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Yamaha XS 500
Road Test 1977
If you stay in one spot long enough, the sun will rise again and shine down on your head. Indeed the history of the 500cc Yamaha twin illustrates this proposition nicely. Introduced in 1973, the eight-valve Yamaha twin had the correct number of poppets, and an elaborate counter-rotating balancer to control vibration, but the bike was two short on cylinders. Or so it seemed at the time. Engine development was carrying Japanese manufacturers away from intermediate-displacement twins; multi-cylinder units had the momentum. Honda's investment in the future included the 500/550cc four-cylinder series, as well as the 350/400cc roadsters. Three-cylinder two-strokes, in 380cc and 550cc denominations, indicated Suzuki's direction, and Kawasaki ran the same course with its 350/400cc three-pot series and 500cc triple. Triumph's 500, Honda's 450 twin and Suzuki's venerable Titan sank back in a deepening shade. So despite its technical innovations, the Yamaha 500 seemed to be born with a five-o'clock shadow.
Still, Yamaha persevered with its 500 twin, changing its name (TX500 to XS500), reshaping its form (British curves to Italian blocks) and refining the bike's mechanical details. Meanwhile, Kawasaki pulled the curtain up the KZ650 four after bagging most of its triples. Suzuki celebrated the arrival of motorcycling's clean-air era by introducing, among other things, the GS550 and nudging the two-strokes toward a dark stage-right exit.
At stage left, however, a rising light illuminated Yamaha's spot once r The concept of the contra-rotating balancer, pioneered by Yamaha, spread to new Kawasaki twins (KZ400, KZ750) and then the Suzuki GS400. Then the new Honda 400s not only turned out to be twins but have contra-rotating balancers as well. Finally, a new crop of 500cc vertical twins popped up: Laverda has an eight-valve 500, Ducati offers the 500 GTL and 500 Desmo, and one Japanese manufacturer has a 500 vertical twin almost ready for production. Between dusk and dawn, Yamaha's competitors got twin cylinder religion.
Renewed interest by manufacturers in vertical twins of intermediate displacement can be explained in three ways. First, for all practical purposes, clean-air motorcycles will be four-strokes; as the most direct way to control emissions, all manufacturers must concentrate on four-stroke roadsters. Second, contra-rotating balancers can make vertical twins acceptably smooth, thus removing vibration as a major issue. The survival and success of the Yamaha 500 has probably done much to convince the motorcycling public (and other manufacturers) that a "balanced twin" is viable in the market. Had Yamaha botched the balanced twin concept, another manufacturer — even with a brilliant balancer — might have hesitated to try in a market where the idea had already failed. Third, in a period of considerable worldwide inflation, manufacturers — especially Japanese ones — have become cost-sensitive as the dollar continues to sink compared to the yen. The lower production costs of a twin-cylinder motorcycle look attractive when a maker must examine what customers can afford as well as what technology can build.
Alert consumers will spot the XS500D as a bargain. At $1550, the XS500D retails for far less than comparable motorcycles. The Yamaha is $150 cheaper than the Suzuki GT550, $180 under either the Honda 550K or 550F, a cool $200 less than Suzuki's new GS550, a whopping $350 under Ducati's GTL, and a gasping $750 beneath Benelli's ritzy 500 Quattro. The $1433 CB500T Honda undercuts the XS500D as does the Suzuki GT500B at $1295, but neither one of these dated twins (the Honda is really a 1976 model) could withstand a direct comparison with the Yamaha.
There's another way of looking at the XS500D's value. If you had $1300 in your pocket and were looking at 400cc four-stroke twins (Honda 400 Hawk, GS400B Suzuki, KZ400D Kawasaki and Yamaha XS400D), you would swoon at what another $250 stashed in your left shoe would buy. By any rational system of measurement, the Yamaha XS500D is a far larger, more detailed, more luxurious, more comfortable and better finished motorcycle than any of the 400 twins. On the other hand, once at the $1550 level, if you pulled another $250 out of your shoe, that second two-and-a-half simply wouldn't buy nearly as much as the first in the shoe $250. Beyond the price of the XS500D, dollars have a diminishing effectiveness: a lot more money buys little more machine.
