Lexus SC300 / Lexus SC400. Manual - part 445

INSPECTION, CLEANING AND REPAIR
OF CYLINDER HEAD COMPONENTS

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 surfaces.

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

from the top surfaces of the cylinder block.

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

holes.

CAUTION: Protect your eyes when using high–pressure
compressed air.

2. 

CLEAN CYLINDER HEADS

A.

Remove gasket material Using a gasket scraper, remove
all the gasket material from the cylinder block surface.
NOTICE: Be careful not to scratch the cylinder block con-
tact surface.

B.

Clean combustion chambers
Using a wire brush, remove all the carbon from the combus-
tion chambers.
NOTICE: Be careful not to scratch the cylinder block con-
tact surface.

C.

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

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ENGINE MECHANICAL

Cylinder Heads

D. Clean cylinder heads

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

3. 

INSPECT CYLINDER HEADS

A.

Inspect for flatness
Using a precision straight edge and feeler gauge, measure
the surfaces contacting the cylinder block and 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 any carbon from the valve

head.

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

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ENGINE MECHANICAL

Cylinder Heads

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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 diameter measurement of the valve stem

from the inside diameter measurement of the guide
bushing.

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

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ENGINE MECHANICAL

Cylinder Heads

(b)  Gradually heat the cylinder head to 80–1005C (176

–2125F).

(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.

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
(0.4331–0.4342)

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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

(e)  Select a new guide bushing (STD size or O/S 0.05).
If the bushing bore diameter of the cylinder head is greater
than 11.027 mm (0.4341 in.), grind 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.

(f)  Gradually heat the cylinder head to 80–1005C (176

–2125F).

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ENGINE MECHANICAL

Cylinder Heads

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