The Motorbike Archives

Well, sorry. You square-jawed heroes who think Seventies-style motorcycling has gotten soft without sprained ankles and brightly colored hematomas will find little of the 1950s in Yamaha's SR500E. It's not a revival machine that transports the aches and pains and oil leaks of 1952 forward to the threshold of 1980. On the contrary, this 500 single is a thoroughly modern motorcycle.

To say that the concept—an agile 500cc four-stroke single—is "old" misses the point. Sometimes a good idea seems to be frozen in metal, inextricably tied to a particular set of machines in a given time-frame. But a good idea is a really timeless thing. And so the big-bore single-cylinder roadster has come back; rethought, re-engineered and reconstituted in all its mechanical specifics.

Yamaha's new street bike has been developed out of the XT500 and TT500 dirt bikes, but even here the lineage tends to be more apparent than real. The SR500E is not a street-bike adaptation of the XT500. To be sure, TT, XT and SR all have 87 x 84mm engines, and the XT and SR units both have 9.0 to 1 compression ratios and share basic driveline components. However, in many important respects the SR500E engine is a creature unto itself.

The SR500E cylinder head has larger fins for better heat dissipation compared to the XT; and while Yamaha has not changed cam timing, the inlet and exhaust tracts have been reshaped to get better performance. Most of the work has gone into the inlet side of the engine where the SR has a 34mm Mikuni carburetor feeding a 47mm intake valve, compared to the XT's 32mm carb and 45mm poppet. Further changes in the cylinder head include new valve-seat material to improve the durability of the seat when using low-lead or non-leaded gasoline, and the exhaust valve guide has been standardized with the intake guide.

Yamaha has not overlooked the piston. The pin-boss area of the 500's piston has been strengthened, the overall length of the piston has been increased by six millimeters, and Yamaha has modified the piston's oil ring. Street riders probably use more revs over longer time periods with less maintenance than their dirt-riding counterparts, and Yamaha has made all these modifications to guard against excessive oil consumption.

Downstairs in the crankshaft department, Yamaha increased the flywheel capacity by extending the diameter of the crank webs, claiming a benefit in reduced mechanical noise. Moreover, the material in the forged and hardened crankshaft was changed in the redesign.

Cost and appearance considerations probably led to the disappearance of the magnesium side covers found on the dirt singles. Both the left and right side covers on the SR500E are buffed-out aluminum. Yamaha spent their money in other ways: The SR500E has a hoop around the clutch housing to strengthen this component, detail changes have been made to some transmission gears to increase their durability, and the shift pawl and drum have been modified in order to get easier, more positive shifting. Specifically, the toothed primary pawl, instead of being splined to the shift shaft, is integral with the shaft; now there's nothing to loosen or slip. And the shift drum is supported on the left side by a new needle bearing that reduces drum drag and facilitates smooth gear-changing.

The fussing with the crankshaft assembly suggests Yamaha's concern with vibration, a traditional complaint about the big single. That concern shows elsewhere, but not necessarily in a way the casual observer might expect. The XT has one rubber and three solid mounts that attach the engine to the frame, whereas the SR500E, far from being rubber-mounted all the way round, is solidly fixed to the frame at all four points. Enormous soft-rubber bushings, like the old Norton system, would have isolated the thumping vibrations of the 500 single from its frame. Yamaha rejected this complicated and expensive option. Elaborate soft-mounts or counter-rotating balancers were out of the question too; those solutions violated the simplicity and cost-effectiveness that Yamaha wanted in the SR500E. So the engineers did more homework on frame design and solid engine mounting in order to hold the vibration through the frame to an acceptable level.

Outfitting the 500 for street duty included a new frame. The tubework may be based on the XT500, but frame-tube diameters have been increased and key points of the frame have been reinforced to increase rigidity. A strong and fairly massive frame that clinches the engine tightly can carry off engine vibration without fracturing, transmitting some of the pulsing through the suspension to the ground. To illustrate where vibration can go, step back five feet from an idling SR500E, watch the bike move on its suspension, and then put your hand to the pavement—and feel the quaking.

No wonder that the rear fender, gas tank and footpegs are rubber-mounted. In fact, even the caliper mounts for the rear disc brake have rubber bushes to soften the vibration. The battery-box space has been made large to provide more room so that longitudinal vibrations won't rattle the battery against nearby components.

Incidentally, the side cover and battery box have been designed in such a way that both the battery and tools (under. a lockable cover) can be removed from the left side of the bike, and the air cleaner can be pulled out from the right. Because the under-seat items come out the sides of the motorcycle, the seat is bolted in position. It doesn't lift up on hinges.

