Who remembers Honda’s NR500, the oval-piston V-4 four-stroke whose intensive and dear five-year improvement was meant to cease the two-stroke tide in FIM Grand Prix roadracing? Many extra keep in mind American Freddie Spencer (1983, 1985) and Australian Mick Doohan (1993–1997) later dominating Grand Prix bike racing on Honda two-strokes. What unseen drive may have triggered such a change by an organization so publicly dedicated to the four-stroke precept?
Look even additional again, to the interval 1959–1967, when Honda established its identify worldwide by successful 16 world roadracing championships. Its instruments had been daringly designed multicylinder four-strokes from 50cc to 350cc, some revving as excessive as 21,500 rpm. At the top of 1967, Honda stopped racing. Its signature megaphone exhausts went silent as the corporate devoted all its R&D assets to coming into the auto enterprise (resoundingly, with the Civic of 1972).
Through the next decade, Honda assumed the function of “the General Motors of motorcycling,” rising so large and so profitable that it had nothing extra to show.
That ended when Honda’s new president, Kiyoshi Kawashima, selected the event of the CBX 1000 launch in October 1977 to announce Honda’s imminent return to Grand Prix bike racing.
How To Defeat the Two-Stroke?
How would Honda overcome the dominant two-strokes, even because the final four-stroke holdout, the Italian MV Agusta crew, was giving up the combat? MV had been the architect of 38 world titles, 18 of them in 500, the category Honda had by no means received.
Honda’s mission was given the identify NR 500—NR for “New Racer.” A particular group, NR Block, was created inside Honda’s Asaka R&D Center. Famous names led the mission; Shoichiro Irimajiri, whose designs had received Honda’s final Sixties championships, was general chief. Engine chief was Suguru Kanazawa, chassis chief Satoru Horiike—each later rose to directorships of HRC. And a forged of a whole lot.
The three main determinants of engine energy are displacement, rpm, and internet, stroke-averaged combustion stress. Because the final is proscribed by atmospheric stress, and engine displacement is fastened by rule (500cc, or 30.5ci), that left rpm as the trail to aggressive energy—because it had been in Honda’s Sixties racing. That path seemed to be blocked by the 500cc class restrict of 4 cylinders (in any other case the corporate would have instantly begun improvement of a V-8).
Inspiration Strikes
The official story is that one night, Irimajiri was commuting dwelling, questioning why pistons needed to be spherical. If they could possibly be made oval and nonetheless seal, many extra valves could possibly be fitted, in a position to provide fuel-air combination at fabulous rpm. This can be equal to a 500cc V-8 whose pistons had fused collectively in pairs, assuming oval type. It was proposed that such an engine may make 130 ps at 23,000 rpm (ps was metric horsepower, now changed by kilowatts in European energy measurement).
The first step was to check the sealing skill of oval pistons and rings. A easy four-valve take a look at engine, designated Koo, was improvised from an XL250 backside finish. Methods of producing the bizarre components needed to be devised. Upon meeting and take a look at in April 1978, this single validated the idea, however making solely 10 hp.
Next got here a devoted take a look at engine. Koo employed two connecting rods to higher distribute acceleration hundreds into its single broad piston. It can be topped with the deliberate eight-valve head.
In improvement they encountered mysterious “missing piston events” when the take a look at engine stopped operating and its head was eliminated, simply the 2 naked con-rods had been seen. Where was the piston? In NR testing, cyclic crank twist above 10,000 rpm had brought about piston tilting and subsequent breakage.
By October—six intensive months later—this engine had been developed to succeed in 15,000 rpm, making 20 hp. Problems confirmed up as revs rose: lack of ring seal at 10,000, valve spring failures at 12,000. To every drawback had been hooked up engineers and technicians, devising, testing, and constructing doable options—a number of them.
The First Engine
In November 1978, outcomes justified making an attempt a full V-4 construct. For this work the design crew remoted itself in a closed-for-the-season lodge, 115 miles away up within the Nasu highlands. One of the numerous NR engineers, Toshimitsu Yoshimura, recalled that “…we wrapped ourselves in blankets as we drew layouts, because the heat wasn’t working. I recall our excitement at finally having completed the drawings.”
By April of 1979 the outcome, referred to as “0X,” was making 90 ps (88.7 hp) on the dyno. The subsequent, and intensely bold, objective was to check full bikes towards the two-strokes in a number of precise GPs that 12 months.
The pressed-together and closely counterweighted crankshaft and its eight one-piece connecting rods turned on needle rollers, simply as in so lots of Honda’s Sixties GP winners. The entrance cylinder financial institution was offset to the left, and the cylinder Vee angle was 100 levels to offer room for 4 flat-slide carburetors, every with two 30mm throats. The cam drive was at one finish of the crank. Bore and stroke had been (93.4 x 41) x 36mm (36mm = 1.417 inches). A spherical piston of the identical space would have a 66.5mm diameter.
