Yanmar 1GM User Manual page 84

78
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Deburr
Valve stem
5. Remove the valve keys (2, Figure 22) 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 24) 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
22).
9. Repeat Steps 3-8 for the remaining valve.
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 25. 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.
CHAPTER FIVE
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45°
I Valve head thickness }
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
results with specifications in Table 1. Worn guides must
be replaced.