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Recent automotive engines for high performance vehicles have been designed for higher speeds and outputs. Not only the combustion load but also the inertia force applied on the connecting rod has been increasing. Automotive engines have also become compact and lighter in weight for needs of lower fuel consumption. For these reasons, the rigidity of the connecting rod has been reduced in comparison with the increasing inertia force. As a result, fretting damage may occur between two surfaces of the connecting rod big end bore and the bearing outer surface, causing breakage of the connecting rod itself. Countermeasures for fretting such as a tighter bearing fit ( interference ) and higher rigidity of the connecting rod big end are generally adopted. But the details for these countermeasures can not be easily predicted at the design stage. Rather they are obtained only by durability tests on the actual engines.