Valve Guide Replacement - Honda NSS250S Manual

Measure each valve guide I.D. and record it.
SERVICE LIMIT: IN/EX: 4.54 mm (0.179 in)
Subtract each valve stem O.D. from the correspond-
ing guide I.D. to obtain the stem-to-guide clearance.
SERVICE LIMITS:
IN: 0.08 mm (0.003 in)
EX: 0.09 mm (0.004 in)
If the stem-to-guide clearance exceeds the service
Inspect and reface
limit, determine if a new guide with standard
the valve seats
dimensions would bring the clearance within toler-
whenever the valve
ance.
guides are replaced
If so, replace any guides as necessary and ream to
(page 9-15).
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)
Be sure to wear
with a hot plate or oven. Use temperature indicator
heavy gloves to
sticks, available from welding supply stores, to be
avoid burns when
sure the cylinder head is heated to the proper tem-
handling the heated
perature.
cylinder head.
Using a torch to
Support the cylinder head and drive the valve
heat the cylinder
guides out of the cylinder head from the combus-
head may cause
tion chamber side.
warpage.
TOOL:
Valve guide driver, 4.3 mm
Take out new valve guides from the freezer.
Drive new valve guides into the cylinder head to the
Drive new guides
specified height from the cylinder head.
from the camshaft
side while the
TOOL:
cylinder head is still
Valve guide driver
heated.
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)
Let the cylinder head cool to room temperature.
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CYLINDER HEAD/VALVES
CAM CHAIN TENSIONER
VALVE GUIDE DRIVER
VALVE GUIDE DRIVER
INSTALLED
LENGTH
CAM CHAIN GUIDE
9-15