9.9
Section 9
Inspection and Reconditioning
9
Piston Ring
Piston Ring
Expander
Replacement pistons are available in STD bore size,
and 0.25 mm (0.010 in.) oversize. Replacement pistons
include new piston ring sets and new piston pins.
Replacement ring sets are also available separately for
STD, and 0.25 mm (0.010 in.) oversize pistons. Always
use new piston rings when installing pistons. Never
use old rings.
Some important points to remember when servicing
piston rings:
1. The cylinder bore must be de-glazed before
service ring sets are used.
2. If the cylinder bore does not need re-boring and
if the old piston is within wear limits and free
of score or scuff marks, the old piston may be
reused.
3. Remove the old rings and clean up the grooves.
Never reuse old rings.
4. Before installing the new rings on the piston,
place the top two rings, each in turn, in its
running area in the cylinder bore and check the
end gap. (See Figure 9-8.) Compare the ring gap
to the measurments in Section 1, Specifications
and Tolerances.
Figure 9-8. Measuring Piston Ring End Gap.
5. Aer installing the new compression (top and
middle) rings on the piston, check the piston-
to-ring side clearance. Compare the clearance to
specifications listed in Section 1, Specifications
and Tolerances. If the side clearance is greater
than specified, a new piston must be used. Refer
to Figure 9-9.
Figure 9-9. Measuring Piston Ring Side Clearance.
Install New Piston Rings
To install new piston rings, proceed as follows:
NOTE: Rings must be installed correctly. Ring
installation instructions are usually included
with new ring sets. Follow instructions
carefully. Use a piston ring expander to
install rings (see Figure 9-10). Install the
boom (oil control) ring first and the top
compression ring last. Refer to Figure 9-11.
Figure 9-10. Installing Piston Rings.
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