Honda NR 750 Endurance Racer

so from 1976 on two-strokes prevailed, aided by new noise regulations introduced that year which stifled the four-strokes, Thus when Honda decided to return to GP racing in 1979, after an absence of more than a decade, the engineers had to come up with something very different to be competitive even in the 500 cc category. The result was the NR500, unkindly dubbed the 'Never Ready' by the cynical British press after the new model took a long time to become only Grant gave the new bike an ignominious debut in the 79 British GP at Silverstone: he crashed at the first corner as a result of which the Billion Yen Prototype burst into flames and was burnt out, 

The shame of this long awaited debut forced Honda's team of young engineers, headed by Takeo Fukui, to redouble their efforts, with a reward of partial' success. Os/over the next three seasons, the NR500 gradually evolved into a reliable, if basically uncompetitive, machine in the hands of star riders such as Ron Haslam and Freddie Spencer. Neither was quite able to earn a GP championship point with the bike, but Spencer did win a non-title race in California on it.  The NR500 was remarkable because, in order to be competitive against the two-strokes (which have a power stroke per cylinder for each revolution), Honda needed to build a four-stroke with twice as many cylinders, but a V8 was forbidden  by the FIM rules. Instead, therefore, they designed and built an engine which was effectively a V8, but in the official guise of a V4I

This was achieved through the first-ever use of oval pistons, each fitted with twin conrods, no fewer than eight valves per cylinder, arranged in two rows of four, and twin gear-driven overhead camshafts.  The secret was obviously in the design of the piston rings used to seal the corners of the piston, but naturally whenever the engine was viewed in public, Honda carefully hid the rings from view. They probably had some kind of spring-loaded seal, but that can only be conjecture.

Running at astronomical revs of up to 22 000 rpm, the NR500 was an ultra-sophisticated but ultimately unsuccessful motorcycle: to achieve their coveted first-ever victory in the World 500 cc Championship for riders, Honda had to join everyone else in building a two-stroke - the unusual but this time successful V3 NS500. However, Honda always claimed that the lessons learnt in the course of the NR project were invaluable, and that a design of an oval-piston bike engine could still be perfected. By now, too, Takeo Fukui had risen through the ranks to become one of the top men in HRC, and was still eager to prove the NR's validity.

Accordingly, in 1983/84. Honda developed a 250 cc V-twin turbocharged GP engine, based on the NR concept, with eight valves per cylinder and oval pistons - but this had not been seen in public at the time of writing. This in turn led to the NR750, a normally aspirated 750 cc engine, still with twin conrods, oval pistons, and 32 valves, which made its surprise debut in the 1987 Le Mans 24-hour event, where it qualified second fastest in practice thanks to the skills of Australian Malcolm Campbell, who was riding it in rotation with a pair of journalists. In the race, the Honda prototype stunned onlookers with its speed, before retiring with, according to HRC, a faulty big-end assembly incorrectly tightened.  Producing a phenomenal 165 bhp at 15 500 rpm in 'sprint' form, the new generation oval-piston Honda was detuned slightly for the endurance race.

But even so, 155 bhp at 15 000 rpm in a bike scaling only 158 kg with lights and a generator, practically in road-legal trim, guaranteed scintillating performance and seemed to bear out Fukui's insistence that what had begun as a means of circumventing a restrictive set of regulations, in fact turned out almost by accident to offer a significant improvement.  The reason probably lies in an inherent limitation of poppet-valve engineering: a four-stroke engine is restricted in the power it can produce only by the amount of mixture you can pack into the cylinder, and the speed at which you can get rid of the unbumt exhaust gases after combustion; in other words, flow, which in turn is dictated by valve area. How big the overall valve size can be in turn depends on piston area, and therefore the bore.

Having oval pistons enables more valves to be used, in turn offering greater flow, less reciprocating weight,  higher speeds and more power.  The success of the NR project made it almost certain that an oval-piston road bike would be introduced by Honda before very long - most likely a 250 V-twin, maybe even a turbo! Its launch would give the ultimate justification for Fukui-san's perseverance with a project so many discounted so harshly.

Source of review: Dream Bikes Alan Cathcart

NR 750 reviw

Honda had indeed conquered the World GP with its NS500s, but there were mixed feelings among the project staff. They could not forget the NR500s that had made way for the NS500s as Honda's primary machines in 1982, only to vanish from the World GP in 1983.

Oguma sent in a entry with a new machine to compete in the 24 Hours of Le Mans Endurance Race scheduled to be held in July 1987. Honda's machine was to be the NR750, an NR with increased displacement. The NR750 fared well in the qualifying round, but retired in the final. However, it won the Swan Series race held in Australia that December, blazing past its rivals in a decisive show of prowess. That race marked the final appearance by an NR series machine. Nine years after Honda first began their development under the goal of winning back the glory of the World GP series, the NRs had ended with a glorious victory.

Honda decided to fight for the World GP title with the NR500s, because it looked at the races as nurturing grounds for technology. Although the machines labored for years without a single point, they fostered the talents of numerous engineers and left behind precious assets. Among these were technologies that were later incorporated into production models; bikes that employed many of the weight-reduction techniques their NR ancestors had originated.

