Fitting Piston Rings

If cylinders are worn less than the .002 in. maximum and refinishing is not necessary, (unless they are scuffed or grooved) the same pistons may be used with the replacement of rings. However, before reassembling it is a good practice to rough up the cylinder wall with No. 150 Carborundum emery paper or a No. 300 hone. This will remove any high spots, carbon or foreign material from the cylinder wall and at the same time provide a surface suitable for proper lubrication and ring seating.

Piston rings are of two types - Compression (plain face) and oil control. The two compression rings are positioned in the two upper piston ring grooves, chamfered side up. Rings are available in following oversizes to fit standard oversize pistons: .010, .020, .030, .040, .050, .060 and .070 in.

The rings must have proper side clearance in ring grooves. See "Specifications" Section 3A. Check with thickness gauge as shown in Fig. 3C-20. Gap between ends of rings when inserted squarely in cylinder bore must also be as specified in Section 3 A.

The oil control ring is a full width slotted ring using a spring expander.

To check ring gap place a piston in cylinder with top end of piston about 1/2 in. from top end of cylinder. Set the ring to be checked in cylinder bore squarely against piston. With a thickness gauge, check ring gap as shown in Fig. 3C-21.

Use only standard size rings and piston in standard bore, and only matching oversize rings and pistons in same oversize bore.

If cylinder has been refinished oversize, use the correct oversize rings, fitting rings to give standard gap.

If gap is less than specified, ring ends may butt under expansion, and rings may be scored or broken. Gap may be increased by filing with a fine-cut file.

The two chrome plated compression rings, recognized by bright finish, are used in top and second ring grooves, with chamfer on one edge of the inside

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Figure 3C-20. Measuring Ring Clearance in Grooves

Figure 3C-21. Measuring Piston Compression Figure 3C-19. Measuring Piston Ring Gap


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