1984 Yamaha RZ500

Yamaha has claimed for years that its two stroke twins are the next best thing to TZ racers with lights. Well, that may be open to discussion, but the RZ500 is an entirely different proposition. This is one model with a whole heap of racer in its makeup!

It has lurked at the edge of the motorcycling subconscious for the best past of a decade, the ghost-bike of countless idle hours, of innumerable doodle-pad sketches. It’s the “Wouldn’t it be great?” motorcycle, the universal dream of a GP racer with lights, its 300 km/h flash and stripped-down racetrack muscle softened (but only a little) in the interests of road legality.

Any firm brave enough could have produced it, but it’s pleasing to see that when the dream finally took shape, it had a Yamaha tank badge. No other company has held so steadfastly to the concept of fast road two-strokes, one or two steps removed from its racers.

The RZ500 is very close to our collective imaginings. It has a V-four cylinder layout similar to the OW71 factory racer (but a more street-orientated induction system); exposed rectangular-section frame rails and the two-up/two-down exhaust layout say this here’s a serious mutha. The solo seat, full fairing and tall, scalloped tank say it’s a good-looking mutha as well.

And the RZ’s dash matches its flash, as its debut win in the Hub 300 race at Lakeside in June proved. In a head-to-head racetrack contest it annihilates the 750 four-strokes, stomps on Honda’s VF1000, and is likely to be consistently bested only by Kawasaki’s GPz900.

It is slightly less amazing on the road, for where a conflict between the demands of the two activities has risen, the designers seemed to have plunked for the track.

This bike not only looks like a racer with lights!

It is also exclusive. The 1984 production run is tiny; the bikes involve a high proportion of hand assembly and worldwide demand has seen every one presold. If you’re in a frenzied state of sweaty palms and single-minded resolve, with the heater off and the grocery order cancelled in an effort to raise more cash, a path worn to the office of every finance company in town, the object of your passion may prove a little elusive.

The ’84 model RZ500 seems destined to be as rare and desirable as the green-framed Ducati 750SS of 1974 and is similarly likely to be the forerunner of a line of subsequent model updates.

Solidly mounted to the frame and all but hidden behind the fairing is the key to all the excitement, a V-four two-stroke motor loosely based on the OW71 GP racer. It’s an innovative design with definite racing heritage, a grand first for the road scene and obviously a source of no little pride to Yamaha.

In essence the powerplant is a pair of 250 cm3 parallel twins with their bores aligned at 50 degrees. The front two cylinders are laid nearly horizontal, while the rear two ride piggyback above and forward of the transmission. The two 180-degree crankshafts are geared to the clutch while a two-lobe balancer shaft set deep in the V is gear-driven from the front crank.

Yet the while the motor looks to be based on a pair of RZ250s, it’s closer in cylinder dimensions and porting to the TZ250, with bore and stroke of 56.4×50 mm to the RZ250s 54×54 mm. The TZ is slightly different again, at 56×50.7 mm.

A bit ‘o this and that

It’s also neither fish nor fowl in the intake area. Like the GP racer, it breathes through the middle of the Vee, but whereas the OW71 uses a pair of rotary discs the RZ500 makes do with reed valve induction, piston-controlled for the back cylinders, direct to the crankcase for the front. Two slide/needle carbs poke out each side, mounted on curved rubber inlet tracts. Air follows a quite tortuous path from the filter under the tank into plenum chambers inside each side of the fairing, and thence to the carbs. At the other end of the combustion process, both pairs of cylinders are fitted with electronically-controlled power valves, similar to those used on the RZ250s and RZ350s.

Exhaust gases from the front bank exit through the lower pair of chambers while the pipes from the rear cylinders follow the bulge under the seat to emerge from the tailpiece. None of the chambers are interlinked but the upper two cross below the rider’s posterior so that gases from the right side rear cylinder emerge from the left pipe and vice versa. The upper set are of all-alloy construction while the lower two are steel apart from the alloy mufflers.

At this point a burning question could arise. Is the rider totally protected from the heat buildup in the upper set of pipes? Not’ quite, as it turns out. Although there are copious quantities of a reflective material (which looks suspiciously like Alfoil) pasted on the inside of the fibreglass and a small heat shield under the seat the rider soon becomes aware of a source of warmth on the inside of the thighs and buttocks. The heat didn’t reach uncomfortable levels on test but after a good run the seat did become very warm to the touch.

This was handy since the weather was decidedly nippy during the test period but low speed riding on hot days could become a real pain in the butt for both rider and pillion.

Gadzooks! A kick start!

It was no surprise to discover that the RZ didn’t have a button labelled “start” on the right switchblock. One has to flip up the right-side rider’s peg, pull the kickstart lever back a little before folding out the sprung arm, activate the choke via a lever behind the left-side fairing panel, turn on the ignition, raise the right leg and kick once. The motor invariably fired up first time; after a few minutes the choke could be turned off (there’s no intermediate position between on and off) and the engine would settle into a smooth, even idle.

