DeWalt DW168F - Page 45

45
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If the stem to guide clearance exceeds the service limit:
Determine if the new guide with standard dimensions would bring the clearance within tol-
erance, if so replace any guide as necessary and ream to fit. If the stem to guide clearance
exceeds the service limit with new guides, replace the valves also.
NOTE: Recondition the valve seats when valve guides are replaced.
VALVE GUIDE REPLACEMENT
1. Drive the valve guides out of the head from
the combustion chamber side using a
valve guide driver.
2. Install the new valve guides from the
valve spring side of the cylinder head.
Exhaust side: Drive the exhaust valve
guide until the clip is fully seated as
shown.
Intake side: Drive the intake valve
guide to the specified height (measure
from the top of the valve guide to the
cylindercastingasshown)
IN valve guide
installation height
3.0mm(0.12")
3. After installation, inspect the valve guide
IN: 3.0 mm
.012 in
EX: CLIP
for damage, replace if necessary.
VALVE GUIDE REAMING
1. Coat the reamer and valve guide with
cutting oil.
 2.Rotate the reamer clockwise through
the valve guide the full length of the
reamer.
 3.Continuetorotatethereamerclockwise
while removing it from the valve guide.
4. Thoroughly clean the cylinder head
to remove any cutting oil residue and
chips.
 5.Check thevalveguide bore: it should
be straight, round and centered in
the valve guide. Insert the valve and check operation. If the valvedoes not operate
smoothly, the guide may have been bent during installation. Replace the valve guide if
it is bent or damaged.
 6.ChecktheValveGuidetoStemClearance.
VALVE SEAT RECONDITIONING
1. Clean the combustion chamber and valve
seats(V8)toremovecarbondeposits.
2. Apply a light coat of Prussian Blue or eras-
ablefelt-tippedmarkeronvalveface.
3. Insert the valve and snap it closed against
the seat several times. Ensure the valve does
notrotateontheseat.Thetransferredmark-
ing compound will show any area of the seat
this is not concentric.
NOTE: Follow the valve seat cutter manufacture
instructions.
4. Use a 45° cutter to remove enough material
to produce a smooth and concentric seat.
  Turn the cutter clockwise, never counterclockwise.
Continue to turn the cutter while lifting it from the valve
seat.
5. Use a 30° – 32° and 60° cutter to narrow and adjust the
valve seat so it contacts the middle of the valve face.
Use a 30° – 32° cutter to remove material from the
bottomedge(contacttoolow).
Use a 60° cutter to remove material from the top edge
(contact too high). Ensure the width of the finished
valve seat is within specifications.
V8
VALVE
SEAT
CUTTER
VALVE
GUIDE
DRIVER
REAMING TOOL
VALVE
GUIDE
CORRECT
INCORRECT