Hitachi CG 25EUAP (L) Service Manual page 17

8. Piston and piston ring
(1) Disassembly
Use long-nose pliers to remove the Circlip [52]. Pull out the Piston Pin [53], and then remove the
Piston [51].
Remove the 1st Ring [48] and 2nd Ring [49] while opening their slits.
The Oil Ring [50] consists of one expander and two scrapers. To remove the Oil Ring [50], first remove
the two scrapers by opening their slits, and then remove the expander.
(2) Reassembly
Check the Piston [51] for damage. Remove any carbon accumulated on the head of the Piston [51].
Use long-nose pliers to set the front end of the Circlip [52] in the groove on the Piston [51], and then
turn the other part of the Circlip [52] around the Piston [51] to fit the entire Circlip [52] into the groove.
Mount the piston rings in order of the Oil Ring [50], 2nd Ring [49], and 1st Ring [48]. To mount the Oil
Ring [50], mount the expander first, and then mount the scrapers. When mounting the 2nd Ring [49],
position it so that the "R" mark at its slit faces upward. After mounting, check that each piston ring turns
smoothly, and then turn the 1st Ring [48] to shift the position of its slit by about 180 degrees from that
of the 2nd Ring [49].
CAUTION: • When mounting the Piston Pin [53], be sure to prevent the Piston Pin [53] from
touching the Circlip [52].
• Do not confuse the 1st Ring [48] and 2nd Ring [49].
• Piston
Slit in the 2nd Ring [49]
Scraper
Expander
Scraper
Slit positions
"R" mark
Slit in the 1st Ring [48]
[51]
Slit in the 2nd Ring [49]
-16-
[48]
[49]
[50]
[53]
[51]
[52]
[52]