Abstract: The invention provides a method of diagnosing a lubricated portion which can precisely measure a metal concentration in a lubricating oil and can diagnose accurately a state of the lubricated portion on the basis of a value of measurement. In accordance with the present diagnosing method, a lubricating oil picked up from the lubricated portion is diluted by an organic solvent so as to prepare a sample oil, the sample oil is filtrated by a filter so as to separate a large-diameter metal particle having a particle diameter larger than 0.5 ?m, a metal concentration of a solution formed by dissolving the large-diameter metal particle by an acid and a metal concentration of a filtrate including a small-diameter metal particle having a particle diameter equal to or smaller than 0.

Abstract: The invention provides a method of diagnosing a lubricated portion which can precisely measure a metal concentration in a lubricating oil and can diagnose accurately a state of the lubricated portion on the basis of a value of measurement. In accordance with the present diagnosing method, a lubricating oil picked up from the lubricated portion is diluted by an organic solvent so as to prepare a sample oil, the sample oil is filtrated by a filter so as to separate a large-diameter metal particle having a particle diameter larger than 0.5 ?m, a metal concentration of a solution formed by dissolving the large-diameter metal particle by an acid and a metal concentration of a filtrate including a small-diameter metal particle having a particle diameter equal to or smaller than 0.