Specifications, Service and Repair of Farm and Lawn Tractors


John Deere 6068 diesel - Cylinder head inspect and reassembly operations

Remove cylinder head

Remove rocker arm cover, if not previously done. Drain all engine oil and coolant. Disconnect turbocharger oil inlet line at turbocharger or oil conditioning housing. Remove water manifold (A) and all coolant piping. Remove turbocharger (B) and exhaust elbow (E). Remove air intake manifold (C). Remove exhaust manifold.

A—Water Manifold, B—Turbocharger, C—Intake Manifold, D—Aftercooler Assembly, E—Exhaust Elbow

Remove fuel injection lines (A) and nozzles (B). Remove rocker arm cover (C) and ventilator outlet hose assembly.

Remove six cap screws (A) and remove all four clamps (B). Lift rocker arm assembly up and remove. Remove wear caps from valve stems. Remove all 12 push rods and identify for reassembly.

Clean and inspect push rods as explained later in this group. Remove all 26 cylinder head cap screws. If cylinder head gasket failed, check and record each cylinder head cap screw torque before removing. Make a reference mark (in-line) on socket and cylinder head surface. Loosen cap screw at least 1/2 turn. Retighten cap screw (using torque wrench) until reference marks align, and record torque.

Remove cylinder head gasket. Inspect possible oil, coolant, or combustion chamber leaks. Also, check for evidence of incorrect or defective head gasket being used. Do not rotate crankshaft with cylinder head removed unless all cylinder liners are secured with cap screws and large flat washers as described later in this group.

Disassemble and inspect rocker arm shaft assembly

Make preliminary inspection during disassembly. Look for: Worn or scored rocker arms, shaft, and shaft support. Weak or broken springs. Lube oil restriction. Remove plugs and washers from ends of rocker arm shaft. Slide springs, rocker arms, and rocker arm supports off rocker arm shaft identifying their parts for reassembly in the same sequence they were in before disassembly. Inspect rocker arm shaft (A) for severe scratching, scoring, or excessive wear at points of rocker arm contact. Measure rocker arm and shaft. Compare with specifications given below.

Wear could indicate weak valve springs, bent push rods, or loose rocker arm shaft clamps.


Rocker Arm I.D - 19.07—19.10 mm (0.7507—0.7520 in.)
Rocker Arm Shaft O.D - 19.01—19.05 mm (0.7484—0.7500 in.)

Check rocker arm adjusting nut (C) and screw (B) for damage. Visually inspect rocker arm for hairline cracks. Replace if necessary. Be sure all oil holes in rocker arm shaft are clean and open. Clean all rocker arm parts with clean solvent. Dry with compressed air. Check for cups or concave wear on ends of rocker arms where they contact wear caps.

Examine spacer springs on shaft between rocker arms. Be sure they are strong enough to exert a positive pressure on rocker arms. If the rocker arm has been damaged by a valve failure, replace it and the push rods when replacing valves. Roll rocker arm shaft and push rods on a flat surface to check for bends or distortion. Replace parts as necessary.

Assemble and inspect rocker arm shaft assembly - Assemble parts on rocker arm shaft opposite removal procedure. Make sure rocker arm shaft end plugs are firmly seated against end of shaft, and washers are installed on shaft.

Inspect and clean cylinder head

Inspect all John Deere 6068 diesel cylinder head passages for restrictions. Heads with restricted or clogged passages can be cleaned by soaking them in a tank of hot caustic solution. Scrape all old gasket material from head. Use a powered wire brush to clean sealing surfaces. If cylinder head is not put in a chemical hot tank for cleaning, clean with solvent and a brush. Dry with compressed air and be sure to blow out all passages.

Check cylinder head combustion face flatness - Check cylinder head flatness using D05012ST Precision Straightedge and feeler gauge. Check lengthwise, crosswise, and diagonally in several places. If any measurement exceeds this specification, the cylinder head must be either resurfaced or replaced.


Maximum Out-of-Flat (Over Entire Length or Width) - 0.102 mm (0.0040 in.)
Straightness per any 305 mm (12 in.) Length - 0.025 mm (0.001 in.)

