The Motorbike Archives

At first, speed-struck hotheads had to settle for 250cc TD1 roadracing pistons and barrels bolted to their lumbering YDS3s. Then the R5 arrived in 1970 to quench their passion for faster machinery. It was patterned after the Yamaha 350cc two-strokes that had begun to humiliate four-stroke bikes on roadracing circuits around the world, and for a while it and its RD350/RD400 descendants satisfied hard-core Yamaha speed freaks. But ever since the water-cooled TZ250 hit the track in 1974 followed by the Monoshock TZ of 1976, Yamaha RD riders have fretted over the growing credibility gap between the RD and their roadracing fantasies.

But now at last it's possible once again to buy a piece of Yamaha's roadracing action—the RD350LC, a Monoshock, liquid-cooled (LC) example of race-wise technological trickledown. It has become one of the most lusted-after motorcycles of 1980, the ideal street-racer for legions of RD disciples, a TZ with lights. Even though nearly nine months elapsed between the bike's introduction and the arrival of the first production units, 10,000 examples already have been sold in Europe alone.

You can't buy the RD350LC or its little brother, the RD250LC, from your local Yamaha dealer, though. The explanation can be found in EPA air-emissions regulations and Yamaha's market-think for the Eighties. But even so, private individuals have begun importing RD350LCs. And indeed, CYCLE GUIDE went to the same trouble (see page 40). Even if the LC was to be limited to a very exclusive audience in the U.S., we figured the ultimate two-stroke street bike represented an experience that deserved exposure. Frankly, the temptation of getting our hands on a piece of Yamaha's action proved too much. That's how each of us came to find himself peeling off into Willow Springs Raceway's notorious Turn Eight, a long, bumpy, right-hand sweeper, while tapped out in sixth gear on this Monoshocked RD.

And in that instant, we understood why the hassles of importing the LC had been justified. The repli-TZ made the transition into Turn Eight in a single, fluid movement that only a pure-bred high-performance bike could hope to produce. Where the RD400F would have been shaking like a cowardly mongrel at 99 mph, its engine surging and bucking at 7300 rpm, the RD350LC ran straight and true at 110 mph with its belly to the ground like a race bike, its engine begging to be permitted beyond the 9500-rpm redline.

You would expect race-bike finickiness from such a motor, and that's just what you get. Below 6000 rpm, the engine isn't strong enough to pull the wings off of a fruit fly. It tells you of its unhappiness by shaking fitfully in its rubber mounts. A flaw in part-throttle carburetion (it is too rich according to factory spokesmen) makes it all but impossible to accelerate in sixth gear at less than 6000 rpm. It even takes a good deal of delicacy with the clutch just to get the light-flywheel engine away from a dead stop, as a comparison between the LC's dyno curve and that of the RD400F reveals.

You're paid back for this discomfort, though, once the tach needle crosses the 6000-rpm border and the motor begins to accelerate. It finally uncorks at 7500 rpm as port timing, exhaust tuning and carburetion suddenly come together, and the bike leaps forward with a terrific rush. In the past, two-stroke street bikes were calibrated so that port timing, exhaust tuning and carburation affected different areas of the powerband, providing a broad spread of less-than-optimum power. The LC, on the other hand, has been tuned to provide its power all at once, like a race bike.

Power like this might lead you to expect a watered-down TZ race engine in workaday harness. But what you get is something of a water-cooled RD350 street engine. It shares the same familial resemblance to racing engines that all RD engines have, but it is not a TZ replica.

The LC's bore and stroke reproduce the old RD350's dimensions, while the separate cylinder barrels and one-piece cylinder head incorporate lessons learned with the RD400. Yet the LC's two-ring pistons and built-up roller-bearing crankshaft do not mean the LC's engine is interchangeable with previous RD's. The motor uses technology gleaned from the TZ in its bottom end. To begin with, the crankpins are integral with the outer flywheels. The inner flywheels are pressed over them, lending the lightweight crank more rigidity. Also, the cases use locating pins to keep the main bearings from spinning. Both of these features prolong crankshaft life in a high-output two-stroke engine. A close-ratio transmission, designed to cope with a narrow, muscle-bound powerband, does the job of transmitting the horsepower.

