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Titanium alloy for forging and pure titanium material for exhaust systems have been developed. The forging alloy will be applied to production of lightweight motorcycle frames and the pure titanium will be applied to improve engine performance. The materials have been made inexpensive by the use of off-grade sponge that includes many impurities for production of titanium ingot. Stable characteristics have been obtained by controlling oxygen equivalent after setting the volume of tolerable impurities by considering mechanical properties and production engineering. In spite of low-cost, the material provides the same design strength compared to conventional material, and enables parts production with existing equipment. A review of manufacturing and surface treatment processes indicated a reduction in the price of titanium parts produced with this new material.

The variable intake and exhaust control valve system for the in-line four-cylinder motorcycle engine was developed for realization of high engine power in all the engine speed ranges. Both the variable intake and exhaust control valves are operated by one servomotor. For high engine speeds, the exhaust collector pipe design for merging of each exhaust gas flow at 180 degrees phase difference is used. For mid engine speeds, the design for merging of each exhaust gas flow at 360 degrees phase difference is used. Two modes are provided to the intake control, and three modes are provided to the exhaust control. Along with exhaust-gas treatment systems such as the catalyst and air-injection system, high engine performance with optimum driveability and reduced emission are realized.

High rigidity and light weight properties of the frames and swing-arms of motorcycles for motocross are requested. A twin-tube type frame using newly developed aluminum alloy having tensile strength of 450MPa and a tapered swing-arm made by a new manufacturing method have been developed. As a result, the weight of the frame and swing-arm was reduced by 2000g and the lateral rigidity and torsional rigidity of the frame were achieved at 2 times and 1.7 times compared with the previous models, and improve driving stability and acceleration.

Production of a relatively inexpensive titanium connecting rod for a mass production motorcycle engine has been achieved. Previously, the high cost of Titanium and other factors limited its usage by the aerospace industry and motor sports racing. As a material for mechanical parts titanium is light in weight and high in strength. In the engines of racing motorcycles the connecting rods, valves, and valve spring retainers which have been fabricated from a titanium alloy enhance the engine's performance.-1, -2 The cost of titanium alloy and its surface treatment is very expensive. -3, -4 Therefore the cost of the material was prohibitive and limited the application of titanium to competition machines. This paper outlines the development of a new surface treatment and application to titanium connecting rods. It was specifically applied to the connecting rods of a 750 cc motorcycle in 1987, the first in this field of industry. -5, -6, -7