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In recent years, the demand for fuel economy of small engines has been increasing for further improvement of product competitiveness. As a solution for this issue, a lot of developments on reduction of friction losses of engine components have been actively performed by engine manufacturers, especially the friction loss between the cylinder bores and pistons or piston rings is main issue to solve because these frictions highly contribute to the fuel economy for the small engines. In this study, focusing on the effect of the texture of the all-aluminum cylinder bore on friction loss, we verified the friction loss of all-aluminum cylinders having several kinds of surface textures by a floating liner method.

The two-stroke engines were in the main stream of the outboard motors, but they have been replaced with the four-stroke counterparts reflecting the environmental protection movement in recent years. However, the replacement with four-stroke engines involves increased number of components and additional displacement, and the outboard motors tend to be larger and heavier. This represents an issue, since the maneuverability of the boat is degraded due to the inappropriate weight distribution on the boat. Yamaha outboard motors F300B and VF250A, of which the production started in the year 2009, are equipped with four-stroke engines, and yet achieved the light weight equivalent to their two-stroke counterparts. The production volume of these models reached 20,000 units.