Though the LC engine isn't exactly a clone of a TZ powerplant, its radiator is more than window-dressing. When you consider that 80 percent of the heat produced by a two-stroke engine is dissipated through the cylinder head and most of the rest through the area around the exhaust port, you begin to understand how liquid cooling can reduce metal distortion and so permit high specific output without risking piston seizure. The LC employs an impeller pump to draw coolant down from the frame-tube-mounted radiator and then pump it through the barrels, into the cylinder head and finally back into the radiator. A plastic helical gear located just above the oil injection pump and driven by the primary gear powers the impeller. The cooling system holds 1800cc of coolant and its overflow tank is mounted aft of the injector oil reservoir beneath the right side-cover. Since there's no thermostat in the LC's watercooling system, there's no telling what the bike might be like while trapped in a mid-summer traffic jam, but it did the job on the racetrack.

Just as the engine reveals lessons learned from the TZ hardware, so too the chassis employs TZ-think if not actual TZ pieces. In broad outline, the LC frame and early Monoshock TZ frames look the same in terms of layout. Unlike the race bike though, the RD's nitrogen-charged Monoshock is foreshortened like that of a TT250, and only its spring preload is adjustable.

Compared to previous RD frames, the LC's chassis is just an inch longer and uses fractionally quicker steering geometry, yet the difference between the chassis of the RD350LC and that of an RD400F is nothing less than astounding. For all its merits as a boy-racer, the RD400 combined hair-trigger steering with a soft suspension meant for freeway riding. A series of bumps at speed would unleash a diabolical wiggle from the rear end as the short-lived shocks worked against a flexible swingarm. In contrast, the LC chassis just hugs the ground while going around a corner. The Monoshock's impact on swingarm flex and rear-wheel deflection apparently is just as significant on a street bike as on a dirt bike. The RD350LC still steers with the same quickness Yamahas are noted for, but the slightly longer wheelbase and Monoshock rear suspension keep it from darting around like an RD400. The slightly higher cg imposed by the Monoshock also lends the bike a further measure of stability.

Suspension rates play a significant role in the LC's high-speed personality, as well. Occasionally, the Monoshock will prove a little short on rebound damping even for 160-pound riders, yet the damping is otherwise fairly firm, recalling an RD350 rather than the mushy RD400. The fork feels resilient but firm in much the same way. Naturally, this means you can expect a measure of harshness, especially in response to abrupt inputs.

When it comes to detailing, the LC's riding position produces the magic mean between braced and crouched, just like the Euro-XJ650 tested last month. The shape of the seat lets you move around on the bike with the effortlessness of Kenny Roberts. The gearshift linkage proves a little notchy and it's almost impossible to locate neutral because of the gearbox's weak de-tents. The powerful but progressive dual-disc front brake is capable of standing the bike on its nose without locking the front tire, making the rear brake largely ornamental. Only the Yokohama tires fail to live up to the TZ image. They skitter and slide long before the centerstand comes close to scraping the pavement.

Once you cut to the quick of the RD350LC's personality, you have to admit it's probably not the perfect motorcycle for everyday use. As one Yamaha spokesman commented, it's built for people who appreciate two-stroke power—and that means a kind of exaggerated peakiness that's supposed to be synonomous with high performance. Make a mistake while riding into a corner and you must downshift at least twice to regain your momentum. And after about 30 minutes, the handlebar gets very tingly and the suspension's harshness becomes apparent. Then there's the fact that the engine refuses to cruise at 60 mph in anything taller than third gear. Also, you have to fold up the right footpeg before you can kick the engine over. The RD350LC is simply too much like a race bike to please very many people as everyday transportation.

Yet at the same time, the LC offers race-bike virtues that express perfectly what we mean when we say high performance. When you strafe an apex on the LC, both ends of the motorcycle work together in a balanced way no previous RD could ever duplicate. Transitions are so easy you'll think you have the talent of a GP rider. Every move the LC's chassis makes is crisp, sure and confidence-inspiring. It's immensely satisfying to skewer an apex with a rapier-like thrust instead of thrashing away with some unwieldy cutlass of a hyperbike.

This is the quality CG's riders have longed for ever since we saw one of the first matte-black LC prototypes slip out of Yamaha's Iwata R&D facility headed toward the Yamaha test course—one of the most demanding roadracing tracks in the world. Even though the LC owes as much to previous RDs as to the TZ racers, the LC lives up to this promise of raceworthiness. As one of the reference points when highspeed handling is discussed, it reminds us of the benefits to be derived from bikes with light weight and lower center of gravity than the average DOHC four-stroke.

