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JD 6068 Engine - valves diagnostic operations
Remove engine valve assembly
Identify all parts for proper assembly in same location as removed.
Compress JDE138 Valve Spring Compressor (A) over valve. Remove retaining
locks (B). Remove valve spring compressor.
Remove valve rotators (A) and valve springs (B). Remove exhaust valve
stem shields. Remove valves (C) from JD 6068 cylinder head.
Inspect and Measure engine valve
Inspect and Measure JD 6068 engine valve springs - Inspect valve springs
for alignment, wear and damage. Put springs on a flat surface to see
that they are square and parallel. Check valve spring tension using
D01168AA Spring Compression Tester. Free spring length of 65 mm (2.56
in.) springs differ slightly, but compressed height must be the same.
VALVE SPRING SPECIFICATIONS
Spring Load Height Intake:
Open: 810—880 N (182—198 lb-force) - 38.1 mm (1.50 in.)
Closed: 345—399 N (78—90 lb-force) - 52.5 mm (2.07 in.)
Spring Load Height Exhaust:
Open: 797—867 N (179—195 lb-force) - 38.5 mm (1.52 in.)
Closed: 284—338 N (64—76 lb-force) - 54.5 mm (2.15 in.)
Inspect valve rotators and wear caps - Insure that valve rotators, if
equipped, will turn freely. Replace if defective. Replace valve wear
caps if pitted or worn. Inspect valve retainer locks for excessive wear.
Replace as needed.
Measure valve recess - Measure and record valve recess dimensions for
all valves and compare measurements to specifications given below.
Thoroughly clean all gasket material from cylinder head combustion face
before measuring.
VALVE RECESS SPECIFICATIONS
Valve Recess Below Cylinder Head:
Exhaust - 1.19—1.70 mm (0.047—0.067 in.) / Maximum Recess - 2.46 mm
(0.097 in.)
Intake - 3.35—3.86 mm (0.132—0.152 in.) / Maximum Recess - 4.62 mm
(0.182 in.)
If measurement does not meet specifications, check valve face angle and
valve seat angle. If valve is recessed beyond the maximum specification,
install either new valves, valve seat inserts, or both to obtain proper
valve recess.
Clean valves - Hold each valve firmly against a soft wire wheel on a
bench grinder. Make sure all carbon is removed from valve head, face and
unplated portion of stem.
Inspect and Measure John Deere 6068 engine valve - Thoroughly clean and
inspect valves to help determine if they can be restored to a
serviceable condition. Replace valves that are burned, cracked, eroded,
or chipped. Inspect valve retainer lock groove on valve stem for damage.
Also inspect stems for signs of scuffing, which may indicate
insufficient valve guide-to-valve stem clearance. Replace if defects are
evident. Measure valve head OD. Compare valve stem OD with guide ID to
determine clearance.
VALVE HEAD AND STEM SPECIFICATIONS
A—Valve Head OD:
Exhaust - 46.87—47.13 mm (1.845—1.856 in.)
Intake - 50.87—51.13 mm (2.003—2.013 in.)
B—Valve Stem OD:
Exhaust - 9.44—9.46 mm (0.3717—0.3724 in.)
Intake - 9.46—9.49 mm (0.3724—0.3736 in.)
Grind (reface) valves - Valve grinding should only be done by
experienced personnel familiar with equipment and capable of maintaining
required specifications. If necessary to reface valve, grind valve face
to an angle of 29.25° ± 0.25° (A). When valve faces are ground, it is
important not to nick valve head-to-stem radius with facing stone. A
nick could cause the valve to break. Radius all sharp edges after
grinding.
Measure valve guides - Measure valve guides for wear using a telescope
gauge and micrometer.
VALVE GUIDE SPECIFICATIONS
I.D. Guide in a New Head - 9.51—9.54 mm (0.3745—0.3755 in.)
New Guide-to-Valve Stem Clearance:
Exhaust - 0.051—0.102 mm (0.002—0.004 in.)
Intake - 0.025—0.076 mm (0.001—0.003 in.)
Worn guides can allow a clearance of 0.15 mm (0.006 in.) and still be
acceptable. Worn guides may be knurled to return them to specified
clearance if valve-to-guide clearance is 0.25 mm (0.010 in.) or less. If
clearance exceeds 0.25 mm (0.010 in.), install oversize valves. knurl
exhaust valve guides before reaming to assure proper valve guide-to-stem
clearance.
Remove valve seat insert and measure bores in cylinder head - In some
cases the inside diameter of the valve seat bore may become damaged or
oversized and require machining. In this case, oversize inserts are
available in 0.25 mm (0.010 in.) oversize only. Remove valve seat insert
(if necessary) with JDE41296 Valve Seat Puller. Adjusting screw on
puller may need to be retightened during removal of inserts.
On some John Deere engines, removal of valve seat inserts with the
JDE41296 Puller may not be possible. An alternate removal method is to
weld two or three short beads (use an arc welder) equidistant from each
other around the face of insert. Allow seat to cool and carefully pry
out the insert(s) with a screwdriver. If an arc welder is used to remove
valve seat inserts, protect entire combustion face and valve throat area
from weld spatter. After removal of inserts, thoroughly clean area
around valve seat bore and inspect for damage or cracks.
Install valve seat inserts - Install new or refaced valves and check
valve recess. Grind valve seats as required to maintain correct valve
recess and valve-to-seat seal.
Measure cylinder liner standout (height above block) - Bolt down liners
using cap screws and flat washers in the seven locations as shown. Flat
washers should be at least 3.18 mm (1/8 in.) thick. Tighten cap screws
to 68 Nm (50 lb-ft) to achieve an accurate standout reading.
Liners having obvious defects must be replaced. Variations in
measurement readings may occur within one cylinder and or between
adjacent cylinders. Measure each liner in four places, approximately at
1, 5, 7 and 11 O’clock positions as viewed from the rear of the engine
(flywheel end). Record all measurements by cylinder number. Remove any
liner that does not meet standout specification at any location and
install liner shims or replace piston/liner sets as necessary.
LINER HEIGHT SPECIFICATIONS
Liner Height Above Block - 0.050—0.127 mm (0.002—0.005 in.)
A—Cylinder Liner, B—Dial Indicator, C—Liner Height, D—Cylinder Block
Assemble engine valve assembly
Apply AR44402 Valve Stem Lubricant or clean engine oil to valve stems
and guides. Exhaust valve stem shields will not seat on valve guide
tower; they ride up and down with valve stem. Install reconditioned or
new valves in head. If valves are reused, install in same location from
which removed. Valves must move freely and seat properly. There is no
top or bottom to valve springs; they may be installed either way.
Position valve springs (B). End of spring must be in machined
counterbore of head. Do not mix valve springs. Install valve rotators
(A) on springs and valves (C). Install valve stem shields on exhaust
valve stems.
Compress valve springs with JDE138 Valve Spring Compressor (A) and
install retainer locks (B). Install wear caps just before installing
rocker arm assembly.
Strike end of each valve with a soft mallet three or four times to
insure proper seating of the retainer locks. Repeat procedure for all
remaining valves. Remember valve stem seals are installed onto exhaust
valve stems only. Measure valve recess.
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