Yanmar 4TNE98, Service Manual

Page: 99 / 246

4TNV98 & 4TNE98 Diesel Engine Section 3. Engine 97
Grind the valve face and/or valve seat as necessary
to return them to serviceable condition. Grinding is
needed if the valve and valve seat do not contact
correctly. Check the valve margin and 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 limits,
replace the springs.
Fractures
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.
Squareness
Use a flat surface and a square to check each
spring for squareness
(Figure 6-59) . See Valve
Spring on page 68 for the service limit.
Figure 6-59
Free Length
Use a caliper to measure the length of the spring
(Figure 6-60) . See Valve Spring on page 68 for the
service limit.
Figure 6-60
Inspection of Valve Bridges
4TNV98 Engine Only
Visually inspect the contact surface at both ends of
the valve bridge
(Figure 6-61, (2)) for excessive
wear or mushrooming.
Remove and inspect the seat
(Figure 6-61, (1)) .
Measure the diameter of the valve bridge guide pin
bore in the valve bridge and guide pin
(Figure 6-61,
(3)) . See Rocker Arm and Shaft on page 68 for the
service limit.
Figure 6-61