Yanmar 2TNV70 Service Manual page 112

ENGINE
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 6-5 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 valve 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 valve and rotate to distribute
bluing onto the valve face. The contact pattern
should be approximately centered on the valve face
(Figure 6-20, (1)) and even in width.
Figure 6-20
Also visually inspect the valve seat for even
contact.
Light cutting can be performed by the use of a
hand-operated cutter (Figure 6-21, (3)).
6-26
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 6-21, (1)) to specification. See
Cylinder Head on page 6-4 for the service limit.
Grind the valve face and / or valve seat only
enough to return them to serviceable condition.
Grinding is needed if the valve and the valve seat
do not contact correctly. Check the valve recession
after grinding.
If the valve or seat require grinding, lap the valve
after grinding. Lap the valve face to the valve seat
using a mixture of valve lapping compound and
engine oil.
Be sure to thoroughly wash all parts to remove all
grinding powder or compound.
Inspection of Valve Springs
Inspect the valve springs. If damage or corrosion is
seen, or if measurements exceed the specified
(1)
limits, replace the springs. Record the
measurements.
Fractures
0001691B
Check for fractures on the inside and outside
portions of the springs. If the valve spring is
fractured, replace the valve spring.
Corrosion
Check for corrosion of spring material caused by
oxidation.
(1)
150°
40°
(2)
Figure 6-21
TNV IDI Service Manual
Cylinder Head
(3)
0001862