TM 9-2320-272-24-4
5-10. PISTON AND CONNECTING ROD MAINTENANCE (Contd)
NOTE
First and second piston ring groove widths are checked for wear
the same way. Step 17 checks top ring groove width for wear.
17.
Place and hold new piston ring (2) in top ring groove (3) and try to insert 0.006 in. (0.15 mm) feeler
gauge into ring groove (3) at top of piston ring (2). If feeler gauge enters either ring groove (3)
without force, piston (1) is not serviceable and must be discarded.
18.
Repeat step 17 for second ring groove (4).
NOTE
Measurements to check piston skirt outside diameters are taken
at right angle to piston bore.
19.
Measure piston (1) upper skirt outside diameter (6) approximately 1 in. (25.4 mm) below bottom
ring groove (4) with micrometer.
20.
Measure piston (1) bottom skirt outside diameter (7) approximately 1 in. (25.4 mm) above skirt bottom (8).
If outside diameters (6) and (7) measure less than 5.483 in. (139.27 mm), discard piston (1).
21.
Measure piston pin bore (5) inside diameter. If inside diameter exceeds 1.99 in. (50.775 mm) at 70F
(21C), discard piston (1). Add .0005 in. (0.13 mm) per each 10F over 70F (21C) up to 90F (32C).
22.
Check outside diameter of piston pin (9) with micrometer. If outside diameter is worn out-of-round
more than 0.001 in. (0.03 mm), discard piston pin (9). If diameter is smaller than 1.99885 in.
(50.762 mm), discard piston pin (9).
23.
Check all piston (1) parts to be sure they are numbered the same. Number is generally located on
the inside of piston (1) skirt.
NOTE
New piston rings must be checked in the cylinder liner in which
they will be used to ensure ring gaps are correct.
24.
Insert piston rings (11), (13), (14), and (15) in each mating cylinder liner (10) bore, using head (top)
of piston (1) to position piston ring (11) so it seats squarely in piston ring (11) travel area.
25.
Measure ring gap (12) with feeler gauge. Ring gap (12) should meet specifications given in
NOTE
Add 0.003 in. (0.08 mm) ring gap to new maximum for each 0.001
in. (0.03 mm) wear in cylinder liner wall. Measurement made in
ring travel area of liner.
Table 5-8. Ring Gap.
0.023-0.033 in.
No. 1 compression ring (13) gap
(0.58-0.85 mm)
0.019-0.029 in.
No. 2 and 3 compression ring (11) and (14) gap
(0.48-0.74 mm)
0.010-0.025 in.
No. 4 oil ring (15) gap
(0.25-0.64 mm)
26.
Install piston rings (13), (11), (14), and (15) in piston (1) with piston ring expander. Ensure the word
"top" faces toward top of piston (1).
27.
Check connecting rod journals (17) on crankshaft assembly (16) for scores and scratches. If scored or
scratched, replace crankshaft.
28.
Check connecting rod journals (17) for out-of round wear with micrometer. If worn more than 0.002
in. (0.05 mm), replace crankshaft.
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