12. Erosion—loss of metal from the surface by mechanical  action of foreign objects, such as grit or fine sand. The  eroded area is rough and may be lined in the direction  that the foreign material moved relative to the surface. 13. Flaking—the breaking loose of small pieces of metal  or coated surfaces, that is usually caused by defective  plating or excessive loading. 14. Fretting—a condition of surface erosion caused by  minute movement between two parts usually clamped  together with considerable unit pressure. 15. Galling—a severe condition of chafing or fretting in  which a transfer of metal from one part to another  occurs. It is usually caused by a slight movement of  mated parts having limited relative motion and under  high loads. 16. Gouging—a furrowing condition in which a  displacement of metal has occurred (a torn effect).  It is usually caused by a piece of metal, or foreign  material, between close moving parts. 17. Grooving—a recess, or channel, with rounded and  smooth edges usually caused by faulty alignment  of parts. 18. Inclusion—presence of foreign or extraneous material  entirely within a portion of metal. Such material is  introduced during the manufacture of rod, bar, or  tubing by rolling or forging. 19. Nick—a sharp-sided gouge or depression with a  V-shaped bottom, that is generally the result of  careless handling of tools and parts. 20. Peening—a series of blunt depressions in a surface. 21. Pick up or scuffing—a buildup or rolling of metal  from one area to another, that is usually caused by  insufficient lubrication, clearances, or foreign matter. 22. Pitting—small hollows of irregular shape in the  surface, usually caused by corrosion or minute  mechanical chipping of surfaces. 23. Scoring—a series of deep scratches caused by foreign  particles between moving parts or careless assembly  or disassembly techniques. 24. Scratches—shallow, thin lines or marks, varying in  degree of depth and width, caused by presence of fine  foreign particles during operation or contact with other  parts during handling. 25. Stain—a change in color, locally, causing a noticeably  different appearance from the surrounding area. 26. Upsetting—a displacement of material beyond the  normal contour or surface (a local bulge or bump).  Usually indicates no metal loss. 1.  Interior surfaces of piston pins 2.  The fillets at the edges of crankshaft main and crankpin  journal surfaces 3.  Thrust bearing races Cylinder Head Examine all gears for evidence of pitting or excessive wear.  These conditions are of particular importance when they  occur on the teeth; deep pit marks in this area are sufficient  cause to reject the gear. Bearing surfaces of all gears should  be free from deep scratches. However, minor abrasions  usually can be dressed out with a fine abrasive cloth. All bearing surfaces should be examined for scores, galling,  and wear. Considerable scratching and light scoring of  aluminum bearing surfaces in the engine do no harm and  should not be considered a reason for rejecting the part,  provided it falls within the clearances set forth in the table of  limits in the engine manufacturer’s overhaul manual. Even  though the part comes within the specific clearance limits, it is  not satisfactory for re-assembly in the engine unless inspection  shows the part to be free from other serious defects. Ball bearings should be inspected visually and by feel for  roughness, flat spots on balls, flaking or pitting of races,  or scoring on the outside of races. All journals should  be checked for galling, scores, misalignment, or out-of- round condition. Shafts, pins, etc., should be checked for  straightness. This may be done, in most cases, by using  V-blocks and a dial indicator. Pitted surfaces in highly stressed areas, resulting from  corrosion, can cause ultimate failure of the part. The  following areas should be examined carefully for evidence  of such corrosion: If pitting exists on any of the surfaces mentioned, to the extent  that it cannot be removed by polishing with crocus cloth or  other mild abrasive, the part usually must be rejected. Parts, such as threaded fasteners or plugs, should be inspected  to determine the condition of the threads. Badly worn or  mutilated threads cannot be tolerated; the parts should be  rejected. However, small defects, such as slight nicks or burrs,  may be dressed out with a small file, fine abrasive cloth,  or stone. If the part appears to be distorted, badly galled,  mutilated by overtightening, or from the use of improper  tools, replace it with a new one. Inspect the cylinder head for internal and external cracks.  Use a bright light to inspect for cracks and investigate any  suspicious areas with a magnifying glass or microscope.  Carbon deposits must be cleaned from the inside of the  10-4