Suzuki RG50

GP replica

Old Bike Australasia - - CONTENTS - Story Jim Scaysbrook Photos Sue Scaysbrook

The orig­i­nal RG500 racer, which went into lim­ited pro­duc­tion in 1975 and was raced by Aus­tralian Jack Find­lay the year be­fore, is one of the most iconic and im­por­tant com­pe­ti­tion mo­tor­cy­cles of all time. Not so much for its string of world cham­pi­onships in the 500cc class, which were achieved by works or works-sup­ported ma­chines, but for the fact that the square four was pro­duced in suf­fi­cient num­bers to en­sure full grids in a class – de­spite be­ing the so called ‘pre­mier’ cat­e­gory – that was in dan­ger of ex­tinc­tion, hav­ing de­gen­er­ated into a re-run of the 350cc event. Now pri­va­teers could arm them­selves with a highly com­pet­i­tive and re­li­able ma­chine and go rac­ing with a rea­son­able chance of suc­cess, which went a long way to putting bread on the ta­ble for the im­pe­cu­nious jour­ney­men who roamed Europe.

But while the RG500, in its var­i­ous suc­ces­sive mod­els that cul­mi­nated in the Mark 12 of 1987 was God-sent for the race rid­ers, it didn’t do much for the road rider. That is, not un­til 1984, when Suzuki un­leashed the pro­duc­tion RG500 Gamma race replica on an unsuspecti­ng pub­lic. Well, maybe unsuspecti­ng might be stretch­ing the truth, be­cause Yamaha had stolen a march by re­leas­ing their own 500cc race replica, the RZ500, ear­lier in the same year, and spec­u­la­tion was rife that Suzuki would fol­low suit. No­tice of in­tent was served by Suzuki in March 1983, when the RG250 Gamma made its pub­lic bow – a 250 twin with plenty of race cred and said by Suzuki to be the first in a new ‘Gamma’ fam­ily. The ter­mi­nol­ogy, gamma be­ing the third let­ter of the Greek al­pha­bet, and pre­sum­ably in this case rep­re­sent­ing the third devel­op­ment in a se­ries, is a bit hard to un­der­stand, so maybe it just sounded right.

Then, late in 1984, at the IFMA Show in Cologne, there it was, perched high on the Suzuki stand – the road-go­ing RG500 Gamma. Just what was in­side the fair­ing at Cologne was not re­vealed, but clearly on dis­play was the alu­minium box-sec­tioned frame and Full-Floater rear sus­pen­sion, along with an anti-dive front end car­ry­ing the then-fash­ion­able 16 inch wheel. Nat­u­rally, the new RG500 was touted as be­ing a close replica of the ma­chines that had brought World ti­tles to Barry Sheene, Marco Lucchinell­i and Franco Uncini, but this was some­what re­moved from the truth. How­ever the ba­sic con­cept was true to the racer – a square-four wa­ter-cooled 500 with ro­tary disc-valve in­duc­tion, pok­ing out a very healthy 75kW at the crank­shaft and tip­ping the scales at just 154kg.

It was, as they are fond of say­ing in po­lit­i­cal cir­cles, “a coura­geous move”, given that two strokes were in­creas­ingly on the nose and im­pend­ing legislatio­n would re­morse­lessly drive fur­ther nails into the cof­fin of the ring-dings. The model, as both RG500 and the Japanese market RG400, lasted just three pro­duc­tion sea­sons, from 1985 to 1987. The RG400, cat­a­logued as the RG400EW, was iden­ti­cal save for the bore, giv­ing a ca­pac­ity of 397cc, with a 59hp out­put. To­tal pro­duc­tion of the 500 was around 9,200, with a fur­ther 6,200 400s built in the three years. Like the racer, the Gamma was ef­fec­tively two 250 twins dou­bled up (or more ac­cu­rately, four 125 sin­gles) with the crankshaft­s geared to­gether, with a cas­sette-style quick-change six speed gear­box. This com­po­nent was a boon to would-be rac­ers, with the gear­box in­ter­nals, in­clud­ing the shift­ing mech­a­nism and the kick­starter eas­ily re­moved by sim­ply tak­ing off the clutch and its back­ing cover. Con­nect­ing the cranks was a cen­tral shaft driv­ing the wa­ter pump, ig­ni­tion and al­ter­na­tor on the left side and the