It might be true that the two-stroke street bike is irrevocably gone from the shores of America. It could be that Europe and Japan understand the language of the two-stroke better than we can. Even so, the LC proves that the RD-series should be perpetuated in this country in chassis if not in engine. Because as long as Yamaha builds roadracing bikes, there will be hard-core sporting riders who demand a piece of the action. The RD350LC gives it to them, and in a language that everyone—not just two-stroke devotees—can understand.

RIDE REVIEW

A world without water-cooled RDs would be noticeably duller, a few steps closer to living in shades of tan and gray. No other motorcycle allows you to so nearly reproduce the sensations of a full-on road-racer while still dangling the carrot of street legality—at least in some more-civilized countries. I'm fascinated with the RD's roadracy kinesthetics—incredible lean angles, smooth, faultless braking and the letter-perfect riding position—but that doesn't mean that I'd want it on the street. Racers belong on the racetrack, even thinly disguised racers like the RD. Coaxing one through slow-moving traffic would be hell. The powerband is thinner than a bureaucrat's promise; fall off the 7000-rpm ledge and you need serious gearbox rowing to keep moving. It's just too much effort to be fun. So give me an LC, Yamaha, but let me keep it at the track. —Larry Works

The first lap around Willow Springs told the story: The RD350 L/C is nothing more than a race bike. It has the same basic powerband as my old—and incredibly fast, thanks to some magical porting—air-cooled RD350 racer. The suspension is taut, and when you point the front wheel into a turn it goes exactly where you want it.

Port specs and trick suspension aside, the true measure of a racer is how quickly it circles the course. And here, the stopwatch is the final authority. My best L/C time would have put me in the top 10 of an AFM 43Occ production sprint. What slowed me down during our testing was that the stock Yokohama tires slip and slide through turns. Give me a set of good treads, and I could stop the clock at trophy-winning time. That's what I appreciate about the L/C—it's race-ready with just good tires and fresh plugs.—Dain Gingerelli

The RD35OLC could bankrupt me. It wouldn't be expensive to buy, but I don't think I could afford the speeding tickets. The little waterpumper doesn't have the sheer speed potential of a CBX or GS1100, true, but it will still exceed twice the legal maximum speed limit.

What is important is that it almost demands to be ridden at those speeds. It does more than look like a TZ roadracer, it performs more like a racer than any other street motorcycle I've ever ridden. That means narrow powerbands, high revs and not a little clutch slipping.

All of which adds up to a pretty unpleasant street motorcycle. But who cares? This is the world's best repli-racer and I loved every high-revved moment aboard it. The price of owning one wouldn't be too high if only I could get a season speeding ticket.—David Dewhurst■

THE SHOCKING QUESTION

Why bother with a Monoshock on a street bike? Well perhaps you should ask why we ever bothered with twin-shock systems. You see Monoshock, or more precisely monospring, was the basis for some of the earliest motorcycle rear suspensions. In 1919 the Beardmore Precision was lifted above the rigid-frame crowd by a triangulated rear end and a single leaf spring. HRD Vincents were similarly blessed in the late Twenties.

So why did we bother with twin shocks? An answer is difficult to justify because a Monoshock rear suspension really does have many advantages. Not least of which is the increased rigidity of the swingarm. The tube layout designed to support the lower shock mount also triangulates the swing-arm in two planes, which helps keep the axle and chassis running in the same direction.

A similar advantage also comes from using just one shock. If it should fade, both sides of the swingarm are affected equally. That is not always the case with slightly mismatched twin shocks that can allow both sides of the swingarm to react at different speeds, causing flex. One disadvantage can be the slightly heavier weight of a single shock system. But while high unsprung weight is a definite disadvantage, a slightly high center of gravity can also be beneficial. It helps straight-line stability while trading just a little cornering agility.

There are major difficulties with Mono-shock, but they mainly concern the designer. He has to find locations for the many parts displaced by the shock. On the Yamaha, the shock passes right through the air box space under the seat. That is why the RD350 has a pancake filter far under the tank and a complicated connection with the carb bellmouths. The airfilter in turn takes up valuable gas tank space, which might account for the rather bulbous outer dimensions of the tank.

Adjustments to the shock are also difficult to make on the RD350, requiring re- moval of the seat for spring preload changes. But as Yamaha has shown with its dirt bikes and even the latest vee-twins, Monoshocks can be made simple to adjust.

When adjustable with a single flick of a gloved wrist, Monoshocks really do have few things going against them. The deciding factor is the ability of the designer to integrate the concept into his motorcycle. As the RD350LC shows, the benefits are many, but so are the problems.—David Dewhurst