Lexus SC300 / Lexus SC400. Manual — part 571

(d) Check the valve overall length.

Standard overall length:

Intake 94.95 mm (3.7382 in.)

Exhaust 96.90 mm (3.8150 in.)

Minimum overall length:

Intake 94.45 mm (3.7185 in.)

Exhaust 96.40 mm (3.7953 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 the minimum overall
length.

8.

INSPECT AND CLEAN VALVE SEATS
(a) Using a 455 carbide cutter, resurface the valve seats.
Remove only enough metal to clean the seats.

(b) Check the valve seating position.
Apply a thin coat of prussian blue (or white lead) to the valve
face. Lightly press the valve against the seat. Do not rotate
the valve.
(c) Check the valve face and seat for the following:

•

If blue appears 3605 around the face, the valve is
concentric. If not, replace the valve.

•

If blue appears 3605 around the valve seat, the
guide and face are concentric. If not, resurface the
seat.

•

Check that the seat contact is on 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:

(1)

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

°

and 45

°

cutters to correct the seat.

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ENGINE MECHANICAL

Cylinder Heads

EM–83

(2)

If the seating is too low on the valve face, use 75

°

and 45

°

cutters to correct the seat.

(d) Hand–lap the valve and valve seat with an abrasive

compound.

(e) After hand–lapping, clean the valve and valve seat.

9. INSPECT

VALVE

SPRINGS

(a) Using a steel square, measure the squareness of the

valve spring.

Maximum squareness: 2.0 mm (0.079 in.)

If squareness is greater than maximum, replace the valve
spring.

(b) Using a vernier caliper, measure the free length of the

valve spring.

Free length: 43.6 mm (1.717 in.)

If the free length is not as specified, replace the valve spring.

(c) Using a spring tester, measure the tension of the valve

spring at the specified installed length.

Installed tension (at 32.9 mm (1.295 in.):

186–206 N (19.0–21.0 kgf, 41.9–46.3 lbf)

If the installed tension is not as specified, replace the valve
spring.

EM–84

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ENGINE MECHANICAL

Cylinder Heads

10. INSPECT CAMSHAFTS AND BEARINGS
A.

Inspect camshaft for runout
(a) Place the camshaft on V–blocks.
(b) Using a dial indicator, measure the circle runout at the

center journal.

Maximum circle runout: 0.08 mm (0.0031 in.)

If the circle runout is greater than maximum, replace the cam-
shaft.

B.

Inspect cam lobes
Using a micrometer, measure the cam lobe height.

Standard cam lobe height:

Intake 41.710–41.810 mm

(1.6421–1.6461 in.)

Exhaust 41.910–42.010 mm

(1.6500–1.6539 in.)

Minimum cam lobe height:

Intake 41.56 mm (1.6362 in.)

Exhaust 41.76 mm (1.6441 in.)

If the cam lobe height is less than minimum, replace the cam-
shaft.

C.

Inspect camshaft journals
Using a micrometer, measure the journal diameter.

Journal diameter:

Exhaust camshaft thrust portion (A)

23.959–23.975 mm

(0.9433–0.9439 in.)

Others 26.954–26.970 mm

(1.0612–1.0618 in.)

If the journal diameter is not as specified, check the oil clear-
ance.

D.

Inspect camshaft bearings
Check the bearings for flaking and scoring.
If the bearings are damaged, replace the bearing caps and
cylinder head as a set.

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ENGINE MECHANICAL

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EM–85

E.

Inspect camshaft gear spring
Using a vernier caliper, measure the free distance between
the spring ends.

Free distance: 18.2–18.8 mm (0.712–0.740 in.)

If the free distance is not as specified, replace the gear
spring.

F. Inspect camshaft journal oil clearance

(a) Clean the bearing caps and camshaft journals.
(b) Place the camshafts on the cylinder head.
(c) Lay a strip of Plastigage across each of the camshaft

journals.

(d) Install the bearing caps.

(See step 7 on pages

EM–95

to 101)

Torque: 16 N

⋅

m (160 kgf

⋅

cm, 12 ft

⋅

lbf)

NOTICE: Do not turn the camshaft.

(e) Remove the bearing caps.

(f) Measure the Plastigage at its widest point.

Standard oil clearance:

Exhaust camshaft thrust portion

0.025–0.061 mm

(0.0010–0.0024 in.)

Others 0.030–0.067 mm

(0.0012–0.0026 in.)

Maximum oil clearance: 0.10 mm (0.0039 in.)

If the oil clearance is greater than maximum, replace the cam-
shaft. If necessary, replace the bearing caps and cylinder
head as a set.
(g) Completely remove the Plastigage.

EM–86

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ENGINE MECHANICAL

Cylinder Heads