66 SEBU8191-01
Maintenance Section
Overhaul (Top End)
•
Engine mounted
aftercoolers
•
Camshafts
•
Camshaft followers
•
Connecting r
ods and bearings
•
Crankshaft and bearings
•
Gear train
•
Inlet air pi
ping
•
Oil cooler
•
Pistons and rings
•
Cylinder l
iners
Replace the crankshaft vibration damper.
i04328053
Overhaul (Top End)
Schedu
ling a Top End O verhaul
Top end overhauls should be scheduled according to
the rec
ession of the valve stems. This measurement
provides an accurate indication of the rate of valve
wear. This measurement can be used to predict when
a cyli
nder head requires replacement.
Note: Generally, cylinder heads wear out at different
rate
s. In some cases, servicing the cylinder heads at
different times may be the most economic decision.
This depends on the valve stem projection of the
indi
vidual cylinders. However, this decision must
include the costs of additional downtime that is
caused by this procedure. Perform an economic
anal
ysis in order to determine if cylinder heads should
be serviced as a group or divided into smaller groups.
Top End Overhaul I nfor mation
Ato
p end overhaul involves servicing the cylinder
heads. During a top end overhaul, one piston should
be removed. Inspect the piston, piston rings, and the
cy
linder liner. The condition of these components will
determine the period of the major overhaul. Refer to
Service Manual for more information.
Monitoring Valve Seat Wear
E
very 500 service hours record the valve lash. The
monitoring of the valve seat wear should be carried
out before any adjustment of the valve lash.
1. Remove the rock
er covers.
2. Refer to Systems Operation, Testing and
Adjusting, “V
alve Lash - Adjust”.
3. On all engine cylinders, record the clearance
before any ad
justments are made.
4. Set the valve bridges.
5. Adjust the valve lash to 0.4 mm (0.016 inch).
The recorde
d values can be used to identify any
excessive valve seat wear on individual valves. The
recorded values can be used to schedule a top end
overhaul.
An example of recorded valve lash
Table 23
Recorded
clearances on A1
cylinder
Total va l
ve wear
Hours Inlet Exhaust Inlet Exhaust
500 0.4mm 0.4mm 0 0
1000 0.4 0.4 0 0
1500 0.35 0.35 0.05 0.05
2000 0.35 0.35 0.1 0.1
2500 0.3 0.3 0.2 0.2
3000 0.25 0.3 0.35 0.3
3500 0.25 0.35 0.5 0.35
4000 0.25 0.3 0.65 0.45
After 4000 hours running, the valve seat wear on
the inlet is 0.65 mm (0.026 inch) and the exhaust is
0.45
mm (0.018 inch).
Note: Maximum permitted valve seat wear is
1.0
0 mm (0.040 inch).
In this example, the valves are still serviceable after
400
0 hours running.
When the valves approach the maximum wear limit,
th
e rockers can be removed and a measurement
fromthecylinderheadfacetothetopofthevalve
stems can be taken. When a new valve is installed
th
e protrusion of the valve stem would be 29.75 mm
(1.171 inch). therefore, a maximum wear limit would
be 30.75 mm (1.211 inch).
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