A Study of Torn and Folded Metal (TFM) on Honed Cylinder Bore Surfaces

Torn and folded metal (TFM) on honed cylinder bore surfaces has been observed and studied for decades. However, there is no objective and quantitative method for ranking the severity of TFM. Studies on its effect on the scuffing resistance of a cylinder bore and piston skirt/piston ring are also very limited. Machined surfaces are currently evaluated and ranked qualitatively based on fax film images. The results may vary greatly depending upon the individual's experience and also the image quality. In this study, an attempt has been made to develop a method that can be used to evaluate cylinder bore surfaces objectively. A “surface index” has been developed for classifying honed bore surfaces. To further examine the effect of TFM on a cylinder bore performance, bench tests have been conducted to evaluate cylinder bore scuffing resistance and its correlation with the bore surface quality in terms of the value of the surface index.