Yanmar 2TNV70 Service Manual page 132

ENGINE
Inspection of Pistons, Piston Rings and
Wrist Pin
Notes:
• On an engine with low hours, the pistons, piston
rings may be reused if they are found to be within
specifications. The pistons and piston rings must
be reinstalled in the same cylinders from which
they were originally removed.
• On an engine with high hours, the pistons rings
should be replaced and the cylinder honed (See
Honing and Boring on page 6-51) or replaced.
The piston should be replaced as necessary.
1. Clean piston ring grooves using a piston ring
groove cleaning tool. Follow manufacturer's
instructions for correct operation.
2. Wash the pistons in an appropriate solvent
using a soft brush.
3. Visually inspect each piston for cracks. Pay
particular attention to the ring lands between
the piston ring grooves.
4. Measure the diameter of the piston skirt at 90°
to the wrist pin bore as shown (Figure 6-64).
Measurements must be taken at a specified
distance (Figure 6-64, (1)) from the bottom of
the piston, based on engine model. Record the
measurements. See Piston on page 6-9 for
specifications.
(1)
Figure 6-64
6-46
5. Subtract the piston measurement from the
greatest measurement acquired during cylinder
inspection (see Inspection of Cylinder Block on
page 6-45) to obtain piston-to-cylinder
clearance. Record the measurements. See
Piston on page 6-9 for specifications.
6. Measure the diameter of the wrist pin bore on
both sides of the piston (Figure 6-65). See
Piston on page 6-9 for specifications. Record
the measurements.
7. Measure the outside diameter of the wrist pin in
three places and at 90° (Figure 6-66). See
Piston on page 6-9 for specifications. Record
the measurements.
8. Using a micrometer, measure the thickness of
each piston ring. See Piston Ring on page 6-10
for specifications. Record the measurements.
Notes:
• On an engine with low hours, the pistons,
piston rings and cylinders may be reused if they
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are found to be within specifications.
Cylinder Block
Figure 6-65
Figure 6-66
TNV IDI Service Manual
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