At the center of the 500 Yamaha's value is its eight-valve, double-overhead-camshaft twin-cylinder engine with a counter-rotating balancer unit. The engine is a mixture of the simple and complex. It's almost as if there were two competing sub-committees that worked the engine, the Simple-is-Beautiful team and the Complexity-is-Progress group. At some point, in an effort to reconcile all factions, a Committee-of-the-Whole incorporated designs from both sides.
A double-row cam chain drives off the right end of the crankshaft and runs up a cavity outboard of the right cylinder. Simple. None of this cam-chain-up-between the-cylinders business for the sake of symmetry. Late C-models and all D-models have automatic cam-chain tensioners which supercede the old manual adjusters, so life is further simplified. By keeping the cam chain out of the center of the engine, the crankshaft could be kept relatively short and compact, and the center main in this plain-bearing engine could be wide and generous, extending from the left interior flywheel across to the right. Those who liked complexity got their way on the valve count: four-valves-per cylinder, eight in all. Since four small valves in this case have more area than two large valves in each cylinder, the XS500D can be a more effective air pump—which means more power. Furthermore, the four-valve system puts spark plugs directly in the center of the combustion chamber's roof, and this location gives better flame propagation and fuller combustion than spark plugs situated off to one side.
All this valve area and well-planned combustion-chamber design helped Yamaha engineers to build a 500 with a torque curve shaped like a high plateau and an engine with a good turn of power at peak revs. Not all secrets lie in the combustion chambers or even in the camshafts. Yamaha recontoured the inlet tracts on the XS500C models into order to get the twin to pull with more determination from 3000 rpm, and the 500 Yamaha has always had large capacity air boxes and mufflers which squelch noise without strangling the engine.
Yamaha used the XS500's design strengths in order to get a good horsepower without establishing a positively giddy redline and gathering a lot of horsepower immediately under it. Certainly the 500 does have poke—the engine develops about 1:3 horsepower per cubic inch; except for the GS550, the 550cc Yamaha twin produces as much or more horsepower than any of its competitors.
If the forces of complexity got eight valves, the advocates of simplicity must have designed the cam follower/rocker arms. Current practice, as seen on several Japanese double-knockers, has the cams pushing directly on bucket tappets on which or under which lie the adjusting shims. The tappets, of course, bear directly down on stems or caps. In all cases, to adjust valve lash is to change shims, and in some instances, to shim is to remove the camshafts. When time comes to adjust the valve lash, you have to find a service shop that has a complete set of shims, and service personnel willing to tackle the job properly.
The Yamaha system recognizes the human frailties; there are no bucket tappets and shims. Rather, the XS500D has cams that push down against follower-pads on fingers that pivot on spindles located beneath the cams. The fingers extend toward the center of the cylinder head, where the ends push the valves down. The fingers' ends have screw adjusters and lock-nuts, so the valve clearances can be set in a jiffy. Working room in the cam box is a little tight, but nothing beyond the Saturday-afternoon adjust-ityourselfer.
Weekend mechanics will be stopped dead under their shade trees by the Subcommittee-for-Complexity's most stunning achievement inside the 500's engine: chain-tension adjustment in the contra-rotating balancer system. You have to remove the left side cover, pull off the alternator rotor (special tool), remove the starter wheel and starter chain, and then take off the cover over the idler shaft in the balancer chain-drive system.
The balancer unit, which resides behind and below the cylinders, is driven by a sprocket on the left end of the crankshaft, via a long length of chain and two idler sprockets, one of which is set on an eccentric, thus providing a means for chain adjustment. The chain is disposed in such a way that it loops around the back of the balancer sprocket (between 12 and 6 o'clock) and then runs forward, engaging the crankshaft sprocket between 12 and 10 o'clock. In this way the balancer shaft turns in the opposite direction of the crankshaft. The two idler sprockets are located in front of the crankshaft sprocket, one below the crank sprocket and one above it.
