Specifications, Service and Repair of Farm and Lawn Tractors


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.


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 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.


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.


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 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.