Would magnesium pistons work? Weighing solely 60 p.c as a lot as aluminum, they may cut back bearing hundreds. Nope, they broke up at 17,000 rpm. How about two-piece piston rings, made within the type of J-shaped parts? Kanazawa finally overcame poor sealing (smoke!) by altering piston form from flat faces joined by semi-circular ends, to a more-nearly-elliptical part with steady curvature. It is the flat-faced kind that may be seen in Honda’s museum at Motegi.
Meanwhile, the bike to hold this engine was equally heavy with innovation, having a skinny aluminum monocoque chassis, an inverted Showa fork, carbon brakes, and side-mounted radiators. Many manufacturing bikes right now share applied sciences initially developed for NR500.
First Test
First observe take a look at was at Yatabe Proving Ground in May 1979. Problems appeared, not seen on the dyno, reminiscent of breakage of the cam drive gear practice. This is the “measles” of younger race engines. Crankshafts can not rotate easily as a result of they’re pushed by combustion thumps, whereas the camshafts are both slowing as they carry valves towards their springs or galloping forward, pushed by spring enlargement throughout closing. These “force lumps” can add as much as peak torques many instances larger than estimated by calculation. Development of a compliant aspect to guard the cam drive took time and testing earlier than the breakages ceased. Another drawback was insufficient cooling with the NR’s twin side-mounted radiators.
Back to Yatabe a month later, that they had 105 ps (103.7 hp) and a weight of 276 kilos. This time the prizes had been oil leakage, valve failure, and piston breakup. Frantic redesign and unrelenting stress on suppliers steadily trampled issues to dying.
At the following take a look at at Suzuka Circuit, rider Takazumi Katayama discovered that really feel was no substitute for the tachometer’s recommendation. He, having received the 1977 350 championship on a Yamaha, was used to two-strokes, whose steep energy drop-off after peak energy indicators when to upshift. The NR simply revved, giving no tactile warning as its tach swept into the crimson zone, scattering an engine.
The Honda NR500’s First Race
June and July 1979 had been stable with testing and trampling. The objective of all this sleepless effort was the deadline for transport accomplished NRs to England for the British GP at Silverstone. With 0X engines, the bikes had been run in Silverstone free follow by riders Mick Grant and Katayama.
Despite issues crushed, the bikes weren’t able to race. As the GP annual Motocourse put it that 12 months, “…they sounded fascinating and had the look of extremely intelligent engineering, but they simply got in the way. They were slow down the straight and slow around the corners.”
Yet the crew had arrived with all the trimmings of success: large transporters, hospitality tents, and teeming personnel. It was most humiliation. Grant’s bike was gradual to push-start (operating engine begins weren’t adopted till mid-1984), it tipped over on the first nook, and burned. Katayama was shortly out as properly.
Grant later revealed, “They didn’t want me and Katayama coming last and second-to-last so they told us they only put in enough fuel for a few laps, and to put on a show, then stop.”
Problems Continue
The French GP was worse: Both NRs did not qualify. Despite this, the crew rolled them onto the beginning grid, filling the positions of two qualifiers who had in some way disappeared. Race officers ordered them eliminated.
After this they examined at Donington with rider Ron Haslam, figuring out wanted enhancements. Engine response was jerky, slowing nook exits. The trigger? The effort required at roll-on to unstick the eight throttles from the closed place the place the engine vacuum was firmly holding them. Mechanics referred to as this “the bang.” Differently formed throttle pulleys had been examined, growing mechanical benefit at the start of throttle slide carry.
The NR additionally shared an issue that had hindered the MV fours towards the top: engine-braking on closed throttle was dragging or hopping the rear wheel, interfering with braking and nook entry. For this they created the slipper clutch, discovered on so many bikes right now. When the rider closes the throttle from excessive revs, the rear wheel drives the engine. Ramps constructed into the drive utilized this reverse torque to cut back stress on the clutch plate stack, permitting it to slide, stopping the hop. The slipper’s second software can be the particular 1,000cc V-4 bike referred to as “FWS,” designed particularly to win Daytona (it led repeatedly however ate its tires).
Continual Refinement
In November, the following NR model, 1X, entered the format stage. Its weight grew from measures vital to enhance reliability over 0X.
In April of 1980 it was clear the monocoque chassis made engine entry too gradual for the tempo of a racing weekend. This was regardless of Honda’s particular NR service trolleys, one for the engine and rear wheel, the opposite for the chassis and entrance finish. After eradicating the numerous 6mm screws becoming a member of the 2, they could possibly be rolled aside for such routine actions as spark-plug entry and carburetor jetting. Too gradual. A standard steel-tube chassis was designed by Ron Williams to offer regular service entry and lift stiffness. This English chassis would have a traditional front-mounted radiator and single unit rear suspension.
