Volvo Penta TAD1630G, Workshop Manual

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Group 21 Service procedures - engine
43
Pistons, checking
Check the pistons for cracks and other damage. If the piston
has deep lines around the sleeve surface it (liner unit) must
be scrapped. Similarly, if the piston has one or several
cracks in the gudgeon pin hole or in the bottom of the com-
bustion chamber it shall also be scrapped. Cracks in the
edge of the piston top around the combustion chamber are
not serious as a rule. The crack test is carried out as per the
powdered lime method.
Note: If cracks are found in the pistons the fuel injection vol-
ume should also be checked.
Pistons, fitting
Like the cylinder liners, the pistons are classified, this mean-
ing that a certain class of piston can only be used in an
equivalent class of cylinder liner. The piston and cylinder lin-
er sets are only available from stock as a single, complete
unit.
Piston rings, inspection
Check the wear surfaces and sides. Black spots on the sur-
faces point to poor contact, in which case the piston rings
should be replaced. Piston rings should also be replaced if
there is noticeable wear or the cylinders are out of round,
since very often the rings do not take up the same position
they had prior to removal. Oil consumption is also a matter of
significant importance concerning the time at which piston
rings should be replaced.
Connecting rods, inspection
Check for cracks. Check straightness and warping. Warped
or twisted connecting rods should be scrapped. Check the
connecting rod bushings, this is best done using a new
gudgeon as a gauge. There should be no noticeable play.
Measuring is carried out in a fixture for checking connect-
ing rods.
Straightness, max deviation 0.05 mm (0.0020") on a
length of 100 mm (3.94").
Warp, max deviation 0.1 mm (0.0039") on a length of
100 mm
Connecting rod bushings,
replacing
When replacing connecting rod bushings in a connecting rod
of trapezoidal shape, the bushing must be line bored.
The bushing must be bored to give a fit which with the gudg-
eon pin oiled allows the pin to slide through slowly of its own
weight (temp. 17-20°C (63-68°F).
Following line boring, the connecting rods should be meas-
ured in the fixture to check that the hole in the bushing is
placed correctly in the connecting rod.