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TM 10-4320-351-14
6.4.4 Install Piston Rings. (Refer to figure 6-26.)
This procedure applies to either piston.
This task consists of:
a. Installation
INITIAL SET-UP:
Tools:
Materials/Parts Required:
Caliper, Vernier
None
(Appendix B, Section III, Item 3)
Equipment Condition:
Piston and rings removed (para. 6.3.12)
a.
Inspect cylinder, piston and piston rings.
(1)
Insert the first compression ring (1) in the top of the cylinder. Measure and record the gap between the
ends of the ring. Remove the ring and repeat the procedure with the second compression ring (2) and the
oil scraper ring (3). If the ring gap is more than 0.02 inches or less than 0.01 inches, replace the cylinder.
(2)
Measure and record the piston skirt diameter (4) between 0.200 and 0.393 inches from the base of the
piston skirt.
(3)
Measure and record the inside diameter of the cylinder.
(4)
Subtract the piston skirt diameter (4) from the cylinder inside diameter. The difference should be 0.002 -
0.003 inches. If clearance is greater than 0.003 inches, replace cylinder/piston.
b.
Thoroughly clean piston (5) ensuring all carbon deposits are removed from piston top and ring grooves.
c.
Install rings on piston using the following steps:
NOTE
Install piston rings from top of piston.
(1)
Install oil scraper ring (3) in bottom piston groove. Rotate ring to place gap in line with one end of piston pin
(6).
(2)
Install second compression ring (2) in middle piston ring groove with internal bevel toward top of piston (5).
Rotate ring to place gap 120° in either direction from the gap in the oil scraper ring (3).
(3)
Install first compression ring (1) in top piston groove. Rotate ring to place gap midway on the longer arc
between oil scraper ring (3) gap and second compression ring (2) gap (120° from each of the other two
rings).
d.
Inspect rings to ensure all three piston rings move freely in grooves. Check the clearance between each piston
groove and each piston ring as follows. If any measurement exceeds the specified value, replace the piston.
6-42
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