C15 and C18 – Engine Valve Lash – Inspect/Adjust

Note: Valve lash is measured between the rocker arm and the valve bridge. All measurements and adjustments must be made with the engine stopped and the valves fully closed.

Valve Lash Check
An adjustment is not necessary if the measurement of the valve lash is in the acceptable range in Table 1.

Table 1
Inlet Valves Exhaust Valves
Valve Lash (Stopped Engine) 0.38 ± 0.08 mm
(0.015 ± 0.003 inch)
0.81 ± 0.080 mm
(0.032 ± 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, an adjustment is necessary. Refer to “Valve Lash Adjustment” for the proper procedure.

Valve Lash Adjustment


Illustration 1 g01373511
Cylinder and valve location
(A) Exhaust valves
(B) Inlet valves

Use the following procedure to adjust the valve lash:

  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 2
    TC Compression Stroke Inlet Valves Exhaust Valves
    Valve Lash 0.38 ± 0.08 mm
    (0.015 ± 0.003 inch)
    0.81 ± 0.080 mm
    (0.032 ± 0.003 inch)
    Cylinders 1-2-4 1-3-5
  1. Adjust the valve lash according to Table 2.
    1. Lightly tap the rocker arm with a soft mallet. This action will ensure that the lifter roller seats against the base circle of the camshaft.
    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 action will put the No. 6 piston at the top center position on the compression stroke. Install the timing bolt in the flywheel.
    Table 3
    TC Exhaust Stroke Inlet Valves Exhaust Valves
    Valve Lash 0.38 ± 0.08 mm
    (0.015 ± 0.003 inch)
    0.81 ± 0.080 mm
    (0.032 ± 0.003 inch)
    Cylinders 3-5-6 2-4-6
  1. Adjust the valve lash according to Table 3.
    1. Lightly tap the rocker arm with a soft mallet. This action will ensure that the lifter roller seats against the base circle of the camshaft.
    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.

Refer to Testing and Adjusting, “Electronic Unit Injector – Adjust”.

Posted in C18

Leave a Reply

Your email address will not be published. Required fields are marked *