wet clutch via a he­li­cal gear on the right. While the main frame was alu­minium box sec­tion, both the steer­ing head and the cen­tral swing­ing arm pivot sec­tions were in cast alu­minium, welded to the frame sec­tions. All of this was coated with a process called Du­ralite to pre­vent cor­ro­sion. The rec­tan­gu­lar sec­tion swing­ing arm it­self was also alu­minium, with a sin­gle cen­tral rear shock ab­sorber; the sys­tem, pi­o­neered on the suc­cess­ful mo­tocrossers, used the Suzuki name of Full Floater, with a ver­ti­cal shock ab­sorber be­hind the gear­box, and car­ried a 17-inch rear wheel. The car­rier for the caliper sat above the disc, while the torque arm was below, run­ning back to the frame. Up front were 38mm forks which car­ried one of the many forms of anti-dive that vir­tu­ally all man­u­fac­tur­ers were ex­per­i­ment­ing with at the time. Suzuki called theirs Posi Damp, and like its com­peti­tors, it was prob­a­bly more suc­cess­ful as a mar­ket­ing tool than in any prac­ti­cal sense. It was ac­tu­ally a means of pro­gres­sively in­creas­ing the com­pres­sion damp­ing, a sys­tem that had al­ready been tried on the heavy­weight GSX1100 EFE, with a choice of four set­tings. The idea of re­strict­ing the ten­dency of the front end to dive un­der brak­ing was laud­able, but it also had the ef­fect of cre­at­ing a hy­draulic lock in ex­treme con­di­tions, a sit­u­a­tion which pro­duced an al­most rigid front end just when you didn’t need it most. The fork legs them­selves car­ried air-ad­justable pre load­ing. Twin-pis­ton cal­lipers act­ing on a pair of drilled discs did the ac­tual stop­ping. Not sur­pris­ingly, Suzuki had its own acro­nym for the front brake sys­tem – DPBS – or Deca Pis­ton Brake Sys­tem (the com­pany seemed to have a se­ri­ous ad­dic­tion to Greek words at the time, Deca mean­ing ‘ten’). This sys­tem ac­tu­ally used ten small pis­tons, a to­tal of four in the two front calipers, and two in the rear unit – 4 + 2 = 10. Like Yamaha’s YPVS, (and later Honda’s ATAC – Auto Torque Am­pli­fi­ca­tion Cham­ber), the RG500 em­ployed what Suzuki called SAEC (Suzuki Au­to­matic Ex­haust Con­trol) – acronyms were the flavour of the month in Ja­pan at the time. Us­ing a ro­tat­ing bar­rel to raise or lower the ex­haust port height, this ef­fec­tively in­creased or low­ered the vol­ume of gas reach­ing the ex­haust pipe expansion cham­ber, and was con­trolled by the en­gine’s Ca­pac­i­tor Dis­charge Ig­ni­tion unit. All these sys­tems had the same in­tent and result – to broaden the power band by al­low­ing larger ex­haust port open­ings at high rpm, while re­duc­ing the ef­fec­tive size in the low and mid-range. In the RG’s case it meant a us­able power range from 5,000 to 10,000 rpm. The front pair of expansion cham­ber ex­haust pipes swept around the en­gine and un­der the crank­case in nor­mal fash­ion, while the rear pair came straight out the back of the re­versed cylin­ders and ex­ited on each side of the seat. The en­gine it­self mir­rored the later model race RG’s “stepped” lay­out with the front pair of cylin­ders lower than the rear. As well as ex­pos­ing the rear cylin­ders to the airstream, this al­lowed the gear­box to be brought for­ward, short­en­ing the en­gine’s front-to-rear di­men­sions. The road ma­chine used the bore and stroke from the orig­i­nal Mk1 RG500 – 56mm x 50.6mm – which wasn’t a stepped de­sign, but later came to be us­ing di­men­sions of 54mm x 54mm. The rec­tan­gu­lar slide-type car­bu­ret­tors sat on each side of the crank­case with air ducted from fil­ters mounted un­der the seat. Nice racer-style trim­mings like al­loy clip-on han­dle­bars, a re­cessed fuel filler in the 22 litre tank and an ex­cel­lent su­per slim fair­ing copied di­rectly from the track ma­chine added to the pack­age. There were of course prac­ti­cal dif­fer­ences be­tween road and racer, such as iron cylin­der sleeves in the seven-port bar­rels in­stead of Nikasil, but the pro­duc­tion road­ster when re­leased pro­duced only 4hp less than the orig­i­nal ‚

The RG400, cat­a­logued as the RG400EW, was iden­ti­cal save for the bore, giv­ing a ca­pac­ity of 397cc, with a 59hp out­put.

RG500 (XR-14) racer, de­spite the ad­di­tion of muf­flers and a com­pre­hen­sive air fil­ter sys­tem. Two stroke tech­nol­ogy, although un­der threat from the leg­is­la­tors, was now di­vided be­tween the schools of reed-valve con­trolled pis­ton port in­duc­tion, and the much rarer ro­tary disc valve crank­case in­duc­tion. In the case of the lat­ter, there were re­ally only two play­ers when it came to mass pro­duc­tion; Suzuki, and Kawasaki with their tan­dem-twin KR250. Ex­ces­sive crank­case width was one bug­bear, plus the ex­tra ex­pense of the pre­ci­sion ma­chin­ing re­quired. In the Gamma’s case, the front and rear cylin­ders fire 180 de­grees apart, so the pos­i­tive pres­sure in one crank­case helped to draw the mix­ture into the other as the pis­tons rose. Nat­u­rally, Suzuki’s tar­get was the Yamaha RZ500, and in many re­spects, the RG was su­pe­rior, at least in prin­ci­ple. It was lighter – by 26kg in dry form – more com­pact and slim­mer, but af­ter the clam­our cre­ated in Cologne in Novem­ber 1984, the Aus­tralian buy­ing pub­lic had to wait al­most one year for the ar­rival of the real thing. A ma­jor hur­dle of course, was mak­ing the new Suzuki com­ply with the Aus­tralian De­sign Rules and Euro­pean stan­dards, and this took time. And by the stage that the RG reached our shores in the sec­ond half of 1985, it was up against some se­ri­ous com­pe­ti­tion in the sporty road bike stakes, not just from the RZ500 but the stun­ning new FZ750, Yamaha’s five-valve rocket which would blow the wheels off bikes of far greater ca­pac­ity and horse­power.

