Subaru 2009 IMPREZA Service Manual page 306

MECHANICAL
3) When the piston is to be replaced due to general
or cylinder wear, select a suitable sized piston by
measuring the piston clearance.
4) Measure outer diameter of each piston.
Measure the outer diameter of each piston at the
height as shown in the figure. (Thrust direction)
NOTE:
Measurement should be performed at a tempera-
ture of 20°C (68°F).
Piston grade point H:
38.2 mm (1.504 in)
Piston outer diameter:
Standard
A: 99.505 — 99.515 mm (3.9175 — 3.9179 in)
B: 99.495 — 99.505 mm (3.9171 — 3.9175 in)
0.25 mm (0.0098 in) oversize:
99.745 — 99.765 mm (3.9270 — 3.9277 in)
0.50 mm (0.0197 in) oversize:
99.995 — 100.015 mm (3.9368 — 3.9376 in)
5) Calculate the clearance between cylinder and
piston.
NOTE:
Measurement should be performed at a tempera-
ture of 20°C (68°F).
Cylinder to piston clearance at 20°C (68°F):
Standard:
–0.010 — 0.010 mm (–0.00039 — 0.00039 in)
6) Boring and honing
(1) If any of the measured value of taper, out-of-
roundness or cylinder-to-piston clearance is out
of standard or if there is any damage on the cyl-
inder wall, rebore it to replace with an oversize
piston.
CAUTION:
When any of the cylinders needs reboring, all
other cylinders must be bored at the same time,
and replaced with oversize pistons.
Cylinder Block
(2) If the cylinder inner diameter exceeds the
limit after boring and honing, replace the cylin-
der block.
NOTE:
Immediately after reboring, the cylinder diameter
may differ from its real diameter due to temperature
rise. Thus, when measuring the cylinder diameter,
wait until it has cooled to room temperature.
Cylinder inner diameter boring limit:
To 100.005 mm (3.9372 in)
3. PISTON AND PISTON PIN
1) Check the piston and piston pin for breaks,
cracks or wear. Replace if faulty.
2) Check the piston ring groove for wear and dam-
age. Replace if faulty.
3) Make sure that the piston pin can be inserted
into the piston pin hole with a thumb at 20°C (68°F).
Replace if faulty.
Clearance between piston hole and piston pin:
Standard:
0.004 — 0.008 mm (0.0002 — 0.0003 in)
H
ME-00172
ME(H4SO)-88
ME-00173
ME-00174