The Yamaha owner's manual gives no indication at what intervals the 500's-balancer chain should be adjusted. Generally, however, this chain tension must be held within specified tolerances, and you'll probably know it when the fine adjustment is lost. A stretched chain may bang around and cause some noise—and balancer phasing can be upset enough to produce a new set of vibrations. Conversely should the chain be adjusted too tightly, the extra tension will bind the crankshaft slightly and make the engine idle roughly.
Since the Yamaha is a 180-degree twin (pistons alternately rise and fall) the balancer controls the rocking couple vibration in the crankshaft, that is, the forces which are trying to make the ends of the crankshaft churn around in circles. The balancer itself is simply two small half-barrels, phased 180 degrees apart, laid end-to-end on a single shaft. The unit looks somewhat similar to the one found in the GS400 Suzuki—another 180-degree balanced twin. The Suzuki balancer, however, is gear driven, a much more compact system than the Yamaha.
The Subcommittee-for-Complexity must have won the toss on the oil pumps. The XS500C is the only modern motorcycle that uses two oil pumps (both trochoidal type). The suction pump draws oil out of the oil pan, through a strainer, and then pushes the lubricant through an oil filter and thence to the crank and cambox. The scavenger pump pulls oil directly out of the lower crankshaft cavity, and then pushes the oil through the tachometer drive gear, from whence it bathes the transmission, eventually making its way back to the oil pan. By using two pumps the oil in the crank chamber can be kept at a low level where it cannot be stirred up by the crank, increasing the temperature of the oil and creating crankshaft drag. Furthermore, with two pumps and two oil routes the clutch chamber, transmission housing, oil pan and crankshaft cavity can all have individual oil levels set to their separate functions.
For as much engineering time and effort that went into the Yamaha 500 engine, the vertical twin remains unobtrusive: it's just there, working diligently away in the background. That's far different from the GS550 Suzuki or the Honda 550, the engines of which provides the rider with his strongest impressions of the motorcycles.
What isn't there is impressive. There isn't any significant engine vibration. You can lug the twin-cammer down around 3000 rpm where some juddering filters through to the pegs and saddle. In the real operating range of the motorcycle—and all the way to the 9000 rpm redline—the vibration-control system works. Indeed, in the "balanced twin" class, only the much smaller GS400 Suzuki is smoother, and not by much. The 500 Yamaha is easily smoother than any of Honda's new 400cc Hawks, not to mention the 400-series Kawasakis, or the KZ750.
The lack of jangling vibration makes the engine feel far more willing, and anxious to rev, than it otherwise might. That impression is strengthened by the soft, positive clutch and a gear-change lever that feels as if it's actually connected to a gearbox.
Probably the most disconcerting thing about the engine is its cold-blooded nature. Our test XS500D would not start, cold and sometimes hot, without flicking the cold-start circuit on. Even then, he who attempted to aid the start-up by opening the throttle was thwarted. The XS500D likes full choke and no throttle, or the whole starting business is just off. But know the drill, and you have no problem.
What everyone does notice about the X5500 is its beautifully supple suspension and luxurious comfort. Around town and down the freeway, the suspension—front and back—is incredibly active, snuffing out bumps and erasing ripples. Should you put a hand down at the fork leg wiper—even cruising down a road that appears glass smooth—you'll find the slider is very busy, removing the effects of tiny road irregularities. The blocky saddle, which at first appears too wide and too squared-off and much too over-padded, proves to be remarkably comfortable. Three-hundred-mile days will not punish your posterior.
Not everyone will find the XS500 suspension to their liking. Backroad racers will discover the front fork tops out easily, and the bike nose-dives into corners with hard braking making the rider think twice about the Ground Clearance (though it's good). Unless the rear shocks are notched up for greater spring preload, the XS500 will feel uncertain and indecisive over bumps in corners—a feeling that becomes far more pronounced in transient states from hard left-to-hard right. The Yamaha responds to steering inputs quicker than a GS550 or GT550 Suzuki, both of which feel more stable in fast corners, though that may be as much a result of their firmer suspensions as their slower steering geometries.
