Valve Guide Replacement - Honda 2010 CRF250R Service Manual

CYLINDER HEADNALVES
Refac6
the
valve
seals
whenever the
valve guides are
rep/aced
(page
8-23)
Measure and record each valve guide 1.0, tn the
combustion chamber.
SERVICE LIMIT:
IN : 5.052 mm (0.1989 in)
EX : 4.552 mm (0.1792 in)
Subtract each valve stem 0 .0. from the corresponding
guide 1.0. to obtain the slem-to-guide clearance.
STANDARD :
IN : 0.010 -
0.037 mm
(0.0004 - 0.001510)
EX: 0.020 - 0.047 mm (0.0008 - 0.0019 In)
If the stem.to-guide clearance exceeds the service
l_~~::'J~~~
limits, determine if a new guide with standard
dimensions would bring the clearance within tolerance.
If so, replace the guides as necessary and ream to fit.
If the slem-Io-guide clearance exceeds the service
limits
with
new guides also, replace the valves and
guides.
VALVE GUIDE REPLACEMENT
Be
sure to wear
heavy
gloves
when
handllfll} the heated
cylinder head.
Using
a
torch
ro
hear
the cylinder
head may
causa
warpage.
8-22
Mark new valve guides at the proper depth (see , - -
specification page 8-22) using a marker. Chill a new
valve guides in a freezer for about 1 hour.
Heal the cylinder head to 100 - 150~C (212 - 302°F)
with a hot plate or oven. Do not heat the cylinder head
beyond 160·C (320"F). Use temperature Indicator
sticks, available from welding supply stores, to be sure
the cylinder head is heated to the proper temperature.
Support the cylinder head and drive the valve guides
out of the cylinder head from the combustion chamber
side.
TOOLS :
IN : Valve guide driver,
5.0mm
EX:Valve guide driver,
4.Smm
07942-8920000 or
07942·MA60000
(U.S .A. only)
07HMH·ML00101
0'
07HMH·ML0010B
(U .S.A. only)
Adjust the valve guide driver to the valve guide height.
While the cylinder head is still heated, drive new valve
guides into the cylinder head from the top of the
cylinder (camshaft and rocker arm side).
Check that the valve guides are at the proper depth
using a caliper. adjust Ihe height if necessary.
SPECIFIED DEPTH :
IN : 1S.4-15.6 mm (0.606-0.61 4 in)
EX: 21.3 - 21 .5 mm (0.839 - 0.847 In)
TOOL:
Valve guide driver 07743"()020000
not ava ilable in
U.S.A.
let Ihe cylinder head cool 1 0 room temperature.