Cycle News - Archive Issues - 1970's

1llll llll ll ltl tll llll ll ll ll ll Ull IUIll lll llll UIIlIII IIllUl Illl ll Ill lllll ll III Illl ll lll' IlUlll ll llt llll m 1IllUlll ll ll lllll lll llllll IIII1ll1l1l1I 11l1ll1llIIUllUll lll llt lJlIII IUlll l1ll1lUIIIIIIlIIIIl l11l l11t1l11ll11 lll llll llll l111 UlIl ll lll ll 1l1ll1II1II1II1l1II1llW1l1U1II1l1 l ' 1111ll1ll111ll1ll1l11l1ll1II1 11II1l1II1II1ll1llll lll lll llll ll ll ll lll lllll Factory works suspension for your bike Our Bell ows syringe, a Petrochern exclusive . injects FORK LIFE directly into the f orks. Pro v ides a ntt- f ce rn . -rust, -ox id at ion cha racteristics. H onda recommends ATF fluid. Av a il able in 10 t h ru 4 0 SAE . Cap grad u at ed i n CC's f o r ac c u r at e fil ls. Fill s pe cs on back of can . ~. . . . Ashland Chemk:al Company Ash/aDda Division of Ashland Oil, Inc. Santa Fe Springs, Ca 90670 Adolf Weil's 400 Maico exhibits the ult imate in handlino for a Grand Prix machine. By Jim Gianatsis With John Barclay and Bryan Kenny The 1973 World Championship Motocross Grand Prix series saw an exciting year. An American, Jim Pomeroy, won a Gr and Prix Petrochem CABLE LIFE MINUS 70 ' is formu lated s peoifically for snowmob il es a nd m otorcycles. Stays fluid to 70 degrees below zero . Aids in prevent in g throttle c a b le from freezing In the open position. Displaces moisture. lubric ates and rustproofs a ll moving parts. ......... Ashland Chemical Co. Ash/and. Div is ion of Ashland all, In c. ........i: Santa Fe Springs. Cal. 90670 SALES · PARTS·SERVICE Serving The Entire South Bay Area ~onttl)a DUCA" MOTO -GUZZ I M AleO M O NA RK D~ ~ -~-- 1244 NO. GAnn ST. SAN "010. CAU••90nl (ha rbor fwy at channel) 10 event for t he fir st t ime . T hree ti me World Ch ampion J o el Rob ert lost his 250 crown to Hakan Ande rsso n, a young Swede who everyone th ough t would ne ver ride aga in after al most losing his leg in a title race four years earlier . Roger DeCoster won h is thi rd World Ch am p ionship in th e 5 0 0 class after a y ear lo ng clash w ith Willi Bauer. It was also an inte resti ng year fro m a technical viewpoint be cause 19 73 saw rear suspension design adva nce m o re th an it had in th e pa st t en ye ars. Up until t his p ast year the trick t o b uildi ng a fast Grand Prix bik e was t o make it powerful and mak e it light. Th ose two prereq uisites no lo nge r ho ld true . By establishing minimum weight restrict io ns the F1M was ab le to make sure that everyo ne could have equal mach in ery o n that basis. Power wise , the mach ines ar e also very close because the ho rsep ow er race has given wa y to engine designs with broad , resp o nsive power th at the riders can con trol mo re easily . These changes left manufactu rers with only one alt ern at ive in t he design of building a faster mo t o cr oss machi n e, an d th at 's to make t he bi kes handle better. T he fir st pl ace to loo k was the r e ar s us pensio n where new design inovat io ns h adn' t occured since rigid rear ends wen t o ut, b ack in th e fifties. By im proving th e rear suspe nsio n two importan t factors are ga ine d . A bike tha t handles b et t er , especia lly over ro ugh ground wh ich is wh at motocro ss is mostl y abo ut , can go fas ter. Secondl y, a bike th at is easier to ride is less fatiguing for t he ride r, allowing him to ride closer to h is lim it fo r lo nger per iods a[ time , q uit e im po rta n t in 45 m inute motos. Yamaha and Mai co can be cred ited with bringing abou t the two m ost Bryan Kenny reworks a bare 250 Maico f rame at Pro Line Racing. Rear frame members must be cut. heated and bent, then rewelded with new upper shock brackeu. im portant innovations in rear suspension d esign during th e p ast year. The Yamaha monosh o ck design was b y far the most ra dical of t he two, and with it Hakan Andersso n w o n the 250 World C h