, but the clutch plates are different. Friction material is a paper base using 10 friction plates and nine Sleel driven plates. Clutch hub is sleel instead of the Slack aluminum. Transmission is Suzuki close-ratio as available through Yoshimura. . Yoshimura doesn't waste their time with anything which isn't aimed at getting the bike around the racetrack as quickly as possible. There are no frills on the bike. Getting everything to work in harmony is lheir main goal. They could probably sacrifice some mid-range in the powerband to gain some top end, but there's no reason to. The bike is the quickest and the fastest there is. And more top end at the expense of mid-range would only make the bike more difficult to ride.