Cycle News - Archive Issues - 1980's

-·, ' · '/ r ~(J500 /~ ;f.~ ~I~~, ........ - :;:~ ' 4.; ". By Chris Knowles /Cycle Canada . Take a Suzuki 'R G 500 G a m m a racer sti ll h ot from g rand p rix competition, add lights, license, kick it ov er a n d take the rest of the day off. Every rider's fantas y? Sport for the weal th y? Nei ther. T he 1985 Suzu ki R G SO is rea l, a nd it' s O as close to a n actua l rac er as th e law w ill a llow. Come, ta ke a look . Racing purist s oft en snee r when a producti on vers io n o f a co m petitio n machine is rewarded with th e h al low ed name a nd co lo rs o f th e racer. Often the pse udo-racer mass-p roduced by th e facto ry bears o n ly pass ing resem blan ce to th e machine pa in staking ly hand -wrough t i n th e R &D dep artme n t. Not a bl e exc ep tio ns ha ve been p o p ping up wit h so me frequen cy in th e last lilli e whil e. Yamaha 's 500cc twostro ke wa s given the RZ p refix rather than th e o wne r's OW. alt ho ugh i n some respects it was a dead-ringer. But n o street-go ing m o torcycl e mor e deserv es to in heri t a fa mous racing designation th an Suzu ki 's n ew RG500 Ga m ma , We too k ou r wre nc hes to a n RG 500 to fin d out JUSt ho w clo sel y it m im ics race des ig n. a nd h o w it compares wi th its na tu ral riva l. the Yamaha RZ500. H andl ing th e spa n ners was Wes P rall . mechanic to Tom H er ron whe n he wo n th e Isle of Man 'TT a nd Barrv Shee ne wh en h e wo n h is two 500c~ Wo rld C ha mpio ns hips. Wes is now techn ical tra ini ng co-ordi nator a t Suzuki Ca nada in Toronto. The G amma pro to type we di sassem bled in fact had a 400cc en gi ne, which will be bored to 492cc for Ca nada and o the r market s. T he prototype was ro ugh in spo t. T he Gamm a us es a sq ua re-fo ur. two -stro ke, liq u id -coo led engine wi th rota ry-val ve induct ion a nd Suzuki 's own version o f a variable-size exha ust cha mber. ca ll ed Aut omat ic Exhaust Control. T he cylin ders a re stepped - the rea r two sitti ng hi gh er th an the front two - to a llow th e gea r cl uster to be mo ved forward fo r a mor e co mpact en gi ne, a nd to ex pose th e rea r cylinder head s to some cooli ng a ir flow . Alt ho ugh the mo tor is liqu idcoo led . th e rea r cylinde rs o n th e rac e bike wer e pron e to deto na tio n un til the step ped co nfig uratio n was adopted in 1978. T he Suzu ki sq ua re -fo ur design a pp eared in 1974 as th e RG 500 (facto ry de signation XR 14) to rep lace th e T R5 00 p a ra ll e l twill. ' Maximum hors epow er wa s 100 a t 11,200 rp m. The RGA500 with its stepped cylin ders a nd sq ua re bore a nd stro ke was un vei led in 1978. p roducin g 122 h p a t 11 ,000 rpm . T h is stepped- four co n fig uration ca n actua ll y trace i ts roots back to th e Czechoslova kia n j a wa racer of th e late I950s . T he lat est Suzuki racers sti ll usea simi la r desig n , but now hav e AE C cha mbers and p rod uce more th an 140 h p. Thi s seven-year-o ld eng ine design is o n ly now falli ng behi nd th e H onda and Yama ha leaders on th e G P circ u it. As a de-t u ned en gi ne for a stree t bik e it sho u ld be relia ble, strong a nd eas ily coa xed to produce mo re power. T he ho rsepo wer fig ure being m enti o ne d is 96, co mpared wi th a n a lleged 8.5 fo r th e RZ. ., T h e Ga m ma engi ne is a lmos t " ide ntica l to th e race engi ne in so ma n y ways th at it 's possi ble so me parts co u ld be int er ch an geable. T he cra n kcas es o n both mo tors sp lit horizonr alt y to ex pose th e cran ksha fts, wh ile th e tra ns m ission a n d sta rter sha ft det ach in a cl us ter from th e ri g h t side af ter remov ing th e clu tch co ver a nd wet cl u tch . G ell ing a t th e tran sm issi on , th en , i nvo lves o n ly rem o vin g 10 bolts in th e cl utch co ver , four bo lts holdin g th e.clut ch springs, th