Lexus SC300 / Lexus SC400. Manual — part 435

3.

REMOVE ENGINE HANGERS

4.

REMOVE ENGINE COOLANT TEMPERATURE SENSOR
AND SENDER GAUGE

5.

REMOVE THROTTLE CABLE BRACKET AND GROUND
STRAP

6.

REMOVE EGR COOLER

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 surface.

(b)

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

(c)

Using compressed air, blow carbon and oil from the bolt
holes.

CAUTION: Protect your eyes when using high–com-
pressed air.

2.

CLEAN CYLINDER HEAD

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.

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ENGINE MECHANICAL

Cylinder Head

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.

D.

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

3.

INSPECT CYLINDER HEAD

A.

Inspect for flatness
Using precision straight edge and feeler gauge, measure the
surfaces contacting the cylinder block, intake and exhaust
manifolds for warpage.

Maximum warpage: 0.10 mm (0.0039 in.)

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

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ENGINE MECHANICAL

Cylinder Head

EM–43

B.

Inspect for cranks
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.

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 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

(0.0012–0.0036 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.

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ENGINE MECHANICAL

Cylinder Head

6.

IF NECESSARY, REPLACE VALVE GUIDE BUSHINGS
(a) Using SST and a hammer, tap out the guide bushing.
SST 09201–70010

(b)

Using a caliper gauge, measure the bushing bore
diameter of the cylinder head.

(c)

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

Both intake and exhaust

If the bushing bore diameter of the cylinder head is greater
than 11.044 mm (0.4348 in.), machine the bushing bore to
the following dimension:

11.035–11.056 mm (0.4344–0.4353 in.)

If the bushing bore diameter of the cylinder head is greater
than 11.056 mm (0.4353 in.), replace the cylinder head.

(d)

Using SST and hammer, tap in a new guide bushing to
the specified protrusion height.

SST 09201–70010

Protrusion height:

Intake

12.3–12.7 mm (0.484–0.500 in.)

Exhaust

11.4–11.8 mm (0.449–0.465 in.)

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

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ENGINE MECHANICAL

Cylinder Head

EM–45