Compared to the XT500, the SR500E has considerably less rake (27.7 degrees vs. almost 31 degrees) and trail (4.7 inches vs. 5.7 inches), producing a quicker-steering bike. The front and rear suspension units more nearly resemble the components found on the XS650 than those fitted to the XT500. Indeed, the SR500 has no off-road capability with a front fork that travels only 6.0 inches, whereas the XT is good for 7.8 inches. At the rear, very ordinary oil-damped shocks provide 4.4 inches of rear-wheel travel, while the XT500's forward-cant DeCarbon shocks allow the rear wheel 6.4 inches of movement. The SR500E also has a slightly shorter wheelbase (56.25 inches) than the XT's 57-inch span. Not surprising is the fact that the 383-pound SR-E packs 64 more pounds than the XT.

Some of the extra baggage has gone into the electrical system. The SR500E has 12-volt electrics charged by a multi-pole alternating-current magneto, instead of the XT's six-volt system with a direct-current flywheel magneto. And the breaker-points ignition fitted to the XT500 has not been carried over to the SR-E. The roadster has a magnetically triggered CDI to fire the spark plug.

Yamaha has provided more than an energetic spark-maker in order to persuade the SR500E into life. Obviously an electric starter would contradict the notion of a light-and-lithe, simple-and-direct single-cylinder roadster. In addition to the starting lever, there's plenty of gadgetry. First, one manfully gets the kickstart lever under foot, hopefully under cover of a good boot. Of course Yamaha figured some owners would step to the starting drill with frazzled tennies, and so the company took pains to protect its light-footed Customers from the uplifting and crippling effects of The Dread Single Cylinder's Recoil & Backlash Through The Starting Lever, And Subsequent Catapult Over The Moon. Using the compression release which lifts the exhaust valve, one cranks the works over until a little white arc appears in a tiny window at the right outboard side of the overhead camshaft.

Then one flicks the choke lever, provided that the engine is cold, and pushes the white throttle-set knob, located nearby the choke lever, into its up-position. With the ignition switched on, and with care not to crack the twistgrip open, the rider thrusts the starting lever downward and awaits those comforting ka-thunka/ka-thunka sounds to well up from the engine department. Failing that, one again consults the old peekaboo window, gives a macho ah-what-the-hell-l-was-only-kidding shrug, and continues to kick.

Until our test SR500E was broken in fully, and until we learned not to flood the thing (the Mikuni has an accelerator pump), and until experience demonstrated that the throttle-set knob should be trusted to raise the throttle-slide the exact amount, the SR500E would either start on the first or second kick or not at all. One Cycle staffer (not an editor) managed to kick the Yamaha into a deeper and deeper case of moodiness until at last he was squirting sweat and frustration from every pore in his body, and nearly a gallon of sweat collected behind his jacket's tightly secured wrist cuff, waterlogging his right arm all the way to the elbow. Without so much as a burp of encouragement, the SR-E refused to push/bump start, and the hapless novice only succeeded in leaping aboard from the left side, skidding the rear wheel, and toppling over—bike and all—into a steaming, cursing heap.

The Yamaha never so cursed the life of the editorial staffers, and firing off the SR500E was simple and easy—after learning what to do, and what not to do. In fact, the neatest trick in the whole start-up routine is resetting the start-throttle knob. The rider just rolls the twistgrip back against its fast-idle position, thus returning the throttle-set button to its off-position. Thereafter, the engine always drops down to its 850- 900 rpm slow-idle speed.

Everyone who rode the SR500E agreed: The motorcycle is enormous fun. Not an awesome motorcycle, not dazzling, not brilliant—but fun. Those riders who have grown up on electric-start twins and fours were intrigued by the single-cylinder Yamaha because it represents a different approach to connecting Points A and B on tarmac. The SR500E is a machine of essentials; a responsive, glove-fit motorcycle.

That motorcycling concept may be fun, but in the real world sometimes being fun isn't enough. After all, steam calliopes are fun, Excalibur roadsters are fun, fifty-year-old two-wheeled crocks are fun. But any modern single-cylinder motorcycle must meet the hard test of reality. What can it do? How does it perform? To make sense in a world of thousand-dollar kick-start twins from Honda, Kawasaki, Suzuki and Yamaha, the $1500 SR500E must perform better in some dimensions than the econo-twins. Granted, you can't buy anything like the SR-E from another source; Yamaha has the corner on the 500cc single-cylinder roadster market. Nevertheless, a 50 per cent premium is a lot to pay just to be different.

In functional terms, the SR500E starts with substantial advantages. It is a specialty motorcycle, a fairly narrow-focus machine, and isn't subject to the kinds of compromises that econo-twins must unavoidably make. Consider the simple matter of seating. In order to attract a broad range of customers, the 400 twins must offer reasonably comfortable accommodations for passengers, and this strategy dictates fairly long, heavy, cushy seats. On the other hand, the Yamaha SR500E is basically a monoposto device, scaled to one person.

Yamaha has capitalized on this seeming limitation. In the first place, the distance between the seat and the rider's footpegs is great enough for real leg room: no semi-double-back positioning.►