Honda introduced the new NR production bike in May 1992, powered by a 750 cc 4-cylinder V-engine with oval pistons. The machine employed an array of cutting-edge technologies, including an inverted front fork, aluminum twin tubular frame, and magnesium wheels. Thus, the NR500s completed their mission with the successful transfer of racing technologies to the production world.

HRC's greatest bikes: The rarest, sexiest V4 of all

MCN By Mat Oxley

Back in the late 1980s Honda made a final bid for racetrack glory with its oval-piston V4 engine. The ultra-rare NR750 racer was built to publicise a new range of road bikes that never made it into production.

as there ever been a race bike rarer than Honda’s NR750? HRC built only two examples of the oval-piston racer, which made the factory’s legendary RVF750 F1 machine and NSR500 Grand Prix bike seem common as muck.

The NR was the most powerful and most technologically advanced four-stroke racer of its time and yet it only contested two events – the 1987 Le Mans 24 hours and the Swann series of the same year – before disappearing from view, never to be seen again, except in Honda’s museum. So, what was Honda thinking? Why did the world’s biggest bike brand spend a fortune creating this astonishing motorcycle, then bury it?

At the time the popular theory went like this: the NR750 existed for one reason: corporate pride. It was designed to save face, to create a happy ending to an earlier story that had ended badly, and to show the rest of the world that Honda was in another world when it came to high-technology. There were also rumours of a road bike, but nothing more than rumours. Back in the late 1970s Honda had re-entered Grand Prix racing after a dozen years out of the sport. By then GPs were entirely dominated by two-strokes, but Honda was a four-stroke company through and through. Building a two-stroke GP bike would have been sacrilege.

The problem was how to overcome the two-stroke’s inherent advantage of twice as many power strokes. Honda’s answer was to dramatically improve the four-stroke’s breathing, by increasing valve area. An oval piston (in fact, an NR piston was shaped more like a tin of Spam) would allow eight valves per cylinder, making a V4 work more like a V8. At least that was the theory. The reality was very different. The NR500 V4 – 32 valves, eight con rods, eight spark plugs and eight throttle bodies – cost Honda vast amounts of money but in three seasons of GP racing it never got close to winning a race, in fact it never even scored a single World Championship point. Over-the-counter Suzuki RG500 two-strokes were faster.
60 hour engine-build

The NR500 was also hideously complex, requiring no less than 60 hours of hard graft to build one engine. At some races Honda employed two shifts of mechanics – one working at the track by day, the other working by night and in secret at a nearby workshop – to keep on top of maintenance. Towards the end of the project Honda were so desperate for success that they took various NR parts to be blessed in a Buddhist shrine. Not surprisingly, the blessing didn’t work. Honda copped a lot of flak for the NR, even though the machine introduced important new technologies to motorcycling – slipper clutches and carbon-fibre parts to name but two. The bike was christened the ‘Nearly Ready’ by onlookers, then the ‘Never Ready’ and was eventually laughed out of the paddock.

Embarrassed by the NR’s failure, Honda went with the two-stroke flow and built the NS500 triple that soon won the company’s first 500 World Championship. The world had moved on and the NR was forgotten as the NS500 and then the NSR500 two-strokes ruled the world. But Honda had not forgotten the NR. The company still believed in the technology and was desperate to prove that the oval-piston concept was a winner.

In the early 1980s Honda bosses convinced the FIM to allow turbocharged 250s into 500 GPs and built an NR250 turbo. HRC squeezed an amazing 150 horsepower out of the little twin, but the engine was a grenade on the dyno and was never even seen by its intended rider, Freddie Spencer. Next, HRC came up with the idea of the NR750 – a 750cc oval-piston V4 in an RVF chassis. Only one problem: a prototype 750 wouldn’t be eligible for many races.
Le Mans

The Le Mans 24 hours was one race where the NR would be welcome, so Honda hired multiple Australian superbike champ Mal Campbell and journalists Gilbert Roy and Ken Nemoto to ride the bike. This was a PR venture to convince people of the viability of the oval piston, not an all-out attempt to win the race and beat Honda’s RVF750-mounted endurance pros.

The NR was mega-fast, making over 150 horsepower in detuned endurance trim, a good 20bhp more than an RVF.

“The bike was a fairly daunting thing because she was a fair step up in horsepower compared to what we were used to,” recalls Campbell, a teak tough Tasmanian who first tested the bike at Australia’s Calder Park two months before Le Mans. “But she was a pretty sweet thing to ride. The power was very linear and the midrange was very, very good – that’s where she was really strong. You’d be a long way out of a corner and she’d start to pull the front up nice and slow as the power came on stronger and stronger. We put a lot of mileage on the thing at Calder, that’s what HRC wanted, plenty of miles.”