There was a need for quite a lengthy warmup before moving off, but since the cooling system has a thermostat, once underway operating temperature was reached very quickly. An electric fan helps keep affairs under control during hard riding.

Listening to the RZS00 at idle, it takes a few seconds for an unexpectant impression to sink in. It sounds for all the world like one of the RZ twins. The Two Wheels bunch are nothing if not sharp and it took us only a couple of hours of mental gymnastics to conclude that it should sound that way, since the diagonal pairs of cylinders fire at exactly the same time. On song, however, the effect is of two RZ250s jammed very close together, which is an amazing and beautiful sound quite unlike that of a lone twin, or even two in close proximity.

This magnificent wail certainly brings on images of performance on a grand scale. They’re images with a strong basis in fact. Maximum rear wheel power from the test bike was a superb 50.7 kW at 9000 rpm and specific power output a record-breaking 101.6 kW/litre.

The RZ puts out nearly as much as the most powerful 750 we’ve tested, Honda’s CBX750. Couple this feature with the low (180kg) dry weight and the result is inevitable: fiery top-end acceleration. The RZ500 becomes the proverbial rocketship once the tacho needle swings past 7500 rpm and stays that way to well past the 10,000 rpm redline. It’s a razor-edged sportster in the true spirit of the word.

And the not-so-good news

But being such a narrow-spectrum machine has disadvantages. The bike is far from good in some important areas. Power delivery is very peaky and gearing, though well matched to the top end, is too tall for the power on tap outside the 7500 to 10,500 rpm range. The six-speed close ratio box would be perfect on the racetrack where engine speed is kept high but in the real world all is not as rosy. Gear ratios are very similar to those used on the Kawasaki GPz900R but the RZ hasn’t anything like the low or midrange power of the Kawasaki four. Consequently, first gear is far too tall; a slipping clutch and 4000 to 5000 rpm are needed to avoid bogging down on take off, and if there’s a passenger aboard even more revs are necessary. Two-up, uphill starts are an interesting exercise, to say the least.

Even full-on acceleration runs are compromised by the combination of power and gearing. Compared with the likes of the four-stroke 750 sportsters, the Yamaha loses precious time and distance getting mobile. The gap might be narrowed with the outer-limits techniques of expert drag racers, but our less radical start procedures saw the 500 losing a good half second in the launch and the first 20 metres as it struggled to overcome the tall first cog.

In full flight, however, it is heaps faster than the 750s, and in fact will even peg back the likes of Honda’s VF1000 above 140 km/h. At that point of a standing-start contest, however, the VF has an advantage of over a dozen bike lengths, gained in those critical first few seconds. The RZ500 will run about the same speed at the end of the standing 400, but will lag by a good 0.6 seconds in elapsed time.

The combination of tall gearing and poor low rpm power dictates that a rider will rarely shift past third gear in the suburbs and on the highways will use fifth infrequently and sixth extremely rarely. Midrange power is better but good responsiveness even in lower gears cannot be obtained at engine speeds below 5000 rpm. For brisk acceleration in third a road speed of over 120km/h is a prerequisite, while fourth, fifth and sixth gear roll-ons need, respectively at least 140, 160 and 180 km/h on the clock for rapid get-up-and-go.

Bear in mind, though, that Yamaha makes no pretense that its latest drawcard is anything but a balls-out sportster. A buyer who expects to obtain scorching acceleration without a busy left foot will be disappointed. On the other hand, a rider who uses the RZ in the manner its makers intended will be in a permanent state of comatose delight.

Shakes and shimmies

Perhaps the most disappointing aspect of the motor is the rumble that emanates on trailing throttle between 4500 and 7500 rpm. Backing off at around 6500 rpm produces behaviour reminiscent of running over a pile of bricks. Even on a constant throttle between 5000 and 6500 rpm this unusual vibration is noticeable, while backing off increases the intensity. It’s a pity because under throttle the motor is quite smooth. There is a narrow band of high frequency vibration between 7000 and 9000 rpm but this buzzing is never bothersome.

It seems that the bitza induction system, high-speed-biased carburation and just-opening power valves get a little out of step with one another in the region of 6000 rpm.

Not as disappointing – mainly because it was expected – is the bike’s appetite for fuel. The RZ is considerably less economical than bikes of similar power such as the VF750F and GPz750 but is at least a little better than the hungry VF1000F. Speed-limit cruising will return around 16 km/l (not too bad) but turn up the wick and economy will quickly deterioriate to around 12 km/l or less. Still, constant flat-out riding won’t make matters too much worse ( 11.2 km/l) and around town the RZ will give you around 15 km/l. Performance comes at some cost, but it’s a small price for such scintillating zoom.

Stopping power is just as impressive as the go-power. The RZ wears twin 270 mm ventilated discs up front, a smaller 230 mm ventilated disc at the rear and twin piston fixed calipers all round. Performance under test was superb. The front brakes were fade-free, lock-resistant, and provided predictable, strong braking power with excellent feedback. Ditto for the rear stopper: only a small amount of sponginess in the front lever precluded a perfect score.

