Refer to “cylinder head disassembly and assembly” .
Cylinder head distortion
Take clearance readings at several places. If readings exceed the service limit, replace the cylinder head.
Special tool
: 09900–20803 (thickness gauge)
Cylinder head distortion service limit: 0.02 Mm (0.0008 In)
Valve stem runout
Support the valve using v-blocks, as shown in the figure, and check its runout using the dial gauge. If the runout exceeds the service limit, replace the valve.
Special tool
(a): 09900–20607 (dial gauge)
(b): 09900–20701 (dial gauge chuck)
(c): 09900–21304 (v blocks)
Valve stem runout (in. & Ex.) Service limit: 0.05 Mm (0.002 In)
Valve head radial runout
Place the dial gauge at a right angle to the valve head face and measure the valve head radial runout. If it measures more than the service limit, replace the valve.
Special tool
(a): 09900–20607 (dial gauge)
(b): 09900–20701 (dial gauge chuck)
(c): 09900–21304 (v blocks)
Valve head radial runout (in. & Ex.) Service limit: 0.03 Mm (0.001 In)
Valve stem and valve face wear condition
Visually inspect each valve stem and valve face for wear and pitting. If it is worn or damaged, replace the valve with a new one.
Valve stem deflection
Lift the valve about 10 mm (0.39 In) from the valve seat.
Measure the valve stem deflection in two directions, “x” and “y”, perpendicular to each other. Position the dial gauge as shown. If the deflection exceeds the service limit, then determine whether the valve or the guide should be replaced with a new one.
Special tool
(a): 09900–20607 (dial gauge)
(b): 09900–20701 (dial gauge chuck)
Valve stem deflection (in. & Ex.) Service limit: 0.25 Mm (0.010 In)
Valve stem wear
Measure the valve stem o.D. Using the micrometer. If it is out of specification, replace the valve with a new one.
If the valve stem o.D. Is within specification but the valve stem deflection is not, replace the valve guide. After replacing the valve or valve guide, recheck the deflection.
Special tool
(a): 09900–20205 (micrometer (0 – 25
mm))
Valve stem o.D.
Standard (in.): 4.475 – 4.490 Mm (0.1762 – 0.1768 In) standard (ex.): 4.455 – 4.470 Mm (0.1754 – 0.1760 In)
Note if valve guides have to be removed for replacement after inspecting related parts, carry out the steps shown in valve guide replacement. Refer to “valve guide replacement” . |
Valve spring
The force of the coil springs keep the valve seat tight. A weakened spring results in reduced engine power output and often accounts for the chattering noise coming from the valve mechanism.
Check the valve springs for proper strength by measuring their free length and also by the force required to compress them. If the spring length is less than the service limit or if the force required to compress the spring does not fall within the specified range, replace both the inner and outer springs as a set.
Special tool
(a): 09900–20102 (vernier calipers
(200 mm))
Valve spring free length (in. & Ex.) Service limit: inner: 30.1 Mm (1.19 In) service limit: outer: 35.3 Mm (1.39 In)
Valve spring tension (in. & Ex.) Standard: inner: 31.3 – 38.3 N (3.2 – 3.9 Kgf, 7.0 – 8.6 Lbs)/27.55 Mm (1.085 In) standard: outer: 91.3 – 105.1 N (9.3 – 10.7 Kgf, 20.5 – 23.6 Lbs)/33.05 Mm (1.301 In)
Valve seat width
Caution do not use lapping compound. |
Special tool
(a): 09916–10911 (valve lapper set)
If the seat width “a” measured exceeds the standard value, or seat width is not uniform reface the seat using the seat cutter. Refer to “valve seat repair” .
Valve seat width “a” (in. & Ex.) Standard: 0.9 – 1.1 Mm (0.035 – 0.043 In)
Valve seat sealing condition
![]() extreme caution when handling gasoline. |
Note after servicing the valve seats, be sure to check the valve clearance after the cylinder head has been reinstalled. Refer to “valve clearance inspection and adjustment” in section 0b . |
Rear brake light switch inspection
Inspect the rear brake light switch in the following
procedures:
lift and support the fuel tank. Refer to “fuel tank
removal and installation” in section 1g (page 1g-
9).
Disconnect the rear brake light switch lead wire
coupler (1).
Inspect the rear brake light swi ...
Special tools and equipment
Recommended service material
Note
required service material is also described in the following.
“Starter motor components”
Special tool
...
Crankcase breather (pcv) hose inspection
Inspect the crankcase breather (pcv) hose in the
following procedures:
lift and support the fuel tank with the prop stay.
Refer to “fuel tank removal and installation” in section 1g .
Inspect the crankcase breather (pcv) hose (1) for
wear and damage.
If it is worn or damaged ...