Development of the 0X continued, reaching 115 ps at 17,500 rpm.
By January 1980 the 1X model had reached 120 ps at 18,000 rpm, now with a central cam drive gear practice and a 90-degree Vee angle, made doable by engineering extra compact carburetors. Weight had risen to 320 kilos.
In October 1980, format of a 2X model of the NR engine started. Think of the foundry rush jobs, pouring aluminum and magnesium, the high-priority machining, the standard management measures.
Near the top of 1980 Mr. Irimajiri acquired a proposal from engineer Shin’ichi Miyakoshi, then growing two-stroke motocross engines in MX Block. His concept arose from his latest journey to the GP at Assen, the place he observed that race instances of 500s and 250/350s weren’t far aside. What if, he proposed, Honda had been to construct a easy two-stroke idea he referred to as “a 100 hp 250″? Being light, it would accelerate well and be kinder to tires than the high-horsepower four-cylinder two-strokes.
During the 1981 season I would see and hear the NR at Monza, Italy, under the grand old shade trees there. Upon start-up, it sounded exactly like a big muscular Superbike of twice its displacement, deep and powerful. What a contrast on the track and at race revs. It was hard to tell it from Suzuki’s RG500 square-four two-strokes! Why? Because the four-stroke’s peak revs were close to twice those of two-strokes, while the two-strokes fired twice as often per cycle.
Despite Honda’s immense commitment of R&D resources, NR won no races and earned no GP points.
NR work continued—the 2X version reached 125 ps in 1982, and 1983′s 3X variant reached the original goal of 130 ps at more or less 19,000 rpm. Two basic roadblocks remained: Two-stroke power was now rising steeply, and second, the NR was still 60 pounds heavier than its competition. Two-stroke power growth was coming from subtle changes to cylinder ports and exhaust pipe shape, while four-strokes had to raise rpm to boost power—an expensive process.
Honda’s urgent weight reduction program was partly successful, yet the 40 extra pounds of the NR’s machinery-packed cylinder heads remained. Jorg Moller, designer of Franco Morbidelli’s title-winning 125s, said at the time, “Ideas remain important in the design of two-strokes. But for four-strokes, it is only money.”
Extrapolating from the 19,000 rpm Honda had wanted to succeed in 130 ps, the 190 hp of the final two-stroke 500s would have required an NR dependable at 28,000 rpm. Other inconvenient information remained: that friction loss tends to rise in proportion to rpm, squared, and that on the initially deliberate 23,000-rpm most, peak piston acceleration would have been 30 p.c above something then present in F1.
Was the NR a Failure?
The resolution got here on the finish of 1981 to proceed oval-piston analysis whereas racing Miyakoshi’s two-stroke triple. Freddie Spencer as rider can be important. The NS500 was making simply 108 hp when it began in its first GP in 1982, and Spencer was in a position to win the very quick Belgian GP at Spa. With the drive of Honda R&D behind it, the NS was quickly making over 120 hp at 11,000. Freddie rode it to the 1983 500 World Championship. Honda and rider Mick Doohan would experience Honda four-cylinder two-strokes to 5 consecutive 500 titles.
Many years later, engineer Yoshimura was to say, “When I look back…I’m not sure if we were experimenting with cutting-edge technologies or obsessed with foolish ideas.” In his desk at work he stored a small assortment of unique failed components. He mentioned they reminded him of the numerous chilly hours spent within the lifeless of winter at that vacant lodge in Nasu.
Because on the time FIM guidelines permitted supercharged 250s to compete within the 500 class, improvement continued on an oval-piston turbo twin. By October 1984 the turbo mission had reached 153 ps on the dyno. It was by no means raced.
Was NR500 a failure? Judged solely on its said purpose to win the five hundred title, sure.
But when massive numbers of artistic individuals are given freedom and assets to discover in all instructions, helpful innovation outcomes. Not solely had been many ideas originated which might be in broad use right now, however NR gave Honda a brand new route in engine design: the V-4. It was instantly ordered into manufacturing as Magna (1982) and Interceptor (1983), remaining to at the present time a residing engine structure. Think of Bell Labs in its free-wheeling days, leaving researchers alone to observe their pursuits. Who can place a price on their most important outcome: the transistor?
Oval pistons had been banned from Formula 1 use, however Honda did produce some 300 examples of an NR750 manufacturing bike. Like so many limited-production exotics, they had been devoured up by collectors and now repose in temperature- and humidity-controlled rooms.
It’s fascinating to notice that two cylinders from a present-day 1,000cc V-4 MotoGP engine would give slightly below 150 hp at 20,000 rpm with spherical cylinders, 4 valves, and plain bearings. The not possible turns into the doable, and what as soon as appeared magical turns into commonplace.
Source: www.cycleworld.com