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The fracture splitting (FS) method for case hardened connecting rods has been developed to improve engine performance while decreasing production costs. The FS method is widely used for automotive connecting rods because it effectively improves their productivity. Normalized forging steels, microalloyed forging steels and powder metals have generally been used as the material in the FS method as they are easily split due to their brittleness. On the other hand, the materials to be used for high performance motorcycles are case hardened low carbon steels because they allow the connecting rods to be lightweight due to their high fatigue strengths. These materials, which have a hardened area of approx. 0.5mm in depth from the surface, have a ductile texture inside. This texture obstructs the crack propagation and makes the split force too high to split without deforming the bearing area.

Hard anodic oxide coating (hard anodizing) technology giving hardness values above HV300 was developed for a piston alloy containing a high Cu concentration (Al-12%Si-4Cu-0.5Mg). This technology was developed to improve the result that the anodic oxide coating in a sulfuric acid bath on the alloy can give hardness values as low as HV200. The combination of mixed acid electrolytes (40gL-1 oxalic acid and sulfuric acid less than 150gL-1) and periodic reverse electrolyzing enables the piston-ring groove to form a hard anodic oxide coating film having hardness values above HV300, coating thickness of 20 μm, and surface roughness of Ra 2.0μm. This mixed acid electrolyzing was found to prevent the electrochemical dissolution of Cu. The periodic reverse waveform cools the piston-ring groove to prevent burning.

The present work was intended to increase the rolling-contact fatigue life of the crank pin for a motorcycle. The small motorcycle uses a needle roller bearing at the big end of the connecting rod. The needle roller exerts high Hertzian stress on the crank pin. This stress sometimes causes rolling-contact fatigue failure such as pitting. The contaminated oil accelerates the rolling-contact fatigue failure. In order to increase the life of the crank pin, not only the quality of the steel but also the casehardening treatment plays an important role. In the present work, a high quality Cr-Mo steel containing oxygen concentration below 10 ppm was chosen as the base steel. The rolling-contact fatigue life was compared in four types of casehardening: normal carburizing, carbonitriding, super-carburizing and super-carbonitriding. A thrust-type testing machine was used during these comparison tests.

A high-quality die-casting technology has been developed for lightweight aluminum frame structures that produces high-strength aluminum parts that are also weldable. This new technology has been used in casting frames for motorcycles and snowmobiles and has enabled improved frame designs with far fewer component parts than was possible before. This die-casting technology also results in a significant reduction in energy consumption during the manufacturing process.