the valve guide if any measurement is outside the
specified range.
7. Subtract the valve stem outside diameter (Step 4)
from the valve guide inside diameter (Step 6). The
difference is the valve stem-to-guide clearance. If
the clearance exceeds the service limit, replace the
valve and valve guide.
NOTE
If a small bore gauge is unavailable,
perform Step 8 to check valve stem to
guide clearance. Measure the valve
stem diameter before performing this
test. This test is only accurate if the
valve stem is within specification.
8. Insert the valve into its guide and attach a dial in-
dicator as show in
Figure 89
. Hold the valve
slightly off its seat and rock it sideways in two di-
rections. Watch the dial indicator while rocking the
valve. Compare the valve movement to the valve
stem-to-guide clearance specification in
Table 2
. If
the movement is outside the specified range, the
valve guide should probably be replaced. As a final
check, take the head to a dealership and have the
valve guides measured.
9. Check the valve spring as follows:
a. Visually inspect the valve spring for bends or
other signs of distortion.
b. Measure each valve spring free length with a
vernier caliper (
Figure 90
). Replace the
spring if its free length is less than the service
limit.
c. Use a square to measure the tilt of each spring
(
Figure 91
). Tilt should be within the specifi-
cation in
Table 2
.
d. Replace any defective or worn spring.
10. Measure the valve margin thickness (
Figure
92
) with a vernier caliper. Replace the valve and
valve guide if the margin thickness is worn to the
wear limit.
11. Check the spring seat, spring retainer and valve
keepers for cracks or other damage.
12. Inspect each valve seat (
Figure 93
) in the cyl-
inder head. If a seat is burned or worn, it must be re-
conditioned. This should be performed by a
dealership or local machine shop. Seats and valves
in near perfect condition can be reconditioned by
lapping with fine carborendum paste, however, lap-
ping is inferior to precision grinding.
Valve Guide Replacement
Special tools
When valve stem-to-guide clearance is exces-
sive, the valve guides must be replaced. If a valve
guide is replaced, also replace its respective valve.
This procedure requires the following special tools
and should be entrusted to a Yamaha dealership or
other qualified specialist.
114
CHAPTER FOUR
88
89
Dial indicator
90