Yanmar 4TNV98, Service Manual

Page: 97 / 246

4TNV98 & 4TNE98 Diesel Engine Section 3. Engine 95
If distortion exceeds the service limit, resurface or
replace the cylinder head. Remove only enough
material to make the cylinder head flat, but do not
remove more than 0.008 in (0.20 mm).
Inspection of Intake and Exhaust Valves
Visually inspect the intake and exhaust valves.
Replace any valves that are obviously discolored,
heavily pitted or otherwise damaged.
Valve Stem Diameter
Use a micrometer to measure the valve stem
diameter. Measure the valve stem near the
combustion end and near the opposite end (Figure
6-53, (1)). See Intake/Exhaust Valve and Guide on
page 67 for the service limit.
Figure 6-53
Valve Stem Bend
Place the valve stem on a flat inspection block or
layout bed. Roll the valve until a gap can be
observed between a portion of the valve stem and
the surface of the block or bed. Use a feeler gauge
to measure the gap
(Figure 6-54) . See
Intake/Exhaust Valve and Guide on page 67 for the
service limit.
Figure 6-54
Valve Recession
NOTE : The valve guides must be installed to
perform this check.
Insert the valves into their original locations and
press them down until they are fully seated. Use a
depth micrometer
(Figure 6-55) to measure the
difference between the cylinder head gasket surface
and the combustion surface of each exhaust and
intake valve
(Figure 6-56) . See Cylinder Head on
page 66 for the service limit.
Figure 6-55
NOTE : 2-Valve cylinder head is shown. 4-Valve
cylinder head is similar.