Toyota Supra 1990 Manual page 75

ENGINE MECHANICAL - Cylinder Head
EM-43
EM2586 EM2938
EM2588 EM2589
7. INSPECT CYLINDER HEAD FOR CRACKS
Using a dye penetrant, check the combustion chamber, in-
take and exhaust ports, head surface and the top of the
head for cracks.
If cracked, replace the head.
8. CLEAN VALVES
9.
(a) Using a gasket scraper, chip any carbon from the valve
head.
(b) Using a wire brush, thoroughly clean the valve.
INSPECT VALVE STEMS AND GUIDE BUSHINGS
(a) Using a caliper gauge, measure the inside diameter
of the valve guide bushing.
Guide inside diameter: 6.010 - 6.030 mm
(0.2366 - 0.2374
in.)
(b) Using a micrometer, measure the diameter of the valve
stem.
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 the valve stem diameter measurement from
the valve guide bushing inside diameter measurement.
Standard stem
oil
clearance:
Intake 0.025 - 0.060 mm
(0.0010 - 0.0024 in.)
Exhaust
0.030 - 0.065 mm
(0.0012 - 0.0026 in.)
Maximum stem 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.