Measure cylinder head Thickness - Measure head thickness from valve cover gasket rail-to-combustion face. If cylinder head thickness is less than wear limit. Do not attempt to resurface. Install a new cylinder head. If necessary to resurface cylinder head, a maximum of 0.762 mm (0.030 in.) can be ground from new part dimension. Remove only what is necessary to restore flatness. After resurfacing, check flatness as described earlier and check surface finish on combustion face of head. Check valve recess after grinding. Valve seat or valve face may be ground to bring this characteristic within specification.


Thickness - 155.45—155.71 mm (6.120—6.130 in.)
Wear Limit - 154.69 mm (6.09 in.)
Combustion Face Surface Finish (AA) - 0.015—0.0028 mm (60—110 micro-in.)
Maximum Wave Depth - 0.008 mm (0.0003 in.)

Install cylinder head

Thoroughly inspect new cylinder head gasket for possible manufacturing imperfections. Return any gasket that does not pass inspection. Be sure cylinder head and block gasket surfaces are clean, dry, and free of any oil. Put a new head gasket on JD 6068 diesel cylinder block. Do not use sealant on gasket; install dry. If cylinder head is lowered onto cylinder block and you discover that the head is not positioned correctly on locating dowels, remove cylinder head and install a new gasket. Do not try to reposition cylinder head on the same gasket again since the fire ring will possibly be damaged. Lower cylinder head everly to correct position on block using appropriate lifting equipment. Make sure that head is positioned correctly over dowels.

Install rocker arm assembly - Install push rods (A) in holes from which removed. Install wear caps (B) on valves, making certain caps rotate freely. Make sure spring pin (A) engages with hole (B) in shaft. Install shaft clamps (B) and all six cap screws (A). Tighten cap screws to 75 Nm (55 lb-ft).

Complete final assembly of injection pump side - Adjust valve clearance as directed earlier in this group. Apply Adhesive or equivalent to new gasket, and seal gasket to rocker arm cover (B). Be sure to follow the manufacturer’s directions on the package for correct application procedures and curing times. Install cover and tighten cap screws to 8 Nm (6 lb-ft) (72 lb-in.). Install fuel injection nozzles (E), leak-off lines (D) and fuel injection lines (C). Connect ventilator outlet hose to adapter on rocker arm cover and tighten clamp securely. Install water manifold.

A—Water Manifold, B—Rocker Arm Cover, C—Fuel Injection Lines, D—Leak-off Lines, E—Fuel Injection Nozzles

Complete final assembly on exhaust manifold side - Install front exhaust manifold using new gaskets. Do not tighten cap screws until sealing ring and rear exhaust manifold is installed. Install rear exhaust manifold using new gaskets and sealing ring. Tighten cap screws in sequence shown in bottom illustration to 47 Nm (35 lb-ft). Install turbocharger oil return pipe, using a new O-ring.

On some John Deere Engines, using new gaskets install intake manifold (A). Tighten cap screws to 47 Nm (35 lb ft). On some Engines, install intake coupling (B). Do not tighten clamps. On some Engines, install turbocharger (C), adapter (D), and exhaust elbow (E). Position intake adapter with turbocharger and intake manifold and tighten clamps securely.

A—Intake Manifold, B—Intake Coupling, C—Turbocharger, D—Turbocharger Adapter, E—Exhaust Elbow

On JD diesel, use new gaskets (A) and install intake manifold (B). Tighten cap screws to 47 Nm (35 lb-ft).

On JD Engines, using new gaskets and O-rings, install aftercooler and cover - Install water inlet (A) and water outlet (C) hoses. Tighten hose clamps securely. Install aneroid line (B), if equipped, and tighten securely. Install turbocharger (D) with couplings. Tighten cap screws to 47 Nm (35 lb-ft). If engine oil was drained from crankcase, install new oil filter and fill with clean oil of correct grade and viscosity. Fill cooling system with clean coolant. Perform engine break-in.

A—Water Inlet Hose, B—Aneroid Line, C—Water Outlet Tube and Hose, D—Turbocharger

Perform engine break-in - Run John Deere 6068 diesel engine at slow idle no load for 2 minutes. Check for liquid leaks. Increase RPM to fast idle, then load down to 50 rpm above rated speed for 20 minutes. Dynamometer is the preferred load control, but engine can be loaded by matching drag loads to gear selection. Recheck valve clearance and adjust as necessary. Install rocker arm cover gasket and cover. Tighten rocker arm cover cap screws to 8 Nm (6 lb-ft) (72 lb-in.). Retorque of cylinder head cap screws after engine break-in is not required.