Subaru 2009 IMPREZA Service Manual page 307

4) Check the snap ring installation groove (A) on
the piston for burr. If necessary, remove burr from
the groove so that the piston pin can lightly move.
(A)
5) Check the piston pin snap ring for distortion,
cracks and wear.
4. PISTON RING
1) If the piston ring is broken, damaged or worn, or
if its tension is insufficient, or when the piston is re-
placed, replace the piston ring with a new part of
the same size as piston.
NOTE:
• The top ring and second ring have the mark to
determine the direction for installing. When install-
ing the ring to piston, face marks to the top side.
• Oil ring consists of the upper rail, expander and
lower rail. When installing oil ring on piston, be
careful of the direction of each rail.
(A) Upper rail
(B) Expander
(C) Lower rail
Cylinder Block
2) Using the piston, insert the piston ring and oil
ring into the cylinder so that they are perpendicular
to the cylinder wall, and measure the piston ring
gap with a thickness gauge.
Piston ring gap
ME-00175
3) Fit the piston ring straight into the piston ring
groove, then measure the clearance between pis-
ton ring and piston ring groove with a thickness
gauge.
NOTE:
Before measuring the clearance, clean the piston
ring groove and piston ring.
(A)
Clearance
(B)
between piston
ring and piston
(C)
ring groove
(A)
(B)
(C)
ME-02480
ME(H4SO)-89
MECHANICAL
Standard
0.20 — 0.35
Top ring
(0.0079 — 0.0138)
0.37 — 0.52
Second ring
(0.0146 — 0.0205)
0.20 — 0.50
Oil ring rail
(0.0079 — 0.0197)
Standard
0.040 — 0.080
Top ring
(0.0016 — 0.0031)
0.030 — 0.070
Second ring
(0.0012 — 0.0028)
mm (in)
ME-00177
mm (in)
ME-00178