The city of Salzburg in Austria is widely regarded as a mecca for music lovers, but what is somewhat less well-known is that it was also the location of a major turning point in the history of motorcycle racing. In the spring of 1982, Yamaha introduced an innovative machine into the premier 500cc class of the Road Racing World Championship Grand Prix.
This groundbreaking motorcycle was the first GP machine to feature a compact V4 engine with a Yamaha-exclusive rotary disc valve layout. The engine was mounted in a frame with a new kind of structural design that would later be dubbed a “Deltabox frame.”
At that time, 500cc World GP machines were capable of top speeds exceeding 290 km/h, but teams were after a technological breakthrough that would allow them to go even faster. The answer Yamaha’s R&D department arrived at was to switch the intake system from using the traditional piston reed valve to a disc valve which would produce advantages at high speed. The engineers began a process of repeated trial and error to find the best solution. The fan-shaped disc turning in sync with the crank to open and close the intake ports allowed the intake timing to be set without having to depend on the piston’s position in the cylinder. This made it easy to attain benefits at high rpm, but also meant that the position of the carburetors on the sides of the engine made the bike too wide overall, and had the negative effect of increasing air resistance.
The search to find a logically sound intake layout continued for days on end. It was then that a young engineer on the team who had been staring at the layout blueprint held up a rotary valve to it and quietly said, “Can’t we put the valve between the cylinder banks?” This would be the spark that started the team on the path to a new layout design. If the rotary valves and carburetors could be positioned between the front two cylinders and rear two cylinders, the engine could be kept to roughly the same width as a 2-cylinder engine (#1). At the same time, a new idea to have the frame wrap around the engine from both sides also came forth.
The new frame featured a triangular (delta) shape—formed by the head pipe itself and the two straight lines running from its upper and lower ends toward the pivot assembly—and its cross-section was in the shape of a box, so its name was derived from those two aspects: “Deltabox.” The head pipe, which bore the weight of the front wheel, and the pivot assembly, which bore the weight of the rear wheel, were connected in a triangular shape. By preserving the engine’s high degree of rigidity, it became possible to use logical means to achieve good overall rigidity balance, and thus bring out quick handling and excellent ride stability (#2).
Yamaha’s GP machine that debuted the next year in 1983 was the first to sport a frame that could be recognized as a Deltabox. Following several improvements, the Deltabox was adapted from the GP machines for use in production models. The TZR250 was released in 1985 as the first production model with a Deltabox frame, and brought with it a style that is said to have later greatly influenced the design of sport motorcycle frames the world over. Today, the Deltabox ideology can be seen in the frames of both MotoGP race bikes and in production models like the R-Series and the MT Series (#3).
In designing the Deltabox structure, there were some unique ideas that never saw the light of day, such as making the frame part of the fuel tank. There was also the pursuit of more freedom to adjust the frame shape to function better as a design element, and innovations in production technology to create more complex shapes in order to meet the requirements for the riding position. But, the immeasurable effort put into developing this “Delta” is what underlies Yamaha’s development ideal of Jin-Ki Kanno.