Cycle News - Archive Issues - 1970's

Frame your Yamaha By Tosh Konya We expect the best from motorcycle manufacturers and surprisingly several have co m e extremely clos e to filling our highest hopes. Last year the Hond a Elsinore was looked up on with awe and envy as th e light est, h est-handlin g ~IX m a chine. ava ilab le to the ge ne ral p ub lic. O th er m anufacturers were quick to pi c k up th e c ha llenge, whi ch re su lte d in suc h o ffejings as th e YZ Yam aha , Mag Hu sk y, an d Montesa YR . All o f these fantastic m ach ines perform o n a le vel far above the ave rage, • Underview shows how C-sect io n engine bracket, frame t u bes be gin to tie in. Object is to get neat boxsect ion ri gidi ty in swingarm ar ea. .. 36 "peasant model" produ cti on bike, but at a very dear price. Aft er laying out bigger bucks fo r purch ase, yo u ca n look forward to mu ch m a i n renan ce, replacement. and m or e maintenance. Works model production rockctships were d esigned for the pr o fessi on al rid er wh o d oe sn't mind putting m on e y in to h is b ike e ve ry week, as it is a so urce of income. We wh o on ly race for fun look upo n th es e e xoti c bikes w ith so me en vy. \\ 'e wo uld love to o w n a ro ck et b ik e bu t th e co sts o f runnin g suc h a m ach ine w ould quickly run us in to the poorho use . Besides the ligh t weight , all o f th ese bi kes hav e fiery powe rp lan ts th a t require cons ta nt carc . O ur 'e ng m es a re de pe ndah le , st ro ng enough, and th e p arts arc chea p , so we love the m for th o se reason s. U n fo r t u nately for t he wei ght-co n sci ous. the req uire m en ts of m a ss m arket ing d ict at e th at th e dependable fra me be m ade q uick ly an d o f a relatively in exp en sive stee l. Most riders accept th e fact th at th eir bike fram e is made o f " w a te r pipe" and ride h ap pi ly ever aft er . But a few o f yo u o u t here in moreland do care so we see k elsewhere for a frame t hat makes our "just average" hike closer to e xc el len t. One particul ar frame builder is Pro Pah . Like most a cces sory fr am es, t h e ir s is made of S ."E 41 30 c hro m e-m o ly st eel an d the welding quality and detailing m ake your stoc k frame look like th e firsl project o f a hig h school welding cl ass. The best part o f this frame . unlike most others, is that it will accept ali the stock Yamaha l\IXer parts excep t the shocks. Before going o n I'd lik e to clarify th at "all." Because this fram e was designed from scr at ch for seri ous racing a few th ings have been eliminated . Ther e is no ki ckstand or a u t o lub e tank br ackets, n or mo unting tabs for the st o ck skidp late . If y o u really think you ne ed a ny of these it ems, it will take a little time an d ingenuity to put them on. T he reason you need new shocks is t ha t the moun ts have been moved forward in th e cur ren t midshock fashion and are designed t o use 11.9·in ch , Husk y length dampeners. Slight trimming is required to fit the sid e number plates an d tw o new h ol es need to b e drill ed in th e stoc k air b ox. The vit al dimensi ons a re : 55,, " to 56 " wh eelhase, fork angl e 3 1 d egr ees . an d wei ght with a st o ck Y amah a 250MX ('73 o r '74 ) is ap proxi ma te ly 21 3 Ibs . dry. The e ng ine ap pears to b e far the r forward and slig h tly hi gh e r th an a stoc k Yamah a. Th e shoc ks have b een m ov ed forward four in ches and this res ults in 6" to 61'1" of rea r w h eel travel depe ndi ng o n t he shoc ks used. A n a lum in um b rake torque a rm with a n im proved locat io n helps 10 min imize th e hippe ty-h op w he n b rak in g d ow nhil l. Se vera l d e sign fe atures sa ve we ight and ad d stre ng th a nd lon gevi ty . The swi nga rrn p ivo t a nd a ll four fear engi ne mou n t ing tabs arc no w tied toget he r in a la rj1e c-c han ne l sect io n o f th e Pro Fab fra me. Thi s co ns truc t ion m ak es th e f rame, eng ine, an d swing-arm piVOI o ne rigid unit. A stoc ke r h as separ at e m oun t ing points for the en gin e and th e sw ingu rm , where so me fle xin g ma y occu r. The swingarrn rid es on a needl e-bearing setup co m pa red to the plast ic bushings on a stocker. T he lubi ng used is of several different diam eters an d wall thi ckn esses fo r o p t i m u m strength with minimum weight , A close lo o k at a stocker reveals a welder 's nightmare of large lubes slip pe d o ver sm aller o nes. The much -ne eded weight reduction does wonders for the on ce homely , yet fea r-inspiring Ya m ah a :'\IXer. Now that y o u have shocks that work, the lorks feel much be tte r, pl us ~emovinl( a ll that excess la rd doesn't hu rt! Wit h the engine moved forward the front wh eel washout of the past is gone. As you've read in many o ther p laces, the increased rear w heel trave l d oes wo nders for your co m fo rt and stability in r o u gh se ct ions, for example whoop-d e-do os. A t firs t it feels kind of mushy but you qui ckly acclimate yourself and gr ab for more th ro ttle an d a highe r gear with new co n fid en ce. The re a r w heel t ravel is on the co nser va tive side , com pa red t o others performing this mod ification , but I think for the time being this is an asset, for shock life (as fa r as I can tell) is still close to normal. Until a d rasti c improvement is made in -rear d ampers. it isn't wise to go for too mu ch travel, unless you ow n a shoc k abs o rber facto ry . With the weight reduc ti on, th e Yamaha 1\IXer is on p ar wi t h an Elsino re but will require very min or porting to ca tc h the swi ft and fragi le YZs. F o r th o se heavi ly in t o m o tocross bu t a l l e r g i c to a n ex pe n s i ve a n d parts-hungry m ount , th is m ay b e th e wav . T he Yamah a 1\IXer is o ne o f the c heapes t rac ing bi kes availab le , plus a ny o ne ca n swing a good d eal o n o ne by shop pi ng aro u nd. Th e ad di ti on al co st o f th e fra me an d shocks w ould put your sk o o t on p ar wi th a n ew Husky or CZ , fo r less tha n a Rad ial Mai co o r YZ. The price is relativel y inexpensive com pare d t o othe r fram es, plus y ou d on 't need to buy all th at extra st uff like a n ew l(as tank, sea t, still a ir box , side cove rs . e tc . These are the things th aI run the price of accessory frames sky high! The Pro Fab Yamaha kit (fits '73 & 'H 250 to 5 0 0 MXers) runs $42 5 . T his is fo r a frame, swi ngarm , brake to rque arm, a ll necessary n uts a nd bolts, pl u s some helpfu l in stru ctions for those of us wit h less than normal technical lQ. Add $50 to $75 for a se t of shock abso rbe rs, springs and you end up wi th a fair ly trick fram e /suspe nsion package, T he ProFab Yamaha kit is distributed by Bob May n ar d 's "Orange County Cycle " , 13666 Harbor Blvd ., Garden Grove, California 92640, phone (7 14) 530-7340. •

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