We measured the friction of piston pin boss bearings for a gasoline engine to make sure of the state of lubrication. In addition, we checked how the shape of the piston pin as well as that of the pin boss influenced the state of bearing lubrication, which was analyzed according to the FEM calculations of pin and bearing contact pressure. As a result, it was made clear that the state of bearing lubrication sharply deteriorated at an engine speed of 3500 rpm or higher because the deformed pin caused the pin edge to heavily come into contact with the bearing, and a side relief was able to improve the state of lubrication at a high engine speed. We also gave a check to the piston pin for thickness to see how it influenced the state of lubrication, finding that a lighter-weight pin led to the deterioration of lubrication.

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