Figure 3-20.—Ring groove shoulders due to wear.usually requires replacement of the piston since theshoulders prevent the proper fitting of new rings.After determining that a piston is serviceable,inspect the rings carefully todetermine whether they canbe reused. If they do not meet specifications, you mustinstall new rings.When installing rings, measure the gap with a feelergauge. To measure the gap, place the new rings insidethe cylinder liner (fig. 3-21, view A) or in a ring gauge.When the gap is measured with the ring in the liner (fig.3-21, view B), two measurements are necessary—onejust below the upper limit of ring travel, and the otherwithin the lower limit of travel. These measurements arenecessary because the liner may have a slight amount oftaper caused by wear. The ring gap must be within thelimits specified in the manufacturer’s technical manual.If the gap of a new ring is less than specified, file theends of the ring with a straight-cut mill file to obtain theproper gap. If the gap is more than specified, installoversized rings.To measure the ring gap of used rings, hold the ringsin place on the piston with a ring compressing tool (fig.3-22). But before you measure the ring gap with the ringon the piston, first measure the piston for wear andout-of-roundness.After ensuring the proper gap clearance, you canreinstall the piston pin and connecting rod. Duringreassembly and installation of a piston and connectingrod assembly, be sure that all parts are well lubricated.Install the rings on the piston with tools similar to thoseused for ring removal. When installing piston rings,spread them as little as possible to avoid breaking therings. Insert the lowest ring first. When all the rings haveFigure 3-21.–A. Leveling a piston ring. B. Measuring ring gap clearance in a cylinder bore.3-15
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