LEXUS SC400 1991 Service Repair Manual

B. Inspect for cranksUsing 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 thevalve 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 ofthe guide bushing.
Bushing inside diameter:
6.010±6.030 mm (0.2366±0.2374 in.)
(b) Using a micrometer, measure the diameter of the valvestem.
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 theguide 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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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 borediameter 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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(e) Using a sharp 6 mm reamer, ream the guide bushing toobtain 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 faceangle.
Valve face angle: 44.5 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.
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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: w If blue appears 360
around the face, the valve is
concentric. If not, replace the valve.
w If blue appears 360
around the valve seat, the
guide and face are concentric. If not, resurface the
seat.
w 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 5
and 45 5 cutters to correct the seat.
(2) If the seating is too low on the valve face, use 75 5
and 45 5 cutters to correct the seat.
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(d) Hand±lap the valve and valve seat with an abrasivecompound.
(e) After hand±lapping, clean the valve and valve seat.
9. INSPECT VALVE SPRINGS (a) Using a steel square, measure the squareness of thevalve 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 valvespring 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.
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B. Inspect cam lobesUsing 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 camshaftjournals.
(d) Install the bearing caps. (See step 2 on page EM±55)
Torque: 20 N Vm (200 kgf Vcm, 14 ft Vlbf)
HINT: Do not turn the camshaft.
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(e) Remove the bearing caps.
(f) Measure the Plastigage at its widest point.
Standard oil clearance: 0.035±0.072 mm(0.0014±0.0028 in.)
Maximum oil clearance: 0.10 mm (0.039 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.
F. Inspect camshaft thrust clearance (a) Install the camshafts.
(See step 2 on page EM±55)
(b) Using a dial indicator, measure the thrust clearancewhile moving the camshaft back and forth.
Standard thrust clearance: 0.080±0.190 mm
(0.0031±0.0075 in.)
Maximum thrust clearance: 0.30 mm (0.0118 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.
11. INSPECT VALVE LIFTERS AND LIFTER BORES (a) Using a caliper gauge, measure the lifter bore diameterof 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.)
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(c) Subtract the lifter diameter measurement from the lifterbore 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.
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 MANIFOLDS Using a precision straight edge and feeler gauge, measure
the surfaces contacting the cylinder head for warpage.
Maximum warpage: 0.8 mm (0.031 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: 10.8±11.0 mm
(0.425±0.433 in.)
Minimum outside diameter: 10.7 mm (0.421 in.)
If the diameter is less than minimum, replace the bolt.
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ASSEMBLY OF CYLINDER HEAD
(See Components on page EM±35)HINT:
wThoroughly clean all parts to be assembled.
w Before installing the parts, apply new engine oil to all
sliding and rotating surfaces.
w Replace all gaskets and oil seals with new ones.
1. INSTALL HEATER UNION HINT: When using a new cylinder head, heater union must be
installed.
(a) Apply adhesive to the end of the heater union as shownin the illustration.
Adhesive: Part No. 08833±00070, THREE BOND 1324 or equivalent
(b) Using a wooden block and hammer, tap in a new heater
union, leaving 73 mm (2.87 in.) protruding from the
cylinder head.
NOTICE: Do not tap it in too far.
2. INSTALL EGR COOLER Install a new gasket and EGR cooler with the eight bolts.
Torque: 14 N Vm (140 kgf Vcm, 10 ft Vlbf)
3. INSTALL ENGINE COOLANT TEMPERATURE SENSOR
AND SENDER GAUGE
Torque: 20 N Vm (200 kgf Vcm, 14 ft Vlbf)
4. INSTALL GROUND STRAP AND THROTTLE CABLE
BRACKET
5. INSTALL ENGINE HANGERS
Torque: 39 N Vm (400 kgf Vcm, 29 ft Vlbf)
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3. INSTALL VALVES(a) Install new oil seal on the valve guide bushing.
HINT: The intake valve oil seal is brown and the exhaust valve
oil seal is black.
(b) Install the following parts:(1) Valve
(2) Spring seat
(3) Valve spring
(4) Spring retainer
HINT: Install the valve spring, facing the painted mark up-
ward.
(c) Using SST, compress the valve spring and place the two
keepers around the valve stem.
SST 09202±70010
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