Lexus SC300 / Lexus SC400. Service manual — part 368

EG1KM–02

CYLINDER HEAD COMPONENTS
INSPECTION AND REPAIR

1. CLEAN TOP SURFACES OF PISTONS AND CYLINDER

BLOCK

(a) Turn the crankshaft, and bring each piston to top dead center

(TDC). Using a gasket scraper, remove all the carbon from
the piston top surface.

(b) Using a gasket scraper, remove all the gasket material from

the cylinder block surface.

(c) Using compressed air, blow carbon and oil from the bolt

holes.

CAUTION: Protect your eyes when using high–compressed

air.

2.

CLEAN CYLINDER HEAD

A. Remove gasket material

Using a gasket scraper, remove all the gasket material from
the cylinder block contact surface.

NOTICE: Be careful not to scratch the cylinder block contact

surface.

B. Clean combustion chambers

Using a wire brush, remove all the carbon from the combus-
tion chambers.

NOTICE: Be careful not to scracth the cylinder block contact

surface.

C. Clean valve guide bushings

Using a valve guide bushing brush and solvent, clean all the
guide bushings.

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EG–95

D. Clean cylinder head

Using a soft brush and solvent, thoroughly clean the cylinder
head.

3. INSPECT

CYLINDER

HEAD

A. Inspect for flatness

Using a precision straight edge and feeler gauge, measure
the surface contacting the cylinder block and the manifolds
for warpage.

Maximum warpage:

0.10 mm (0.0039 in.)

If warpage is greater than maximum, replace the cylinder
head.

B. Inspect for cracks

Using a dye penetrant, check the combustion chamber, in-
take ports, exhaust ports and cylinder block surface for
cracks.
If cracked, replace the cylinder head.

4. CLEAN

VALVES

(a) Using a gasket scraper, chip off any carbon from the valve

head.

(b) Using a wire brush, thoroughly clean the valve.

EG–96

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5.

INSPECT VALVE STEMS AND GUIDE BUSHINGS

(a) Using a caliper gauge, measure the inside diameter of the

guide bushing.

Bushing inside diameter:

6.010 – 6.030 mm (0.2366 – 0.2374 in.)

(b) Using

a

micrometer, measure the diameter of the valve stem.

Valve stem diameter:

Intake

5.970 – 5.985 mm (0.2350 – 0.2356 in.)

Exhaust

5.965 – 5.980 mm (0.2348 – 0.2354 in.)

(c) Subtract the valve stem diameter measurement from the

guide bushing inside diameter measurement

Standard oil clearance:

Intake

0.025 – 0.060 mm (0.0010 – 0.0024 in.)

Exhaust

0.030 – 0.065 mm (0.0012 – 0.0026 in.)

Maximum oil clearance:

Intake

0.08 mm (0.0031 in.)

Exhaust

0.10 mm (0.0039 in.)

If the clearance is greater than maximum, replace the valve
and guide bushing.

6.

IF NECESSARY, REPLACE VALVE GUIDE BUSHINGS

(a) Insert an old valve wrapped with tape into the valve guide

bushing, and break off the valve guide bushing by hitting it
with a hammer. Remove the snap ring.
HINT: Wrap the tape approx. 8 mm (0.31 in.) from the valve
stem ends.

NOTICE: Be careful not to damage the valve lifter hole.

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(b) Gradually heat the cylinder head to 80 – 100

C (176 –

212

F).

(c) Using SST and a hammer, tap out the guide bushing.

SST 09201–70010

(d) Using a caliper gauge, measure the bushing bore diameter

of the cylinder head.

(e) Select a new guide bushing (STD or O/S 0.05).

Both intake and exhaust

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Bushing bore diameter

mm (in.)

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Bushing size

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11.000 – 11.027

(0.4331 – 0.4341)

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Use STD

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11.050 – 11.077

(0.4350 – 0.4361)

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Use O/S 0.05

V00228

If the bushing bore diameter of the cylinder head is greater
than 11.027 mm (0.4341 in.), machine the bushing bore to
the following dimension:
11.050 – 11.077 mm (0.4350 – 0.4361 in.)
If the bushing bore diameter of the cylinder head is greater
than 11.077 mm (0.4361 in.), replace the cylinder head.

HINT: Different bushings are used for the intake and exhaust.

EG–98

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