C7 Industrial Engines Testing and Adjusting – Engine Valve Lash – Inspect/Adjust

Note: Valve lash is measured between the rocker arm and the bridge for the inlet valves. Valve lash is measured between the rocker arm and the valve stem for the exhaust valve. All of the clearance measurements and the adjustments must be made with the engine stopped. The valves must be fully closed.

Valve Lash Check

An adjustment is not necessary if the measurement of the valve lash is in the acceptable range. Adjust the valve lash while the engine is stopped. The range is specified in Table 1.

Table 1
Inlet Valves Exhaust Valves
Valve Lash Check (Stopped Engine) 0.38 ± 0.08 mm (0.015 ± 0.003 inch) 0.64 ± 0.08 mm (0.025 ± 0.003 inch)
TC Compression Stroke 1-2-4 1-3-5
TC Exhaust Stroke (1) 3-5-6 2-4-6
Firing Order 1-5-3-6-2-4 (2)
( 1 ) 360° from TC compression stroke
( 2 ) The No. 1 cylinder is at the front of the engine.

If the measurement is not within this range adjustment is necessary. See Testing And Adjusting, “Valve Lash And Valve Bridge Adjustment”.

Illustration 1 g01320108
Cylinder and Valve Location

(A) Exhaust valve

(B) Inlet valves

Valve Lash and Valve Bridge Adjustment

Illustration 2 g01109236
(1) Exhaust rocker arm

(2) Inlet valve bridge

(3) Rocker arm adjustment screw locknut for the exhaust rocker arm

(4) Rocker arm adjustment screw for the exhaust rocker arm

Table 2
Valve Lash
Valves Dimension of Gauge
Inlet 0.38 ± 0.08 mm (0.015 ± 0.003 inch)
Exhaust 0.64 ± 0.08 mm (0.025 ± 0.003 inch)

Adjust the valve lash while the engine is stopped.

 

  1. Put the No. 1 piston at the top center position on the compression stroke. Refer to Testing and Adjusting, “Finding Top Center Position for No. 1 Piston”.
    Table 3
    TC Compression Stroke Inlet Valves Exhaust Valves
    Valve lash 0.38 ± 0.08 mm (0.015 ± 0.003 inch) 0.64 ± 0.08 mm (0.025 ± 0.003 inch)
    Cylinders 1-2-4 1-3-5

 

  1. Adjust the valve lash according to Table 3. 
    1. Lightly tap the rocker arm at the top of the adjustment screw with a soft mallet. This will ensure that the lifter roller seats against the camshaft’s base circle.

     

    1. Loosen the adjustment locknut.

     

    1. Place the appropriate feeler gauge between rocker arm and the valve bridge. Then, turn the adjustment screw in a clockwise direction. Slide the feeler gauge between the rocker arm and the valve bridge. Continue turning the adjustment screw until a slight drag is felt on the feeler gauge. Remove the feeler gauge.

     

    1. Tighten the adjustment locknut to a torque of 30 ± 7 N·m (22 ± 5 lb ft). Do not allow the adjustment screw to turn while you are tightening the adjustment locknut. Recheck the valve lash after tightening the adjustment locknut.

 

  1. Remove the timing bolt and turn the flywheel by 360 degrees in the direction of engine rotation. This will put the No. 6 piston at the top center position on the compression stroke. Install the timing bolt in the flywheel.
    Table 4
    TC Exhaust Stroke (3) Inlet Valves Exhaust Valves
    Valve lash 0.38 ± 0.08 mm (0.015 ± 0.003 inch) 0.64 ± 0.08 mm (0.025 ± 0.003 inch)
    Cylinders 3-5-6 2-4-6
    ( 3 ) Position for No. 1 cylinder

 

  1. Adjust the valve lash according to Table 4. 
    1. Lightly tap the rocker arm at the top of the adjustment screw with a soft mallet. This will ensure that the lifter roller seats against the camshaft’s base circle.

     

    1. Loosen the adjustment locknut.

     

    1. Place the appropriate feeler gauge between rocker arm and the valve bridge. Then, turn the adjustment screw in a clockwise direction. Slide the feeler gauge between the rocker arm and the valve bridge. Continue turning the adjustment screw until a slight drag is felt on the feeler gauge. Remove the feeler gauge.

     

    1. Tighten the adjustment locknut to a torque of 30 ± 7 N·m (22 ± 5 lb ft). Do not allow the adjustment screw to turn while you are tightening the adjustment locknut. Recheck the valve lash after tightening the adjustment locknut.

 

  1. Remove the timing bolt from the flywheel after all adjustments to the valve lash have been made. Reinstall the timing cover.
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