Until you're able to make the adjustment, there are a couple of peculiar things about the XS500. The footpegs are located farther forward than on most motorcycles, so your legs and feet seem unnaturally positioned. That results in more arm tension than normal as the rider tends to pull himself forward with his arms and put pressure on the small of his back. After a while (we had the XS500D for a couple of months) the rider's body adjusts to this position, and all seems well.
Whether you cruise the boulevards or stalk mountain roads, you will notice how the constant velocity Mikuni carburetors work the suspension. CV units (38mm at the throttle valve, 34mm at the venturi) provide a convenient way to use big carburetors to get maximum power at high engine speeds and still have a clean, immediate response off-idle and at low engine speeds. Alas, when constant-velocity carburetors are fitted to an eager engine with very little flywheel effect, rolling off the throttle drops the revs precipitously at which point the Yamaha lunges down on its suspension. Conversely, when power is applied sharply, the front fork can raise and top. So, if you want to imitate a frenzied rocking-horse, just flutter the XS500D's throttle open and closed. The driveline slop in the XS500D also aggravates this bucking effect. While Yamaha has steadily tried to minimize the driveline lash—by increasing the flywheel effect, changing to Mikuni CV carbs and tightening up the driveline components—the dial-a-lurch feature, though less pronounced than before, remains.
We suspect a good part of the suspension rocking can be traced right back to the soft, responsive supple suspension. And we doubt that many XS500D riders, once they learn to modulate the twistgrip carefully, would want to sacrifice the 500's primo ride in order to keep the suspension in a more even attitude.
Yamaha led the Japanese toward truly comfortable motorcycles with their stiction-free, teflon-sealed front suspensions. In addition, Yamaha was also the first Japanese manufacturer to mount quality OEM tires on their street motorcycles, a lead that Honda is only now beginning to follow. The Yokohama Speed Master tires fitted to the XS500D are soft and grippy enough, and put enough rubber on the road when cornering, to give the rider a real sense of security.
Yamaha still leads the industry in another area: brakes. The old Yamaha fixed-caliper disc brakes were always impressive, and though Yamaha switched to the less expensive floating-caliper design (front and back) on the XS500C, the braking performance was retained. Attention to detail in selection of disc materials, hydraulic ratios, lever positions, and basic quality control produces excellent braking: powerful, predictable retardation with a constantly solid and linear feel at the brake lever. The rear disc is just fine; we wish all rear discs, industry-wide, worked as well. The rear disc came as a natural consequence of the 500's cast alloy wheels—another feature which 550 Hondas and Suzukis have yet to match. A disc has far more swept braking area than any rear drum brake, and if the hydraulics or lever ratios produce an overly-sensitive caliper, the rear wheel can be locked up and skidded around unintentionally. In terms of weight to braking area, the XS500D is the class leader, thanks to discs fore and aft. With good tires and 3.52 pounds per square inch of swept braking area, the Yamaha XS500D can really stop.
The 500 does not go nearly as well as it stops. Running the quarter-mile in 14.9 seconds with a terminal speed of 88 mph is hardly dazzling performance from a full 500cc motorcycle, even if it does weigh 469 pounds. The D-times are much slower than the marks established by the XS500C in Cycle's Sporting Middleweight Comparison Test (August 1976 issue). The C-model cut a 14.6 second quarter and cleared the traps at nearly 90 mph. Yamaha service technocrats insist that there are no mechanical changes which would flatten the D-type's performance. In fact, there are very few changes at all between the C- and D-models, unless you consider a switch in the material of the head gaskets a change of earth-shaking import. Our impression is that the Comparison Test bike was probably a stronger runner, and the present D-type a weaker runner, thanks to production line variances in manufacturing. If someone were looking for a jet-fast bike in the 500/550 class, he wouldn't consider even the fastest Yamaha 500 he could find.
On the other hand, the XS500D is an excellent choice for a guy who wants a solid, non-threatening, intermediate-displacement motorcycle with real touring capabilities. Considering what the Yamaha XS500D features (cast wheels, supple suspension, disc brakes all round, vibration control, etc.) and what the bike can do (cruise in comfort and sport around on snaky roads), the motorcycle is a bargain at $1550, and well deserves its place in the sun.
Source Cycle 7977