Figure 12-15.—Piston assembly.Figure 12-16.—Cam-ground piston.The piston is kept in alignment by the skirt, which isusually cam ground (elliptical in cross section) (fig.12-16).This elliptical shape permits the piston to fit the cylinder,regardless of whether the piston is cold or at operatingtemperature. The narrowest diameterof the piston is at the piston pin bosses, where the pistonskirt is thickest. At the widest diameter of the piston, thepiston skirt is thinnest. The piston is fitted to close limitsat its widest diameter so that the piston noise (slap) isprevented during the engine warm-up. As the piston is12-15
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