1991 LEXUS SC300 oil

40. DISCONNECT MAIN HEATED OXYGEN SENSORCONNECTORS
Disconnect the RH and LH oxygen sensor connectors.
41. REMOVE CYLINDER HEADS
(a) Uniformly loosen the ten cylinder head bolts one side of each
cylinder head in several passes, in the sequence shown,
then do the other side as shown. Remove the 20 cylinder
head bolts and plate washers.
NOTICE:
w Cylinder head warpage or cracking could result from
removing bolts in incorrect order.
w Do not drop the plate washer for cylinder head bolt into
portion A of the cylinder head. If dropped into portion A,
the plate washer will pass through the cylinder head and
cylinder block into the oil pan.
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1UZ±FE ENGINE ENGINE MECHANICALEG±91
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(b) Remove the following parts:(1) Spring retainer
(2) Valve spring
(3) Valve
(4) Spring seat
HINT: Arrange the valves, valve springs, spring seats and
spring retainers incorrect order.
(c) Using needle±nose pliers, remove the oil seal.
EG±94
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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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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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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.
EG±102
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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.
EG±104
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H. Inspect camshaft gear backlash
(a) Install the camshafts without installing the exhaust camsub±gear.
(See step 7 on pages EG±114 to 120)
(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 then maximum, replace the cam-
shafts.
(c) Remove the camshafts.
11. INSPECT VALVE LIFTERS AND LIFTER BORES
(a) Using a caliper gauge, measure the ufter bore diameter of the
clinder 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 borediameter 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.
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