Honda NSS250A Reflex 2001-2007, Manual

Page: 309 / 718

CYLINDER HEAD/VALVES
9-15
Measure each valve guide I.D. and record it.
Subtract each valve stem O.D. from the correspond-
ing guide I.D. to obtain the stem-to-guide clearance.
If the stem-to-guide clearance exceeds the service
limit, determine if a new guide with standard
dimensions would bring the clearance within toler-
ance.
If so, replace any guides as necessary and ream to
fit.
If the stem-to-guide clearance exceeds the service
limit with new guide, also replace the valve.
CAM CHAIN GUIDE/CAM CHAIN TENSIONER
Remove the cam chain tensioner (page 9-11).
Check the cam chain guide and cam chain tensioner
for wear or damage, then replace them if necessary.
VALVE GUIDE REPLACEMENT
Chill the new valve guides in a freezer for about 1
hour.
Heat the cylinder head to 100 – 150
°
C (212 – 302
°
F)
with a hot plate or oven. Use temperature indicator
sticks, available from welding supply stores, to be
sure the cylinder head is heated to the proper tem-
perature.
Support the cylinder head and drive the valve
guides out of the cylinder head from the combus-
tion chamber side.
Take out new valve guides from the freezer.
Drive new valve guides into the cylinder head to the
specified height from the cylinder head.
Let the cylinder head cool to room temperature.
SERVICE LIMIT: IN/EX: 4.54 mm (0.179 in)
SERVICE LIMITS:
IN: 0.08 mm (0.003 in)
EX: 0.09 mm (0.004 in)
Inspect and reface
the valve seats
whenever the valve
guides are replaced
(page 9-15).
CAM CHAIN TENSIONER
CAM CHAIN GUIDE
Be sure to wear
heavy gloves to
avoid burns when
handling the heated
cylinder head.
Using a torch to
heat the cylinder
head may cause
warpage.
TOOL:
Valve guide driver, 4.3 mm
07HMD-ML00101
VALVE GUIDE DRIVER
Drive new guides
from the camshaft
side while the
cylinder head is still
heated.
TOOL:
Valve guide driver
07743-0020000
VALVE GUIDE PROJECTIONS:
IN: 11.2 – 11.5 mm (0.44 – 0.45 in)
EX: 12.2 – 12.5 mm (0.48 – 0.49 in)
VALVE GUIDE DRIVER
INSTALLED
LENGTH
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