Yanmar 1GM User Manual page 117

MULTICYLINDER ENGINES
't----~-~Deburr
--.ii-----
Valve stem
t
Valve head thickness
111
Valve Removal
Refer to Figure 18 for this procedure.
1. Remove the cylinder head as described in this chapter.
2. Remove the rocker shaft assembly as described in this
chapter.
3. Remove the wear cap (1, Figure 18) on the valve stem.
4. Compress the valve spring with a compressor like the
one shown in Figure 19.
5. Remove the valve keys (2, Figure 18) and release the
spring tension.
6. Remove the valve spring retainer and valve spring.
CAUTION
Remove any burrs from the valve stem lock
grooves (Figure 20) before removing the
valve to prevent damage to the valve guide.
7. Remove the valve.
8. Remove and discard the valve stem seal (5, Figure
18).
9. Repeat Steps 3-8 for the remaining valves.
Inspection
1. Clean the valves with a fine wire brush or buffing
wheel. Discard any cracked, warped or burned valves.
2. Measure the valve stems at the top, center and bottom
for wear. A machine shop can do this when the valves are
ground.
NOTE
Check the thickness of the valve edge or
margin after the valves have been ground.
See Figure
21.
Any valve with a margin less
than 0.75 mm (0.030 in.) should be dis-
carded.
3. Remove all carbon and varnish from the valve guides
with a stiff spiral wire brush.
NOTE
The next step assumes that all valve stems
have been measured and are within specifi-
cations. Replace valves with worn stems be-
fore performing this step.
4. Insert each valve into the guide from which it was re-
moved. Holding the valve just slightly off its seat, rock it
back and forth in a direction parallel with the rocker arms.
This is the direction in which the greatest wear normally
occurs. If the valve stem rocks more than slightly, the
valve guide is probably worn.
5. If there is any doubt about valve guide condition after
performing Step 4, measure the valve guide. Compare the