Yanmar 4TNV98, Service Manual

Page: 98 / 246

4TNV98 & 4TNE98 Diesel Engine Section 3. Engine 96
Figure 6-56
Valve Face and Valve Seat
Always check the clearance between the valve and
valve guide before grinding or lapping the valve
seats. See Intake/Exhaust Valve and Guide on page
67 for the service limit. If the clearance exceeds the
limit, replace the valve and/or valve guide to bring
the clearance within the limit.
Roughness or burrs will cause poor seating of a
valve. Visually inspect the seating surfaces of each
valve and valve seat to determine if lapping or
grinding is needed.
Visually inspect all valves faces and valve seats for
pitting, distortion, cracking, or evidence of
overheating. Usually the valves and valve seats can
be lapped or ground to return them to serviceable
condition. Severely worn or damaged components
will require replacement.
Coat the valve seat with a thin coat of bluing
compound. Install the valve and rotate to distribute
bluing onto the valve face. The contact pattern
should be approximately centered on the valve face
(Figure 6-57, (1)) and even in width.
Figure 6-57
Also visually inspect the valve seat for even contact.
Light cutting can be performed by the use of a hand-
operated cutter
(Figure 6-58) .
Figure 6-58
Valve seat diameter can be adjusted by top-grinding
with a 150° stone to make the seat diameter smaller,
and bottom-grinding using a 40° stone to make the
seat diameter larger. Once the seat location has
been corrected, grind and lap the seat angle
(Figure
6-58, (1)) to specification. See Cylinder Head on
page 66 for specifications.