Lexus SC300 / Lexus SC400. Manual — part 447

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

G.

Inspect camshaft thrust clearance
(a) Install the camshafts.

(See step 7 on pages

EM–95

to 101)

(b) Using a dial indicator, measure the thrust clearance

while moving the camshaft back and forth.

Standard thrust clearance: 0.040–0.090 mm

(0.0016–0.0035 in.)

Maximum thrust clearance: 0.12 mm (0.0047 in.)

If the thrust clearance is greater than maximum, replace the
camshaft. If necessary, replace the bearing caps and cylin-
der head as a set.

H.

Inspect camshaft gear backlash
(a) Install

the

camshafts

without installing the exhaust

camshaft sub–gear.
(See step 7 on pages

EM–95

to 101)

(b) Using a dial indicator, measure the backlash.

Standard backlash: 0.020–0.200 mm

(0.0008–0.0079 in.)

Maximum backlash: 0.30 mm (0.0188 in.)

If the backlash is greater than maximum, replace the cam-
shafts.

11. INSPECT VALVE LIFTERS AND LIFTER BORES

(a) Using a caliper gauge, measure the lifter bore diameter

of the cylinder head.

Lifter bore diameter: 31.000–31.016 mm

(1.2205–1.2211 in.)

(b) Using a micrometer, measure the lifter diameter.

Lifter diameter: 30.966–30.976 mm

(1.2191–1.2195 in.)

(c) Subtract the lifter diameter measurement from the lifter

bore diameter measurement.

Standard oil clearance: 0.024–0.050 mm

(0.0009–0.0020 in.)

Maximum oil clearance: 0.07 mm (0.0028 in.)

If the oil clearance is greater than maximum, replace the lifter.
If necessary, replace the cylinder head.

–

ENGINE MECHANICAL

Cylinder Heads

EM–87

12. INSPECT AIR INTAKE CHAMBER

Using a precision straight edge and feeler gauge, measure
the surfaces contacting the intake manifold for warpage.

Maximum warpage: 0.15 mm (0.0059 in.)

If warpage is greater than maximum, replace the chamber.

13. INSPECT

INTAKE

MANIFOLD

Using a precision straight edge and feeler gauge, measure
the surfaces contacting the cylinder head and air intake
chamber for warpage.

Maximum warpage: 0.15 mm (0.0059 in.)

If warpage is greater than maximum, replace the manifold.

14. INSPECT EXHAUST MANIFOLD

Using a precision straight edge and feeler gauge, measure
the surfaces contacting the cylinder head for warpage.

Maximum warpage: 1.00 mm (0.0394 in.)

If warpage is greater than maximum, replace the manifold.

15. INSPECT CYLINDER HEAD BOLTS

Using a vernier caliper, measure the thread outside diameter
of the bolt.

Standard outside diameter: 9.770–9.960 mm

(0.3846–0.3921 in.)

Minimum outside diameter: 9.60 mm (0.3780 in.)

If the diameter is less than minimum, replace the bolt.

EM–88

–

ENGINE MECHANICAL

Cylinder Heads

16. IF NECESSARY, REPLACE SPARK PLUG TUBE

GASKETS
(a) Bend the ventilation case claw installed on the cylinder

head cover to an angle of 905 or more.

(b) Using SST and a hammer, tap out the gasket.
SST 09550–10012 (09552–10010, 09560–10010)

(c) Using SST and a hammer, tap in a new gasket until its

surface is flush with the upper edge of the cylinder head
cover.

SST 09550–10012 (09552–10010, 09560–10010)
(d) Apply a light coat of MP grease to the gasket lip.
(e) Return the ventilation case claw to its original position.

ASSEMBLY OF CYLINDER HEADS

(See Components on page

EM–59

)

HINT:

•

Thoroughly clean all parts to be assembled.

•

Before installing the parts, apply new engine oil to all
sliding and rotating surfaces.

•

Replace all gaskets and oil seals with new ones.

1.

INSTALL SPARK PLUG TUBES
HINT: When using a new cylinder head, spark plug tubes
must be installed.
(a) Apply adhesive to the end of the spark plug tube.

Adhesive: Part No.08833–00070, THREE BOND 1324

or equivalent

(b) Using a wooden block and hammer, tap in a new spark

plug tube until there is 48.7–49.3 mm (1.917 –1.941 in.)
protruding from the camshaft bearing cap installation
surface of the cylinder head.

NOTICE: Avoid tapping a new spark plug tube in too far
by measuring the amount of protrusion while tapping.

–

ENGINE MECHANICAL

Cylinder Heads

EM–89