Yanmar 3TNV82A-B Service Manual page 215

Crankshaft and Camshaft Components
Measure Crankshaft Bearing Oil Clearance
Oil clearance should be checked during
disassembly to determine the extent of wear, and
during assembly to ensure long engine life. The
same procedure is done for both connecting rods
and main bearings.
Inspection of Cylinder Block
1. Ensure that oil passages are clear and
unobstructed.
2. Check for discoloration or evidence of cracks. If
a fracture is suspected, use the color check
method or the Magnaflux method to determine
if the cylinder block is fractured.
3. Inspect cylinders for roundness, taper, or
evidence of scoring. Collect and record the
measurements. Consider honing, reboring or
replacing the cylinder block if the
measurements are not within specification.
• Take measurements at three places
(Figure 6-113) (a, b, c), and in two directions (d
and e) in each cylinder.
a
b
c
20 mm
(0.75 in.)
Figure 6-113
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.
TNV DI Service Manual
20 mm
(0.75 in.)
d
e
0000230B
• On an engine with high hours, the pistons rings
should be replaced and the cylinder honed
(See Honing and Boring on page 6-88) 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 6-114).
Measurements must be taken at a specified
distance (Figure 6-114, (1)) from the bottom of
the piston, based on engine model. Record the
measurements. See Piston on page 6-16 for
specifications.
(1)
Figure 6-114
5. Subtract the piston measurement from the
greatest measurement acquired during cylinder
inspection (see Inspection of Cylinder Block on
page 6-83) to obtain piston-to-cylinder
clearance. Record the measurements. See
Piston on page 6-16 for specifications.
6. Measure the diameter of the wrist pin bore on
both sides of the piston (Figure 6-115). See
Piston on page 6-16 for specifications. Record
the measurements.
ENGINE
0000235
6-83