Fitting Piston Rings

Piston rings are of two types - compression (plain face) and oil control ring. The two compression rings a re positioned in the two upper piston ring grooves with the stamped word 'TOP" or a dot (.) upward. Rings are regularly supplied in the following oversizes to fit standard oversize pistons: .010, .020, .030, .040, .050, .060 and .070 in.

Compression rings must have proper side clearance in ring grooves. Check with thickness gauge as shown in Figure 3-13. Ring gap (space between ends) must also be as specified, see "Specifications," Section 3.

The oil ring is a full width slotted oil control 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 of cylinder. Place ring in cylinder bore squarely against piston and check gap with thickness gauge (see Figure 3-14).

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

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

Use a commercially available piston ring expander (Figure 3-15) to guide and slip rings over the piston into their respective grooves without over expanding or twisting rings and damaging the finely finished piston surface.

Figure 3-15. Assembling Rings with Ring Expander
Figure 3-14. Checking Ring Gap

Figure 3-13. Measuring Ring Side Clearance

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