Subaru Impreza 3 / Impreza WRX / Impreza WRX STI. 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