Too little valve clearance throws valves out of time. Valves open too early and close too late. This causes the valves to overheat due to hot combustion gases rushing past valves when out of time. Overheating lengthens valve stems which prevents proper seating of valves.The valves seat so briefly or poorly that normal heat transfer into the cooling system does not have time to take place,
causing burned valves and low power.
Too much valve clearance causes a lag in valve timing, causing engine valve train imbalance. The fuel-air mixture enters the cylinders late during intake stroke. The exhaust valve closes early and prevents waste gases from being completely removed from cylinders. Also, the valves close with a great deal of impact, which may crack or break the valves and scuff the camshaft and followers
This instruction show you guide on how to clear and adjust cylinder valve for John Deere PowerTech 9.0L diesel engine.
CAUTION: To prevent accidental starting of engine while performing valve adjustments, always
disconnect NEGATIVE (—) battery terminal.
IMPORTANT: Valve clearance MUST BE checked and adjusted with engine COLD.
1 Disconnect main wiring harness (B) from right side of intake manifold.
2 Remove rocker arm cover with vent tube (A).
IMPORTANT: Visually inspect contact surfaces of valve tips and rocker arm wear pads. Check all parts for excessive wear, breakage, or cracks.
Replace parts that show visible damage.Rocker arms that exhibit excessive valve clearance should be inspected more thoroughly to identify damaged parts
NOTE: Use a flexible socket extension when rotating engine to avoid interference with fuel filter assembly, as shown.
3 Remove plastic plug from cylinder block bores and install JDG820 Flywheel Turning Tool and Timing Pin
4 Rotate engine with the flywheel turning tool until timing pin engages timing hole in flywheel.
5 If the rocker arms for No. 1 (front) cylinder are loose,the engine is at No. 1 TDC-Compression.
6 If the rocker arms for No. 6 (rear) cylinder are loose,the engine is at No. 6 TDC-Compression. Rotate the engine one full revolution (360 degrees) to No. 1 TDC-Compression.
NOTE: To assist in adjusting valve clearance, push the rocker arm foot forward (A) for easier feeler gauge access (B)
IMPORTANT: If engine has been overhauled where the roller camshaft followers have been removed and/or replaced, BE CERTAIN to apply a firm downward pressure over the rocker arm adjusting screw, using push rod to seat roller follower on camshaft. Loose valve clearance settings can result if this step is not completed.
If the valve clearance is being checked or reset, this step is not necessary.
7 With engine lock-pinned at “TDC” of No. 1 piston’s compression stroke, use a bent feeler gauge to check valve clearance on Nos. 1, 3, and 5 exhaust valves and Nos. 1, 2, and 4 intake valves. If out of specification,loosen lock nut on rocker arm adjusting screw. Turn adjusting screw until feeler drag. Hold the adjusting screw from turning with screwdriver and tighten lock nut to specifications