Figure 3-20.—Ring groove shoulders due to wear.

Figure 3-20.—Ring groove shoulders due to wear. usually requires replacement of the piston since the shoulders prevent the proper fitting of new rings. After determining that a piston is serviceable, inspect the rings carefully todetermine whether they can be reused. If they do not meet specifications, you must install new rings. When installing rings, measure the gap with a feeler gauge. To measure the gap, place the new rings inside the 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—one just below the upper limit of ring travel, and the other within the lower limit of travel. These measurements are necessary because the liner may have a slight amount of taper caused by wear. The ring gap must be within the limits specified in the manufacturer’s technical manual. If the gap of a new ring is less than specified, file the ends of the ring with a straight-cut mill file to obtain the proper gap. If the gap is more than specified, install oversized rings. To measure the ring gap of used rings, hold the rings in place on the piston with a ring compressing tool (fig. 3-22). But before you measure the ring gap with the ring on the piston, first measure the piston for wear and out-of-roundness. After ensuring the proper gap clearance, you can reinstall the piston pin and connecting rod. During reassembly and installation of a piston and connecting rod assembly, be sure that all parts are well lubricated. Install the rings on the piston with tools similar to those used for ring removal. When installing piston rings, spread them as little as possible to avoid breaking the rings. Insert the lowest ring first. When all the rings have Figure 3-21.–A. Leveling a piston ring. B. Measuring ring gap clearance in a cylinder bore. 3-15