Campbell adored the NR because its stonking mid-range made it perfect for the special demands of endurance racing. The unique breathing capabilities of the 32-valve 85-degree V4 gave the bike a powerband twice as wide as other four-stroke racers of the time. The NR produced huge power from 8000 to 15,000rpm which made it easy to ride, even when going off-line to duck past backmarkers. And the flat, linear spread of power gave amazing throttle feel, allowing riders to lay rubber out of every turn. Not only that, the NR was devastatingly fast, fast enough to leave an RVF for dead in a straight-line.
Vindication

While the NR500 had suffered humiliation at the hands of the two-stroke, the 750 seemed to prove that Honda’s oval-piston concept did indeed appear to offer a whole new era of four-stroke performance. Even though Campbell never got a clear lap during Le Mans qualifying, he put the NR second on the grid, just behind Dominique Sarron’s RVF. In the race he got a great start and completed the first hour just behind the Frenchman.

But when the Aussie went out for his second stint, after Roy and Nemoto had ridden their first outings, he knew something wasn’t right. “I came back into the pits because the bike was starting to drag the rear wheel into turns. I told the guys it either had an oil leak or was most probably doing a big end. For some peculiar reason they put in a new tyre and told me to get going, but the engine failed before I’d even got out of pit lane.”

The much-hyped machine was out: swarf had blocked an oil gallery, leading to an engine seizure. It was another huge embarrassment for Honda, especially for project leader Takeo Fukui who had also led the NR500 project. Fukui was an important man and his involvement underlined the significance of the NR project – later he would become president of the entire Honda Motor Company.

“Le Mans was a huge disappointment for Mr Fukui and the rest of the Japanese, especially since everything had gone so well in testing,” adds Campbell. “It was such a huge project and it had been Honda’s dream for many years. They’d tried the NR in all forms and finally they’d come up with the goods, only to be stopped by a bit of swarf.

“According to the miles we’d done in testing the engine was more than capable of doing 24 hours and we would definitely have finished on the podium, barring crashes or whatever. But these things happen…”
16,000rpm, 170bhp

The NR was returned to Japan and everything went quiet again. Then later in the year HRC announced that they would contest Australia’s prestigious Swann Series, with Campbell and team-mate Robbie Scolyer aboard a pair of NRs.

“This time the bikes were going to 16,500, which was a lot of revs in those days,” says Campbell. “And they were making about 170 horse, when the maximum any of the 1000s was making was 145 tops.”

Campbell might have won the Swann if he hadn’t messed up in the first race at Oran Park. “I clipped a ripple strip and put the bike down. I felt pretty guilty about that one.”

HRC suspected that Campbell’s NR had ingested some dirt in the accident so mechanics removed the engine and flew it back to Tokyo, as hand luggage! “They took it back to Japan first thing Monday, rebuilt it and brought it back for first practice at Calder Park on Thursday. They don’t do things like that today – it was serious stuff!”

Campbell won a race at Calder and got a couple of podiums the following weekend at Lakeside, but the Swann title went to an up-and-coming youngster called Kevin Magee riding a factory-powered Yamaha FZR1000. Once again the NR was returned to Japan and once again it all went quiet. And this time it stayed like that, at least for five years before Honda launched the next phase of its oval-piston adventure: the NR750 road bike, a rolling showcase of Honda technology that retailed at £38,000, five times more than a Fireblade. The company was still determined to prove that the NR500 hadn’t been a hugely expensive waste of time.
Lost legacy

The NR road engine was based closely on the racer and had a similarly huge spread of power – 70 per cent of torque available from 7000rpm to the 15,000 red line. The bike was certainly cutting edge, with Honda claiming more than 200 patents, including 50 for the piston rings alone. Getting oval rings to seal properly within the oval bores had always been the biggest challenge throughout the NR project.

Then came the revelation: the real reason for the existence of the NR750 race bike. During the road bike launch Honda announced that the 750 was in fact the first of a whole range of oval-piston street bikes. Next up in the NR programme were a mega-torque large-capacity touring bike and a long-stroke v-twin sports bike, while persistent rumours suggested a single-cylinder on/off-roader would also be on the way. Technophiles the world over licked their lips and waited.

But not one these machines ever made it into production. For once, the world’s biggest motorcycle manufacturer had overstretched itself, its ambition getting ahead of its capabilities. Manufacturing costs of oval-piston engines were prohibitively high and Honda were coming under increasing pressure from rival manufacturers who feared that a technology race might bankrupt the industry. For the same reason oval pistons were banned from just about every type of racing going and it’s still that way today – they aren’t allowed in World Superbike or endurance or in any MotoGP class.

Honda’s radical blue-sky thinking might have made sense in the soaraway 1980s when the world was awash with cash, but the Japanese economic crash of the early 1990s changed everything for the motorcycle industry.

“The 1980s were an unbelievable era,” agrees Campbell. “The factories had money to spend and there was good money to be made wherever you were racing. It’s very different to the way it is now.”

The world has indeed kept on changing. Instead of creating 15,000rpm oval-piston flights of fancy, Honda has spent a long time forging a new way with bikes like the NC700X, a clever, common-sense machine created for a poorer, more pessimistic world. It would be a generation before the advent of the RC213V-S.

Source MCN