e cl ut ch nul a n d t h en seven screws hol ding th e case pl at e th at secures th e co u ruersha ft, sta rt er a nd ma in shafts. Th e pr im ary sha ft, locat ed on th e sa me p la ne a s the co u n tersha ft a nd main sha ft, is removed sepa ra tely. All this ca n be done w it h ou t rem o vin g the engine from th e frame. H an d y. W ith the ra cer 's d ry cl utch m ak in g d isa ssem blv even easier, G P me cha nics ca n dr~in th e oil. remo ve the transmiss io n , ch an ge a gea r in orde r to get th e p roper rati o for a part icul ar track o r j ust a part icul ar rorner: a nd be back o n th e grid in 20 minutes. It appears that fillin g a race-spec d ry clut ch to the prod uc tio n RG will not be poss ible. T he cl u tch, w ith eig h t fiber a n d eig h t metal pl ates, is sma ll for a n en gine of this h o rsepo wer (a ga in, thi s is a p ro tot yp e 400, a nd spe cs co u ld cha nge prior to producti on ). Th e p ri m ary p in ion an d th e cl u tch gear i t m at es to are heli cal. un lik e th e racer wh ich uses strai ght-cut gears throughout. Helical gea rs lose a bit o f power to frict ion , but run qui eter. T he clutch ge ar an d t he p inion o n th e prim a ry sha ft a re both cush io ned wi th in tegr al spr ings. T he race bike's transmission sha fts are slig h tly la rger than th e production bike's, but th e gea rs a re a bo ut th e sa me size. Each bank o f cyli nde rs ha s its own cra n ksha ft. T he two cra n ks a re gea red to th e main sha ft an d rot ate clockwise, aga in like th e works bike, with di a go na lly-op posed cylin de rs firing togeth er. T he main sha ft also drives th e water p u m p , located a t the bottom of theengi ne, a nd the cl u tch gear o n th e righ t a nd the ignition o n th e left. T he original Suzuki squa re-fo ur ' had a tran sm issio n o il pump, bu t it was deem ed u n nec essary a nd elim inated. T her e isn 't o ne o n th e street RG either. Also not necessa ry because of th e square co n fig u ra tio n is a bal an cer sha ft , as used o n th e RZ. Vibrati on is damped by rubber en gi ne mou n ts. T he RG 's co n ncct ing ro ds arc thin ncr than the wo rks units. Both en gines usc rol ler bearings. with th e rod big end flo atin g a nd th e sm all en d center ed bv sh ims. Thi s a ll o ws t he rod to cen ter ' itself in th e cvlinde r ra ther than i ts p osition being di ctated by big-en d location a fter the cra n k is p ressed togeth er. T he re 's a lso less ro lling resis ta n ce becau se th e big en d isn ' t pressing aga ins t thrust was hers, a nd the re 's more roo m bet ween th e rod a n d th e cra nk we bs for lubricant to reach th e bearin g. At both en ds of ea ch cra n ks ha ft are rotary va lves to co nt ro l mixture intak e. Eac h valve ex poses th e intake port when th e p iston is o n its co m - pressio n stro ke a nd th en rot at es to cover the port o n I he power stro ke . T h e rotary-val ve system is us ed o n the S uzu ki , Yama ha and Cagiva 500 G P racers as well as o n the succ essfu l Rot a x 250cc GP bike. Rot ary valves a llow more vari ed a nd precise in ta ke tim ing than ,w i th o th er designs. Flat-s lide Mik uni ca r bs (29m m o n th e 400 prototyp e) mount o n eit he r side o f th e en gi ne and a llow for a short in ta ke tr act. Th e car bs ar e so co m pact a nd so close to th e engi ne tha t they don 't protru de far p ast th e protecti on o f the alumin um fra me members; th e bik e, li ke its ra ci ng co us in , sho u ld surv ive m ost slides o n its side without maj or car b damage. T he 'p ro d uctio n R G in 400cc form has six ports per cyli nder, compared z ~ w 5 u rJl >- '" rJl o b :r 0. Assembled RG500 street engine is compact. (Be low) The transmission pulls ou t as a u nit from the right side after the clutch is pulled. 17

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