ENGINE REPAIR (Cont'd)
Valves
Small bums, grooves, etc., can be removed. Remove
valves that are damaged, if the surface alignment cannot
be corrected by finishing
or
if the valve stem clearance is
more than specifications allow.
Grinding Valves
If the valve surface alignment is not within specifications
grind the valve to a 45° angle. Remove only enough
material to correct the alignment
or
to make the surfaces
smooth. If the edge of the valve head is less than 1/32 inch
thick after grinding [A], install new valve as the old valve
wi" cause engine to run hot. Remove
a"
grooves
or
scratches from the end of the valve stem, and make
chamfer as needed.
DO NOT remove more than 0.010
inch (0,245 mm) from the end of the valve stem.
If
the valve
or
valve seat has been finished, it wi" be
necessary to check the clearance between the rocker
arm and the valve stem with the rocker assembly
installed
in
the engine.
Selecting Fitting Of The Valves
If the valve stem to valve guide clearance is more than the
wear limit, use a reamer to cut the valve guide to the next
oversize valve stem.
Valves with oversize stem diameters
of
0.003 inch, 0.015 inch and 0.030 inch are available as
service parts. Grind the valve seat after the valve guide
has been cut.
Camshaft Repair
Remove sma" marks from the camshaft machined
surfaces with a smooth oil stone.
Crankshaft
Remove small marks with an oil stone. If the journals are
damaged or worn, they must be machined to the correct
size for the next size smaller bearing.
Repairing Journals
After machining the bearing surfaces, put a chamfer
in
the
oil holes; then finish the bearing surfaces with a No. 320
grit cloth and engine oil. Crocus cloth may also be used
for finishing.
To Check Crankshaft Or Connection Rod Bearings
With Plastigage
Clean crankshaft bearing surfaces. Check the surfaces
and thrust bearings for damage. When making
replacement of standard size bearings, install bearing of
minimum specified clearance.
If the needed clearance
cannot be made with a standard bearing use a 0.002 inch
size
smaller
in
combination with a standard bearing to get
the correct clearance. (See SPEC/FICA TlONS Section
88-1
.)
Revised Oct. 97
-7B-15-
A
Check For
~
Bent
Stem
~
For Dimensions
Diameter
-.
Refer
To
Specifications
Valve
1/32" (0,79 mm)
Face
Minimum
Angle
~
/
t
'\
Critical Valve Dimensions
+
I
MC-011
03
741,742,743,
743DS Bobcat Loader
Service Manual
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