6.6L LB7 Duramax Diesel Engine Tick , Knock or Pop Noise - cold exhaust lifter smoke valve

When servicing the vehicle with the VIN you entered, the following diagnosis might be helpful if the vehicle exhibits the described symptoms.

Valve train induced noise. The noise may be described as a knock noise upper engine or a popping noise through the intake or exhaust.

Check the following:

1. Improper valve lash - reference SI Document number 668163.
2. Valvetrain damage due to insufficient oil flow. Verify sufficient oil to valve train. Also verify rocker arm bridge is correctly installed. Oil is splashed on the valve train components and there is no specification for the volume of oil to the valve train. However, with the valve cover off, you should see oil coating all valve train components. A blocked oil feed passage through the block or cylinder head may result in the above condition. Verify the engine has recommended oil pressure 98 kpa or 14 psi at hot idle reference SI Document number 667535 engine mechanical specification. Inspect for signs of lack of oil - components may appear rusty in color, may be dry or have a tacky oil substance coating. Insufficient oil to the valve train may lead to rocker arm damage and/or push rod tip being worn or discolored. The Duramax lubrication system supplies oil to the valve train through a passage in the block and cylinder head. Oil is then distributed through the rocker shaft to the rocker arms and push rods. For a more detailed description of the lubrication system, reference SI Document number 728023.
3. Misadjustment or rusted/sticking valve stems from lack of lubrication. If valve lash is incorrect and/or does not hold adjustment, inspect for valves sticking in the valve guides. This condition usually results in a ticking noise, but may also cause a popping/thumping noise through the intake or exhaust. Low compression may be noted on the affected cylinder(s). There may or may not be a misfire condition associated with sticking valves.

To check for sticking valves on a suspect cylinder:

•	1. Put the cylinder at top dead center of the compression stroke.

•	2. Apply shop air to the cylinder it may be necessary to prevent the crankshaft from turning by holding the crankshaft balancer bolt or installing flywheel holding tool J 44643.

•	3. Remove the valve springs using J 44646.

•	4. Remove the valve seals, as they will contribute to the feeling of a sticking condition. New valve seals should be installed upon reassembly, as the seals may be cut or distorted from removal.

•	5. With the piston still at top dead center, remove the shop air. The valves will only drop slightly before they hit the piston.

•	6. Rotate the crankshaft slightly by hand until the valves have dropped enough to allow for testing, approximately 12.7 mm (0.5 in).

•	7. Work the valves up and down in the guides while rotating them. Watch for a sticking condition.

•	8. If sticking valves are found, replace the cylinder head and the valves of the affected cylinder bank. The cylinder head is only offered as a bare casting, so valves must be ordered along with the cylinder head. Lubricate the valve stems with engine oil during reassembly.

•	To reinstall valve springs:

•	1. Rotate piston back to top dead center.

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2. Pull the valves up to their seated position and reapply shop air to the cylinder. Be sure the crankshaft does not rotate when shop air is applied or the valves may fall into the cylinder. Hold the crankshaft balancer bolt or install flywheel holding tool J 44643 to prevent crankshaft from rotating.

•	3. After lubricating valve stems with engine oil, install new valve seals using J 44640.

•	4. Install valve springs using J 44646.

•	Note: When reinstalling the rocker arm shaft assembly, be sure that the valve adjusting screws are properly seated in the pushrod cups before torquing the shaft assembly in place. A misalignment during rocker shaft installation will cause bent pushrods or a fractured pushrod cup weld.

4. Broken pushrod cup. If the valve adjusting screws were not seated properly in the pushrod cups during rocker arm shaft installation (from production or a prior service repair), the weld on the pushrod cup may be fractured when the rocker arm shaft is torqued down.

Evidence of this condition may be seen as two witness marks on the oiling hole of the valve adjusting screw where it contacted the edge of the pushrod cup during assembly. If such evidence is noted, replace the affected pushrod and inspect all other components for damage.

Please follow this diagnosis process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed. If these steps do not resolve the condition, please contact GM TAC for further diagnostic assistance. This diagnostic approach was developed for the vehicle with the VIN you entered and should not be automatically be used for other vehicles with similar symptoms.

(01, 02, 03 Chevrolet Silverado 2500 HD, 3500) and (01, 02, 03 GMC Sierra 2500 HD, 3500)