Subaru Impreza 3 / Impreza WRX / Impreza WRX STI. Service manual — part 78
ME(STI)-74
Cylinder Head
MECHANICAL
D: ASSEMBLY
(1)
Exhaust valve
(5)
Intake valve oil seal
(9)
Valve lifter
(2)
Intake valve
(6)
Valve spring
(10) Exhaust valve oil seal
(3)
Cylinder head
(7)
Valve spring retainer
(11) Intake valve guide
(4)
Valve spring seat
(8)
Valve spring retainer key
(12) Exhaust valve guide
(3)
(1)
(12)
(10)
(4)
(6)
(7)
(8)
(9)
(10)
(4)
(6)
(7)
(8)
(9)
ME-04990
(12)
(2)
(11)
(4) (5)
(6)
(7) (8)
(9)
(11)
(4) (5)
(6)
(7) (8) (9)
ME(STI)-75
Cylinder Head
MECHANICAL
1) Install the valve spring and valve.
(1) Coat the valve stem of each valve with en-
gine oil and insert the valve into valve guide.
NOTE:
When inserting the valve into valve guide, use spe-
cial care not to damage the oil seal lip.
(2) Set the cylinder head on ST1.
ST1 498267600
CYLINDER HEAD TABLE
(3) Install the valve spring and valve spring re-
tainer.
NOTE:
Be sure to install the valve spring with its close-
coiled end facing the cylinder head side.
(4) Set the ST2 on valve spring.
ST2 499718000
VALVE SPRING REMOVER
(5) Compress the valve spring and fit the valve
spring retainer key.
(6) After installing, tap the valve spring retainers
lightly with a plastic hammer for better seating.
2) Apply oil to the surface of valve lifter.
3) Install the valve lifter.
E: INSPECTION
1. CYLINDER HEAD
1) Check for cracks or damage. Use liquid pene-
trant tester on the important sections to check for
fissures. Check that there are no marks of gas leak-
ing or water leaking on gasket installing surface.
2) Measure the warping of the cylinder head sur-
face that mates with cylinder block using a straight
edge (A) and thickness gauge (B).
If the warping exceeds the limit, correct the surface
by grinding it with a surface grinder.
Warping limit:
0.035 mm (0.0014 in)
Grinding limit:
0.3 mm (0.012 in)
Standard height of cylinder head:
127.5 mm (5.02 in)
NOTE:
Uneven torque for the cylinder head bolts can
cause warping. When reinstalling, pay special at-
tention to the torque so as to tighten evenly.
2. VALVE SEAT
Inspect the intake and exhaust valve seats, and
correct the contact surfaces with a valve seat cutter
if they are defective or when valve guides are re-
placed.
Contacting width W between valve and valve
seat:
Standard
Intake
0.6 — 1.4 mm (0.024 — 0.055 in)
Exhaust
1.2 — 1.8 mm (0.047 — 0.071 in)
ME-05003
ST1
ST2
ME-00126
(A)
(B)
ME-04721
W
ME-00287
ME(STI)-76
Cylinder Head
MECHANICAL
3. VALVE GUIDE
1) Check the clearance between valve guide and
valve stem. The clearance can be checked by mea-
suring respectively the outer diameter of valve
stem with a micrometer and the inner diameter of
valve guide with a caliper gauge.
Clearance between the valve guide and valve
stem:
Standard
Intake
0.030 — 0.057 mm (0.0012 — 0.0022 in)
Exhaust
0.040 — 0.067 mm (0.0016 — 0.0026 in)
2) If the clearance between valve guide and valve
stem exceeds the standard, replace the valve
guide or valve itself, whichever shows the greater
amount of wear or damage. See the following pro-
cedure for valve guide replacement.
Valve guide inner diameter:
6.000 — 6.012 mm (0.2362 — 0.2367 in)
Valve stem outer diameters:
Intake
5.955 — 5.970 mm (0.2344 — 0.2350 in)
Exhaust
5.945 — 5.960 mm (0.2341 — 0.2346 in)
(1) Place the cylinder head on ST1 with the
combustion chamber upward so that valve
guides fit the holes in ST1.
(2) Insert the ST2 into valve guide and press it
down to remove the valve guide.
ST1 498267600
CYLINDER HEAD TABLE
ST2 499767200
VALVE GUIDE REMOVER
(3) Turn the cylinder head upside down and
place the ST as shown in the figure.
ST 18251AA020 VALVE GUIDE ADJUSTER
(4) Before installing a new valve guide, make
sure that neither scratches nor damages exist
on the inner surface of valve guide holes in cyl-
inder head.
(5) Put a new valve guide, coated with sufficient
oil, in the cylinder head, and insert the ST1 into
valve guide. Press in until the valve guide upper
end is flush with the upper surface of ST2.
ST1 499767200
VALVE GUIDE REMOVER
ST2 18251AA020
VALVE GUIDE ADJUSTER
(6) Check the valve guide protrusion amount
“L”.
Valve guide protrusion amount L:
15.8 — 16.2 mm (0.622 — 0.638 in)
ME-05004
ST1
ST2
ST
ME-04107
ME-00130
ST1
ST2
L
ME-04522
ME(STI)-77
Cylinder Head
MECHANICAL
(7) Ream the inside of valve guide using ST.
Put the ST in valve guide, and rotate the ST
slowly clockwise while pushing it lightly. Bring
the ST back while rotating it clockwise.
NOTE:
• Apply engine oil to the ST when reaming.
• If the inner surface of valve guide is damaged,
the edge of ST should be slightly ground with oil
stone.
• If the inner surface of valve guide becomes lus-
trous and the ST does not chip, use a new ST or
remedy the ST.
ST 499767400
VALVE GUIDE REAMER
(8) After reaming, clean the valve guide to re-
move chips.
(9) Recheck the contact condition between
valve and valve seat after replacing the valve
guide.
4. INTAKE AND EXHAUST VALVE
1) Inspect the flange of valve and valve stem, and
replace the valve with a new part if damaged, worn,
deformed, or if dimension “H” in the figure is out-
side of the specified limit.
Head edge thickness H:
Standard
Intake (A)
1.0 — 1.4 mm (0.039 — 0.055 in)
Exhaust (B)
1.3 — 1.7 mm (0.051 — 0.067 in)
2) Put a small amount of grinding compound on the
valve seat surface, and lap the valve and valve seat
surface. Replace with a new valve oil seal after lap-
ping.
NOTE:
It is possible to differentiate between the intake
valve and the exhaust valve by their overall length.
Valve overall length:
Intake
104.4 mm (4.110 in)
Exhaust
104.65 mm (4.1201 in)
ME-04393
ST
ME-04825
(B)
(A)
H
H
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