Yanmar 1GM User Manual page 85

SINGLE-CYLINDER ENGINES
79
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Valve Guide Replacement
1. Remove the rocker arms as previously described.
2. Remove the push rods and mark them so they can be
reinstalled in their original positions.
3. Inspect push rod ends for damage. Maximum allow-
able runout is 0.03 mm (0.0012 in.).
4. Reinstall the push rods by reversing removal proce-
dure. Adjust valve clearance as described in Chapter
Three.
PUSH RODS
The cylinder head is equipped with replaceable valve
guides (6, Figure 22). The intake and exhaust valve
guides are identical. Take the cylinder head to a dealership
or machine shop if valve guide replacement is required.
When installing the valve guides, the grooved end must
be toward the top of the cylinder head. The groove must
be flush with the head surface as shown in Figure 29.
8. Check each spring on a flat surface with a steel square.
See Figure 27. Slowly revolve the spring 360
0
and note
the space between the top of the coil and the square. If it
exceeds 1.4 mm (0.055 in.) at any point, replace the
spnng.
9. Check the valve guides (Figure 28) for wear and
looseness. Refer to Table 1 for valve guide specifications.
A loose valve guide must be replaced.
•..--......-__ Valve
spring
Valve key
Wear cap
/ Spring
retainer
Valve
guide
PISTON/CONNECTING ROD ASSEMBLY
6. Test the valve springs under load on a spring tester
(Figure 26). Replace any spring that does not meet the
specification in Table 1.
7. Inspect the valve seats. If worn or burned, they must be
reconditioned. This is a job for a dealer or machine shop,
although the procedure is described in this chapter.
Piston/Connecting Rod Removal
1. Remove the engine as described in this chapter.
2. Place a suitable container under the oil pan and remove
the drain plug. Let the crankcase oil drain, then reinstall
the drain plug.