The Dakar Rally, which is currently staged on the South American continent, was previously held on the African continent as the Paris to Dakar Rally (Paris-Dakar) from its first year in 1979 until 2008.
The founder of the Paris-Dakar was a Frenchman named Thierry Sabine who had raced in rallies in Africa. Sabine also raced in the first Paris-Dakar (called the “Oasis Rally” at the time) that he organized himself. Many participants of the early rallies were French, reflecting a national preference for long-distance endurance races.
At the time, racers in the Paris-Dakar left Paris, France on Christmas Day and covered 12,000 km (later extended) over approximately 20 days. Most of the course was set in harsh conditions including the uninhabitable Mauritanian desert and the Tenere Desert, which is barren in all directions for hundreds of kilometers.
As a result, more than half of the participants would retire from the rally and some racers even lost their lives. Sometimes they even had to cross politically unstable regions, which was the reason why the rally was, both in name and reality, “The World’s Toughest Motor Race” from its very beginning.
Eventually, the Paris-Dakar came to be known widely in Europe as a motor sport event that marked the beginning of the new year. Particularly in France, it became a popular event comparable to the World GP (currently known as the MotoGP) and the 24 Heures du Mans.
At the same time, an increasing number of automobile and motorcycle manufacturers around the world came to participate in the rally in order to promote the performance and presence of their products.
In the motorcycle Moto class, the Yamaha XT500 won two years in a row from the first rally, after which the BMW R80 claimed one victory. Honda made its first appearance in the third rally, held in 1981. At the request of Honda France, the XR500R (550cc) was entered into the rally with the help of the Asaka R&D Center (currently the Motorcycle R&D Center). Although it finished in 6th place that year, Honda achieved four consecutive victories from the next year, 1982.
It was French racer, Cyril Neveu, who drove this machine to victory. Neveu was also the leading rider for Yamaha’s two wins and was an outstanding presence in desert motorcycle riding.
However, even Neveu’s riding was no match for the production motorcycle entered by BMW the following year. The power of the 800cc flat-twin engine was far superior to the single cylinder engines that were mainstream at the time and, despite its weight, its body layout with a lower center of gravity also gave it an advantage.
BMW’s powerful lineup, which included Neveu’s rival, African-born Frenchman Hubert Auriol (disqualified for arriving too early in the second rally) and former World GP Motocross champion, Gaston Rahier, achieved the spectacular feat of three consecutive victories from the 5th to 7th rallies.
Thus, BMW realized an overwhelming winning percentage of four victories in the seven rallies up until 1985. In contrast, the Honda France Paris-Dakar team was simply unable to beat the BMW’s high-speed machine and also played second fiddle to the Cagiva’s machine with an L twin cylinder which made it first appearance in 1985.
In this way the Paris-Dakar entered into the high-speed age. While slightly heavier than single cylinders, twin cylinder machines could quickly reach maximum speed, leading to the evolution of high-speed racing. The rally itself also shifted from a competition mainly for amateur riders to battles between factory teams “going in for the win.”
Of course, Honda was the strongest contender for defeating BMW. At the compelling request of Honda France, the HRC Project Team was formed in the autumn of 1984 and, with the aim of “winning the 8th rally in 1986,” the development of a machine exclusively for the Paris-Dakar was initiated.
The development team mustered up the best and the brightest talents with experience in road, motocross, endurance and dirt track racing. It could be said that with their visit to the 7th rally in 1985, Honda got a true picture of the Paris-Dakar for the first time.
With driving conditions including desert, rocky stretches, loose gravel dirt, savannah and paved roads, temperatures ranged from below freezing point to 50℃. The longest driving distance per day was 800 km in SS (competition section) with additional distances in the liaison route (untimed section). In most cases, gasoline contained dirt and impurities with unstable octane value.
The development team could not hide their surprise at the reality of the highly demanding conditions for which they had to deliver the highest performance as well as durability and serviceability. The requirements for (or the concept behind) a machine that could aim to win under these conditions were as follows.
1) Light-weight and compact (affect all elements including driving performance, rider’s fatigue and durability)
2) Maximum speed of 180 km/h (cruising speed of approximately 150 km/h)
3) Does not fatigue riders (riders demand for flat output characteristics in particular)
4) Does not break down (machine trouble can be life-threatening to riders)
5) Good serviceability (ideally no maintenance needed)
6) Focus on high-speed stability (high-speed cruising in the desert is critical to win)
7) Fuel efficient (Target is 9.1 km/L at the time of design. As a rule, 450 km without refueling (+ 20%))
8) Concentrated mass (concentrated as close to the vehicle’s center of gravity as possible)
Specifically, it was demanded that the engine have flat output characteristics of 3,000-8,000 rpm with high-power and torque with minimum durability of 4,000 km (at the time, a total of three engines could be used.) As a result, the V twin engine with V-bank 45-degree angle and 90-degree angle crankshaft was selected.
This layout can cancel primary vibration, and has an advantage in ease of use, rider’s fatigue, and durability. The concept was based on the expertise gained from the dirt track-specialized machine RS750D V twin engine (same specifications), which was developed slightly earlier.
Moreover, the engine was as slim as a single cylinder engine, leading to advantages in the body layout as well. In order to exploit these characteristics, a unique design was adopted for the machine specialized for the Paris-Dakar. This involved the combination of a needle roller bearing with the monolithic crankshaft to minimize side width.
A connecting rod with a partitioned large end is used for the monolithic crankshaft. Normally, plain metal is used for this section. This is because the bolted part tends to lose precision (roundness) in the assembled area.
However, if one is hoping to use a machine in the Paris-Dakar, it is best to use needle roller bearing, which is strong against momentary oil shortage caused by body inclination and entry of dust.
As this requires that roundness of the large end be secured, the so-called fracture split connecting rod (monolithic molded connecting rod is split apart) was used, making precision in the assembled area possible (this was used in entries after the NR500). As a result, engine oil capacity itself was also able to be controlled.
The water-cooling SOHC4 bulb and V-type twin cylinder engine that was finally completed had bore/stroke of 83 × 72 mm = 779.1 cc and maximum output of approximately 70ps/7000 rpm. The body that this was fitted to was also of a novel and creative structure.
It could be said that the now universal large cowling and big tanks of big off-road models were embodied in this machine for the first time.
The giant split fuel tanks on the left and right were installed down to the sides of the engine in order to lower the machine’s center of gravity. The monocoque below the sheet was also utilized for a gas tank, securing a total capacity of 59 L.
Each of these three tanks had independent oil feeding systems, so the motorcycle could still run even if one tank was experiencing trouble. The tank under the sheet was a rubber Gas Pack and the left and right tanks were made from Kevlar (aramid resin) on the outer sides, which also offered protection from damage or fuel leakage caused by falls.
Apart from this, the machine had an extremely orthodox structure with a steel pipe frame, stroke 280 mm front fork and rear Pro-Line, kick and cell starter and chain drive (large jumps were impossible with a shaft drive), which secured superior serviceability while thoroughly eliminating risks.
The machine, which was based on reliability and ease-of-use rather than extremely-tuned driving performance, showed that it had been completed in line with its concept in the local test runs in the Tenere Desert and other areas. It was named the NXR (the French called it the “neuksar”) and sent to France in order to appear at the 8th Paris-Dakar in 1986 as planned.
Shortly after that, the spare engine in Japan suddenly experienced a problem, with the stud bolts being blown off. The crank case had been made of magnesium alloy in order to reduce weight and it appeared that the parts where the bolts were mounted were not strong enough.
A new aluminum alloy crank case was hurriedly built and flown over to France. This turned out to be the only instance of unanticipated trouble.