Westerbeke 6.5 MCG Service Manual page 24

PISTONS AND CONNECTING RODS
PISTON PIN INSPECTION
Reinsert the piston pin into the piston hole with your
thumt>~
You should feel a slight' resistance, if the bore is misaligned·
the pin will click or bind as it enters. Try the pin from both
· sides. Replace the piston if the pin can be too easily inserted
or if there is excessive play.
NOTE: The piston pin
and
piston are replaced as an assembly.
Measure the outside diameter of the piston pin.
PISTON PIN 0.0.0.&300 • 0.&3021n (16.001·16.007mm)
Pistons
Check the piston surfaces for wear, seizure, cracks and
streaking. If any damage is evident, replace the piston.
Inspect the oil return hole in the oil ring groove and the oil
hole in the piston boss. Clean the piston if these are clogged.
Check
the
piston pin hole for signs of seizure or damage.
Replace
the
piston if damage is evident Measure the piston
diameter
at
90° (perpendicular) to the pin bore axis.
PISTON 0.0.2.5579 • 2.559110 (64.97 • 65.00mm)
If the piston diameter is less then the standard replace
the piston.
NOTE: The piston
and
piston pin are replaced as an assembly.
Piston Rings
Insert the piston ring into the cylinder bore placing
it
against
the top of the piston head and pressing it in. When it marks a
right angle, measure the piston ring gap with a feeler gauge.
When the gap is too large, replace the piston ring.
PISTON RING GROOVE
standard
No.1 0.0480 • 0.04881n (1.22 ·1.24mm)
No 2 0.0476 • 0.0484ln (1.21 ·1.23mm}
Oil 0.1108 • 0.1116in (2.815 • 2.835mm)
PISTON RING END GAP
No.1
No.2
Oil
PISTON
Sta~ilard
0.0059 • 0.01181n (0.15 • 0.3Dmm)
0.0138 • 0.0197in (0.35 • 0.50mm)
0.008- 0.028ln (0:2 • 0.7mm)
Limit
O.Bmm (0.0315in)
O.Bmm (0.0315in)
1..0111m
(0.03941~)
Check the piston ring for damage, wear, seizure and bends
replacing the rings if anything unusual is noted. Always
replace the piston rings when installing a new piston.
RING SIDE
CLEARANCE
FEELER GAUGE
Check the clearance between the piston ring and.
the
ring
groove, if it exceeds the limit, replace the rings, the piston
or both.
PISTON RING SIDE CLEARANCE
Standard limit
No.1 ring 0.0012 • O.OD28tn (0.03 • 0.07mm) 0.0047in (0.12mm)
No.2 ring 0.0008 • O.D024ln (0.02 • O.O&mm) 0.0039in (0.1Dmm)
Connecting Rod Bearing
Visually check the surface of the bearing. Replace those
which are lopsided, streaked or seized. When streaks or
seizure are excessive, check the crankshaft.
If
damage is
discovered on the crahkshaft, either replace it or reuse after
undersize machining. If the connecting rod bearing indicates
severe thermal damage, replace the bearing.
Measure the inner diameter of the connecting rod bearing
and the outer diameter of the crankshaft pin. If the gap (oil
clearance) exceeds the limit, replace the bearing, and, if nec-
essary, the crankshaft ... or undersize machine the crankshaft
and replace the bearings with an appropriate undersize type.
CONNECTING ROD BEARING OIL CLEARANCE
Standard limit
0.0008-0.0018 in (0.021.· (0.045 mm)
D.004in (0.1mm)
PISTON RING GAP Engines & Generators
22