When two moving metallic parts lose lubrication between them, scuffing is likely to occur. Scuffing is the process by which the metals weld themselves together and then break loose. Welding can occur between the piston or piston rings and the cylinder walls when the piston stops at TDC. As the piston starts back down from TDC, this weld breaks. The rough surface that results wears ridges in the cylinder wall and on the piston ring or the piston itself. Scuffing can also be caused by detonation, which causes higher temperatures and pressures in the combustion chambers.

 

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