C3.4B Engines for Caterpillar Built Machines Caterpillar

Illustration 1	g03692044
Cylinder and valve location (A) Exhaust valves (B) Inlet valves

Too much valve lash can cause some broken valve stems, springs, and spring retainers. Damage to the valve mechanism will produce emissions in excess of the correct specification.

The hydraulic lifter will compensate for all normal wear of the components of the valve train.

Too much valve lash can be an indication of the following problems:

• Worn camshaft and valve lifters

• Worn rocker arms

• Bent pushrods

• Broken socket on the upper end of a pushrod

• Loose adjustment screw for the valve lash

• Issues with the hydraulic lash adjusters

If the camshaft and valve lifters show rapid wear, look for fuel in the lubrication oil or dirty lubrication oil as a possible cause.

Valve Lash Check

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Accidental engine starting can cause injury or death to personnel. To prevent accidental engine starting, turn the ignition switch to the OFF position and place a do not operate tag at the ignition switch location.

1. Find top center position for number one piston. Refer to Systems Operation, Testing and Adjusting, "Finding Top Center Position for No. 1 Piston" for the correct procedure.

2. Check the rocker arms for an engine valve lash. There should be no engine valve lash.
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   Illustration 2	g03698915
   Typical example

3. If there is an engine valve lash at any position the engine valve lash may be caused by a normal leakdown of the hydraulic lash adjuster. Push the affected rocker arm (1) against the pushrod. The rocker arm (1) should rotate as the pushrod is pushed up by the recovery of the hydraulic lifter. Once all motion has ceased test again for an engine valve lash. There should be no engine valve lash.

4. Use Tooling (A) to rotate the crankshaft in a clockwise direction. The crankshaft should be rotated 360 degrees.

5. Check the rocker arms for an engine valve lash. There should be no engine valve lash.

6. If there is an engine valve lash at any position the engine valve lash may be caused by a normal leakdown of the hydraulic lash adjuster. Push the affected rocker arm (1) against the pushrod. Monitor the rocker arm (1) for movement. The rocker arm (1) should rotate as the pushrod is pushed up by the recovery of the hydraulic lash adjuster. Once all motion has ceased test again for an engine valve lash. There should be no engine valve lash.

7. If an engine valve lash is found in any position, examine the valve mechanism components for excessive wear or damage. Examine the hydraulic lash adjusters for damage.