Lexus SC300 / Lexus SC400. Service manual — part 570

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

EM–79

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.

EM–80

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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

EM–81

(g) Using SST and a hammer, tap in a new guide bushing

until the snap ring makes contact with the cylinder head.

SST 09201–70010

HINT: Different the bushings are used for the intake and ex-
haust.

(h) Using a sharp 6 mm reamer, ream the guide bushing to

obtain the standard specified clearance (See page

EM–80

) between the guide bushing and valve stem.

7.

INSPECT AND GRIND VALVES
(a) Grind the valve enough to remove pits and carbon.
(b) Check that the valve is ground to the correct valve face

angle.

Valve face angle: 44.5

°

(c) Check the valve head margin thickness.

Standard margin thickness: 1.0 mm (0.039 in.)

Minimum margin thickness: 0.5 mm (0.020 in.)

If the margin thickness is less than minimum, replace the
valve.

EM–82

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ENGINE MECHANICAL

Cylinder Heads