Still, there were those who sim­ply han­kered for a real Grand Prix replica, and were pre­pared to stump up a fair wad of dosh – $5399 when re­leased in Aus­tralia – to own one.

Climb­ing aboard

Although I’ve rid­den a few rac­ing RG500s, which var­ied in spec­i­fi­ca­tion quite a bit from the Mk1 of 1975 to the fi­nal Mk12, I’d never had the op­por­tu­nity to try a road ver­sion un­til Dick Lip­scombe of­fered me a ride on his. It’s a re­mark­ably clean ma­chine that has had very lit­tle done to it since Dick pur­chased it a few years back from Old Gold Mo­tor­cy­cles at Lon­don­derry in Syd­ney’s north west. And while I have al­ways found the rac­ing RG500s cramped, with a high seat­ing po­si­tion and low-set han­dle­bars that ini­tially gives you the im­pres­sion that you’ll be launched over the front un­der se­vere brak­ing, the road bike, let’s just call it the Gamma, is en­tirely dif­fer­ent. The seat­ing po­si­tion is low and com­fort­able; quite an achieve­ment given that the fat ex­haust pipes are routed un­der the seat.

No elec­tric starter here, but the right-side kick­starter is a cinch to op­er­ate – just a steady prod is enough to bring the en­gine to life, but like the rac­ers, it needs a de­cent read­ing on the tem­per­a­ture gauge be­fore the bike will run cleanly or idle. While this was hap­pen­ing there’s a chance to take stock. The in­stru­ments con­sist of speedo, tacho and a com­bined fuel and tem­per­a­ture gauge – per­haps the most im­por­tant of the lot. The rest of the ac­cou­trements such as switches and levers are pretty much stan­dard Suzuki fare of the time. Now for some fun. De­spite the fairly lim­ited con­fines of the ‘test track’, the Suzuki is a de­light to ride. There’s plenty of flex­i­bil­ity in the en­gine and vir­tu­ally none of the old-world peak­i­ness as­so­ci­ated with two strokes. It feels like it would rev well past the 10,000 rpm red line, but there’s no point as power be­gins to drop off af­ter 9,500. It’s the beefy mid-range power that’s most im­pres­sive, no doubt a prod­uct of the Suzuki ‘power valve’ sys­tem. And there are more gears in the 6-speed box that I need on this oc­ca­sion in the in­ter­ests of li­cence preser­va­tion.

I re­ally wished this were a race track in­stead of a sub­ur­ban back street, be­cause the RG just wants to go, and tip­ping into cor­ners be­comes an en­joy­able ex­er­cise in weight shift­ing and throt­tle con­trol. The brakes are ad­e­quate with­out be­ing star­tling, but brakes like to be used reg­u­larly and this bike had not seen a lot of ac­tion for a while. I think the front stop­pers would have im­proved with a day’s rid­ing, but they were still per­fectly up to the task at hand. All too soon it was time to hand back the RG to its owner. Damn! This is the sort of mo­tor­cy­cle on which you could play all day. It’s easy to see why the RG500 Gamma has be­come such a cult ma­chine around the world, with nu­mer­ous own­ers’ groups and chat fo­rums. There are worth­while tips on tun­ing and main­te­nance, in­clud­ing how to push the stock 95 hp by around 40%. Now that would be worth try­ing.

ABOVE Launch ad for the new Gamma. LEFT Gamma. Third let­ter of the Greek al­pha­bet.

Rear set gear lever with its fancy link­age. Un­clothed. Big ra­di­a­tor and duct­ing lead­ing from carbs to the air box.

Float­ing rear brake with the torque arm run­ning di­rectly to the frame.

De­tail of the geared crank­shaft lay­out.

Pur­pose­ful rear end. The view from the cock­pit.

Se­ri­ous look­ing front end with Suzuki’s Posi Damp anti-dive sys­tem.

The RG500 Mk1 of 1976 rev­o­lu­tionised the 500cc class grid. This su­perb ex­am­ple is owned by Ray Moodie of Western Mo­tor­cy­cles, Pen­rith. The optional red colour for the RG500 Gamma.

Not Marco Lucchinell­i, just the ed­i­tor hav­ing fun.

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