Lexus SC300 / Lexus SC400. Manual - part 436

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

obtain the standard specified clearance (See page
EM–45) 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: 0.8–1.2 mm

(0.031–0.047 in.)

Minimum margin thickness: 0.5 mm (0.020 in.)

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

(d)  Check the valve overall length.

Standard overall length:

Intake 

98.29–98.79 mm (3.8697–3.8894 in.)

Exhaust 

98.84–99.34 mm (3.8657–3.9110 in.)

Minimum overall length:

Intake 

98.19 mm (3.8657 in.)

Exhaust 

98.74 mm (3.8874 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.

EM–46

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ENGINE MECHANICAL

Cylinder Head

8. 

INSPECT AND CLEAN VALVE SEATS
(a)  Using a 45

 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 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:

Intake

1.0–1.4 mm (0.039–0.055 in.)

Exhaust

1.2–1.6 mm (0.047–0.063 in.)

If not, correct the valve seats as follows:

(1)

 If the seating is too high on the valve face, use 15

°

and 45

°

 cutters to correct the seat.

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

°

and 45

°

 cutters to correct the seat.

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ENGINE MECHANICAL

Cylinder Head

EM–47

(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 deviation is greater than maximum, replace the valve
spring.

(b)

Using vernier calipers, measure the free length of the
valve spring.

Free length:

Pink painted mark 

41.74 mm (1.6433 in.)

White painted mark  41.50 mm (1.6339 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:

186–206 N (19–21 kgf, 42–46 lbf) at 34.5 mm (1.358 in.)

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

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.

EM–48

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ENGINE MECHANICAL

Cylinder Head

B.

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

Standard cam lobe height:

Intake 

44.570–44.670 mm (1.7547–1.7587 in.)

Exhaust 

44.250–44.350 mm (1.7421–1.7461 in.)

Maximum cam lobe height:

Intake 

44.42 mm (1.7488 in.)

Exhaust 

44.10 mm (1.7362 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: 

28.949–28.965 mm

(1.1397–1.1404 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.

E.

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 2 on page EM–55)

Torque:

20 N

⋅

m (200 kgf

⋅

cm, 14 ft

⋅

lbf)

HINT: Do not turn the camshaft.

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ENGINE MECHANICAL

Cylinder Head

EM–49