LEXUS SC400 1991 Service Repair Manual

EG1KM±02
CYLINDER HEAD COMPONENTS
INSPECTION AND REPAIR
1. CLEAN TOP SURFACES OF PISTONS AND CYLINDERBLOCK
(a) Turn the crankshaft, and bring each piston to top dead center (TDC). Using a gasket scraper, remove all the carbon 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±compressed
air.
2. CLEAN CYLINDER HEAD
A. Remove gasket materialUsing a gasket scraper, remove all the gasket material from
the cylinder block contact surface.
NOTICE: Be careful not to scratch the cylinder block contact
surface.
B. Clean combustion chambers
Using a wire brush, remove all the carbon from the combus-
tion chambers.
NOTICE: Be careful not to scracth the cylinder block contact
surface.
C. Clean valve guide bushingsUsing a valve guide bushing brush and solvent, clean all the
guide bushings.
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D. Clean cylinder headUsing a soft brush and solvent, thoroughly clean the cylinder
head.
3. INSPECT CYLINDER HEAD
A. Inspect for flatness Using a precision straight edge and feeler gauge, measure
the surface 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.
B. Inspect for cracks Using 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 the valve head.
(b) Using a wire brush, thoroughly clean the valve.
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5. INSPECT VALVE STEMS AND GUIDE BUSHINGS
(a) Using a caliper gauge, measure the inside diameter of theguide bushing.
Bushing inside diameter:
6.010 ± 6.030 mm (0.2366 ± 0.2374 in.)
(b) Using a micrometer, measure the diameter of the valve stem.
Valve stem diameter:
Intake5.970 ± 5.985 mm (0.2350 ± 0.2356 in.)
Exhaust 5.965 ± 5.980 mm (0.2348 ± 0.2354 in.)
(c) Subtract the valve stem diameter measurement from the guide bushing inside diameter measurement
Standard oil clearance:
Intake0.025 ± 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.
6. IF NECESSARY, REPLACE VALVE GUIDE BUSHINGS
(a) Insert an old valve wrapped with tape into the valve guide bushing, and break off the valve guide bushing by hitting it
with a hammer. Remove the snap ring.
HINT: Wrap the tape approx. 8 mm (0.31 in.) from the valve
stem ends.
NOTICE: Be careful not to damage the valve lifter hole.
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(b) Gradually heat the cylinder head to 80 ± 100
C (176 ±
212
F).
(c) Using SST and a hammer, tap out the guide bushing. SST 09201±70010
(d) Using a caliper gauge, measure the bushing bore diameter of the cylinder head.
(e) Select a new guide bushing (STD or O/S 0.05).
Both intake and exhaust
 


Bushing bore diameter mm (in.)


Bushing size
 11.000 ± 11.027
(0.4331 ± 0.4341) Use STD
 


11.050 ± 11.077
(0.4350 ± 0.4361)


Use O/S 0.05
V00228
If the bushing bore diameter of the cylinder head is greater
than 11.027 mm (0.4341 in.), machine the bushing bore to
the following dimension:
11.050 ± 11.077 mm (0.4350 ± 0.4361 in.)
If the bushing bore diameter of the cylinder head is greater
than 11.077 mm (0.4361 in.), replace the cylinder head.
HINT: Different bushings are used for the intake and exhaust.
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(f) Gradually heat the cylinder head to 80 ± 100
C (176 ±
212
F).
(g) Using SST and a hammer, tap in a new guide bushing until the snap ring makes contact with the cylinder head.
SST 09201±70010
(h) Using a sharp 6 mm reamer, ream the guide bushing to obtain
the standard specified clearance (See step 5 above)
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:
44.55
(c) Check the valve head margin thickness.
Standard margin thickness:
1.0 mm (0.039 in.)
Minimum margin thickness: 0.5 mm (0.020 in.)
If the margin thickness is less than minimum, replace the
valve.
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(d) Check the valve overall length.
Standard overall length:Intake94.95 mm (3.7382 in.)
Exhaust 96.90 mm (3.8150 in.)
Minimum overall length:
Intake94.45 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 minimum.
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 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: wIf 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:
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 5 and 45 5
cutters to correct the seat.
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(2) If the seating is too low on the valve face, use 755 and
45 5 cutters to correct the seat.
(d) H and±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 deviation of the valve spring.
Maximum deviation:
2.0 mm (0.079 in.)
If the deviation 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:
186 ± 206 N (19.0 ± 21.0 kgf, 41.9 ± 46.3 lbf)
at 32.9 mm (1.295 in.)
If the installed tension is not as specified, replace the valve
spring.
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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 centerjournal.
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:
Intake41.710 ± 41.810 mm (1.6421 ± 1.6461 in.)
Exhaust 41.910 ± 42.010 mm (1.6500 ± 1.6539 in.)
Minimum cam lobe height: Intake41.56 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.
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D. Inspect camshaft bearingsCheck that bearings for flaking and scoring.
If the bearings are damaged, replace the bearing caps and
cylinder head a set.
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 Plasti gage across each of the camshaft
journals.
(d) Install the bearing caps. (See step 7 on pages EG±114 to 120)
Torque: 16 N Vm (160 kgf Vcm, 12 ft Vlbf)
NOTICE: Do not turn the camshaft.
(e) Remove the bearing caps.
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(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.
(h) Remove the camshafts.
G. Inspect camshaft thrust clearance
(a) Install the camshaft. (See step 7 on pages EG±114 to 120)
(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.
(c) Remove the camshafts.
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