We found the transmission was not the most refined we’ve ever used, but it gave us no real cause for complaint. The shift action was a little vague and the clutch could do with a wider take-up zone, but overall it was capable, with little drive train freeplay.

Following the fashionable trend, Yamaha has designed a very flash frame for the 500. It’s a rectangular section steel double cradle unit with the lower pair of frame struts skirting the lower extremities of the motor and an upper set of two very wide tubes extending from the steering head to large steel plates incorporating pivot points for the swinging arm. Rear subframe rails run under the seat as far as the YPVS – emblazoned cowling, while the pillion section of the seat is supported by a separate bolt-on steel plate assembly.

Simple, effective suspension

Unlike Yamaha’s other supersportster, the FJ1100, the new two-stroke does not have a huge range of suspension settings. Adjustability in the front forks is limited to the hydraulic antidive while the underlying rear shock has five spring preload settings and seven-way rebound damping. Antidive force can be set by rotation of a small knob at the base of the unit and although the four positions are marked the absence of any positive stops means that any of an infinite number of intermediate settings can be used.

Adjustment of the rear shock is not so easy. The new linkage system has it located horizontally under the motor, a very sensible placement from a point of view of weight, but one that makes it necessary to crawl under the bike to set the preload (with a C-spanner) and the rebound damping. This is the only minor bugbear about the rear suspension. The RZ’s rising rate system is one of the best around. Even on the firmest setting the ride isn’t harsh, yet at the softest extreme bottoming out is rarely a problem. The suspension’s progressive action and quick compliance with small bumps is very impressive.

While the rear suspension performed faultlessly the front forks were not as well performed. The antidive does not appreciably reduce the rate of compression and the forks carry on a recent Yamaha tradition – they’re too soft. It’s quite easy to use all of the available travel during crash stops on smooth roads while any decent pothole will produce the same result. Heavier fork oil would help but stronger springs would probably be a more useful additional measure. On the bonus side, the bottoming out did not affect the bike’s stability to any appreciable extent. Generally, the handling was top notch.

With a wheelbase of 1375 mm, a dry weight of 180 kg and the sixteen-inch front wheel it would not be unreasonable to expect that agility is a very prominent feature of the RZ’s makeup – and it is! The bike is an absolute delight in tight terrain. Precise, neutral steering and the lack of flab keeps the rider always in touch with the machine and in total control. It is laughably easy to change line in mid-corner. High speed stability is top rate and steering doesn’t become overly sensitive at a breakneck pace. Both cornering clearance and the standard tyres proved excellent and the only impediment to superfast passage we uncovered by any stretch of tarmac was the tall first gear. On a few occasions it was difficult to stay in the powerband around very tight (15 km/h signposted) corners despite taking them at double the signposted speed plus a few km/h.

Perfection is elusive and the RZ does suffer from the odd sixteen-inch front wheel induced head shake, but the bike is better than the majority of current small-wheel models over rough roads and only a little worse than the best behaved of the bunch, the CBX750 and GPz900R. All in all the RZ is a brilliant handler, an extremely well-balanced and confidence-inspiring motorcycle.

Despite its single-minded nature, creature comforts have not been neglected. The riding position is biased towards the racer crouch but weight on the wrists is not excessive and although the footpegs are high they’re not set so far to the rear as to induce an uncomfortable bend at the knees. The seat is comfortable without being the plushest on the market; our pillion rider didn’t complain of any discomfort either, although less affectionate passengers might not appreciate the omission of a grab rail.

Instrumentation consists of a large tacho as centrepiece, a speedo on the left and smaller temperature gauge on the right. Warning lights for turn, low oil tank level, neutral and high beam are sited above the coolant temperature gauge. Switchgear is the usual excellent Yamaha fare. Headlight, tail light and horn all pass inspection and the mirrors were usable despite the rider’s shoulders blocking half the field of view. There’s no centrestand but the sidestand has a broad foot to compensate for the excessive lean.

Yamaha has done fairly well in the area of accessibility. The engine oil tank sits behind the fairing on the left side while the coolant reservoir is in a similar position on the right. The spark plugs for the front cylinders can be easily reached, while the rear set and the air filter are accessible by swinging back the tank on its rear hinge after removing a bolt at the front.

Quite a few people are going to be disappointed at the limited availability of the RZ500. It’s not going to be the sort of model that will be anything other than exclusive, although it seems certain that Yamaha is committed to continued production.

The exclusivity won’t be a bad thing, anyway. The V-four is not a particularly good motorcycle in the broad sense. It oils plugs and gets sulky in heavy traffic, drinks fuel at an alarming rate and has only adequate roll-on acceleration in the higher gears from sane speeds. That said, though, in the narrow range of riding activities which have production racing as their pinnacle, it offers performance on both a capacity and price basis the like of which we’ve not seen before.

By Dave Bourne. Two Wheels, August 1984

Guido from AllMoto has a look at an intriguing resto-mod RZ500 here.