a mp i on sh ip. Qu i te an accom plish ment for a design still in its pr o to t yp e s tages. The monoshock susp ens ion o f f e rs a numbe r of a d va n ta ges over co nven ti o nal shock abs orber rear susp ensi o n, among them incre a s e d r e ar whe el t ravel, less unsp run g w ei ght and proportional dampening. The monoshock sys t em also h as t he be s t potential for future development. Mai co has also b een doing testing with a monosho ck system similar to Yamaha's, but fo r the presen t they've chosen t o go with a design of th eir own, not quite as radical as th e monoshocker but similar in so me o f the benefits g~ned. They found that by lo cating convent ional-appearing rear shock abso rb ers up closer on th e swingarm to the pibot poin t th at rear wheel travel is inc reased . T he shocks tri ed have been shorter special de sign Bielsteins, that look very sq uat an d fat in an a ttem pt to m ain tain a larger reservoir with less vertical room in wh ich to design , and so me reworke d KONl's, agai n wi th th e o utsize flui d reservo ir nec essary t o effec t t he co m p r o mise between ade quate cooling an d shock travel. The advan tages are o bvio us . Increase d rear wh eel travel allows fo r a smoother ride over rough surfaces, allowing for easier control of the bike by th e ri de r . The advantages of Maico's id eas fo r reloca ti on of th e rear shocks were realized by most o f th e manufacturers on th e Grand Prix c irc ui t soon after the modified swingarms appeared. T heir performance on th e track backed up the id ea th at it w ould work and before long, Su zuki and Husqvarna GP bikes had the rear shocks relocated to in crease rear axle tr avel. Kawasaki has n ow fo llo wed the idea, firs t o n Torli ef Hansen's GP bike and then on th e T ran sAm b ikes, but wi th a little ingenuity of their own. The shocks are still mounted rela tively near the rear axl e, though moved up some. The mounts o n th e fr ame are relocated so th at t he shoc ks are o peratin g at a 45 de gree angle to the vertic al. Both ap proache s give more rear axle travel. Altering your bike The other tea ms o n th e G ra nd Prix circ uit co pied off o f Maico rather than Yam ah a for i mp roving thei r rear suspensions because Maico's idea co uld be p er form ed eas ily to the bi ke s th e tea ms already had in th eir possession without much trouble or ex pense. Th e mo noshock design required a co mp lete red esign of Yamaha's bikes from t he ground up . O nly two problems have co me up w i th Maico's design, b u t they ar e relat ively m ino r. The firs t is th at th e rea r shocks after bei ng relo cat ed w ill be subjected to m uch mo re worki ng st res s. This means heat and fatigue t hat not too many brands of shocks can stand up to, especial ly d uring the co urse o f a 45 minute mot o. KaNis ar e t he most read ily availab le sh oc ks th a t seem t o be able t o take th e punishment and both Mai co an d Su zuki are using re-worked versions on th eir wo rks machines. The thermal sh o cks that Yamaha and K awasaki a r e putting on their production motocrossers would also probably do th e job, if the fluid reservoirs will allow them to fit at the angle on your swingarm. Heavier weight spring s, up to 15 0 lbs, depending on rider weight, will be needed to go along with the in creased load on the shocks. between the pi vot o n th e frame and the axl e on the wheel may try to flex or be nd b ecause of th e stress po int being moved on th e swing arm to that area . Th is is eas ily. p reven ted with additional gusseting on the swi ng arm, bu t it doe s add a little to the unsprung weig h t. Th e m odifications shown in th is article are done b y Bryan Ken n y at his ' shop, .Pro Line Racing, in Tucker, Ge or g ia . Bryan w orks mainlv with Maicos, but he can perform the~e same

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