Roberts racing machine

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Roberts racing machine

Roberts racing machine
Formula three

Are three cylinders enough to win a 500cc Grand Prix? Old master Kenny Roberts says yes – and sends his son Kenny jr. and the Frenchman Jean-Michel Bayle with the Modenas KR 3 in the ring.

Manuel Pecino


At the start of the season on 13. April in Malaysia, the eyes of the Grand Prix world will mainly be on a motorcycle. “Modenas KR 3” is the name of the new 500 series racer that arouses curiosity in the scene. Not only the technical concept is interesting, but also the people behind the project: a half-liter machine with a V3 engine, designed and built by the team of three-time world champion Kenny Roberts and the English Formula 1 forge Tom Walkinshaw Racing (TWR). Marlboro and the Malaysian motorcycle manufacturer Modenas are providing the financing.
Although the first cautious test rounds have just been completed in Barcelona, ​​Roberts is already expecting podium places or even victories in the premier class for the first season. Kenny Roberts junior and Jean-Michel Bayle should reap the laurels – two drivers who, however, do not belong to the first guard of the 500 pilots. Doubts about the optimistic forecasts are therefore justified. Nevertheless, King Kenny deserves great respect for his courage to interfere with a new variant in the competition of engine concepts – so far the V4 fought against V2.
The great master has not yet been able to elicit measured values ​​or even dimensions of the diaphragm-controlled V3 engine. Except for the fact that he has exhausted the capacity limit and the central cylinder of the engine is upright and tilted slightly forward. In order to ensure that the center of gravity is as low as possible, the two outer cylinders in the V spread downwards. The associated exhaust systems are also routed along the underside of the engine. The only disadvantage: The two outer cylinders on the underside of the machine also ensure a construction width that almost corresponds to the common V4 models.
Kenny admits that the first stage engine was built very conventionally. In order to avoid teething problems and to be able to ride right from the start, the crankcase was made of aluminum and exotic materials were avoided. »After the first test bench run, we already started to further develop the engine housing. We are working on parts that are as small and light as possible. We’re also modifying the water pump to improve cooling. “
While the new parts are being built in Roberts’ workshop in Banbury, UK, and at Tom Walkinshaw Racing, the drivers are testing with the first version of the KR 3. For Kenny junior, the V3 racer seems – who is surprised – to be almost tailor-made. “The engine has a great power curve, I like that. I can control the machine well with the rear wheel, almost like a flat-track motorcycle, “said old master Kenny’s offspring, summarizing his first impressions of driving on the Grand Prix circuit in Barcelona.
Revolutionary innovations are not to be expected on the KR 3 before the start of the season, at most a slight pound cut through the use of titanium, carbon fiber and several magnesium parts. “But none of it is spectacular,” says Roberts. “We didn’t try to reinvent the wheel.”
The greatest curiosity is likely to arouse the carburetors, which were completely redeveloped in the Roberts factory. How effective they are will be shown by the performance of the machine. The team is currently talking about 150 hp, but in order to be competitive, the KR 3 still has to gain a lot of muscle. Roberts has already mentioned several times that you need 165 hp to be able to show it to the V4 machines that are around 30 hp more powerful, but also 15 kilograms heavier.
However, the Swiss Grand Prix technician Urs Wenger does not really want to believe that this project can be realized. The designer of the Swissauto four-cylinder defends the V4 concept as the only one that really promises success. “Roberts ?? V3 machine should behave like a particularly good twin because it combines the concept of a compact machine with greater power. But it remains inferior to the four-cylinder because it will never achieve a comparable performance. Personally, I consider the three-cylinder to be the most difficult of all possible concepts. With a twin that, according to the regulations, only has to weigh at least 100 kilograms, you have at least the guarantee of being as fast as a 250 and scurrying away from the 500 on certain routes. But with a V3 engine weighing 115 kilograms, you have clearly less power than a four-cylinder and still not have the advantages of a V2. “
The Spaniard Antonio Cobas, inventor of today’s widespread aluminum delta box frame and designer of the JJ Cobas 125 with which Alex Criville became world champion in 1989, does not take a clear position. “I hope and wish that the machine works,” smiles the man who, years before the first V2-500, was absolutely convinced that the ideal racing machine had to be somewhere between a 250 and a 500. »I like the idea, even if it is difficult to give a judgment without detailed knowledge. But when you realize that Roberts and important Formula 1 figures are behind the project, the prospects are by no means bad, ”calculates Cobas.

Three-cylinder in Grand Prix racing

Three-cylinder engines are by no means new to the half-liter class. It all started with the three-cylinder four-stroke engine from MV Agusta in the mid-1960s. Multi-world champion Giacomo Agostini hurried from victory to victory with the superior in-line engine. In the shadow of the great MV Agusta factory machines stood the Kawasaki two-stroke engines with three air-cooled cylinders in a row that were introduced at the end of the 1960s. After all, Ginger Molloy won the runner-up title in 1970. The Honda NS 500 was of a completely different caliber. At the beginning of the 1980s, when the competition consistently relied on Square Four engines with rotary valve intake and Yamaha had just started to design a new V4 machine with two crankshafts, the world’s largest motorcycle manufacturer went with them a sensational V3 machine with a 100 degree cylinder angle and membrane inlets into battle. As early as 1983, the exceptional American driver Freddie Spencer and the 140 hp NS 500 were mature enough to snatch the world title from Roberts. Until 1985, the NS 500 was still on the starting line as the official factory machine, but in the meantime it had lost ground drastically compared to the strongly further developed V4 machines from Yamaha. For private drivers, however, the Honda RS 500 Production Racer was still an attractive racing machine well into the 1990s. Honda built the engine with two upright and one horizontal cylinders – like DKW in 1953, whose 350 series was equipped with the first three-cylinder two-stroke engine in racing history .

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