Lexus LS400 (2000 year). Manual — part 89

EM09S–02

A03194

A03193

EM6323

EM6324

P21861

EM–44

–

ENGINE MECHANICAL

CYLINDER HEAD

1226

INSPECTION

1.

CLEAN TOP SURFACES OF PISTONS AND CYL-
INDER BLOCK

(a)

Turn the crankshaft, and bring each piston to top dead
center (TDC). Using a gasket scraper, remove all the car-
bon 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 pressure compressed
air.

2.

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 sur-
face.

3.

CLEAN COMBUSTION CHAMBERS

Using a wire brush, remove all the carbon from the combustion
chambers.
NOTICE:
Be careful not to scratch the cylinder block contact sur-
face.

4.

CLEAN VALVE GUIDE BUSHINGS

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

EM6325

A02876
A02877
A02878

A02879

EM6327

EM0580

–

ENGINE MECHANICAL

CYLINDER HEAD

EM–45

1227

5.

CLEAN CYLINDER HEAD

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

6.

INSPECT FOR FLATNESS

Using a precision straight edge and feeler gauge, measure the
surfaces 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.

7.

INSPECT FOR CRACKS

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

8.

CLEAN VALVES

(a)

Using a gasket scraper, chip off any carbon from the valve
head.

(b)

Using a wire brush, thoroughly clean the valve.

P21862

Z00052

Z00054

44.5

°

EM0181

Margin Thickness

EM–46

–

ENGINE MECHANICAL

CYLINDER HEAD

1228

9.

INSPECT VALVE STEMS AND GUIDE BUSHINGS

(a)

Using a caliper gauge, measure the inside diameter of the
guide bushing.
Bushing inside diameter:
5.510 – 5.530 mm (0.2169 – 0.2177 in.)

(b)

Using a micrometer, measure the diameter of the valve
stem.
Valve stem diameter:

Intake

5.470 – 5.485 mm (0.2154 – 0.2159 in.)

Exhaust

5.465 – 5.480 mm (0.2152 – 0.2157 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. (See Page

EM–54

)

10.

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.
Margin thickness:

Standard

1.0 mm (0.039 in.)

Minimum

0.5 mm (0.020 in.)

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

EM2534

Overall Length

EM0255

EM6330

45

°

Carbide Cutter

Z00055

Width

Z03988

45

°

30

°

1.0 – 1.4 mm

–

ENGINE MECHANICAL

CYLINDER HEAD

EM–47

1229

(d)

Check the valve overall length.
Standard overall length:

Intake

95.05 mm (3.7421 in.)

Exhaust

95.10 mm (3.7441 in.)

Minimum overall length:

Intake

94.55 mm (3.7224 in.)

Exhaust

94.60 mm (3.7244 in.)

If the overall length is less than minimum, replace the valve.

(e)

Check the surface of the valve stem tip for wear.

If the valve stem tip is worn, resurface the tip with a grinder or
replace the valve.
NOTICE:
Do not grind off more than minimum.

11.

INSPECT AND CLEAN VALVE SEATS

(a)

Using a 45

°

carbide cutter, resurface the valve seats. Re-

move only enough metal to clean the seats.

(b)

Check the valve seating position.
Apply a light coat of prussian blue (or white lead) to the
valve face. Lightly press the valve against the seat. Do not
rotate valve.

(c)

Check the valve face and seat for the following:

If blue appears 360

°

around the face, the valve is

concentric. If not, replace the valve.

If blue appears 360

°

around the valve seat, the

guide and face are concentric. If not, resurface the
seat.

Check that the seat contact is in the middle of the
valve face with the following width:

1.0 – 1.4 mm (0.039 – 0.055 in.)

If not, correct the valve seats as follows:

If the seating is too high on the valve face, use 30

°

and 45

°

cutters to correct the seat.