SUPPORT AS-TRUNNION 3921782 - Caterpillar

Probable Causes
Loose rocker arm adjustment screw locknut
Insufficient lubrication
Worn rocker arm
Worn push rods
Worn valve lifters or broken valve lifters
Worn camshaft
Worn valve stem
Incorrect valve lashRecommended Repairs
Loose Rocker Arm Adjustment Screw Locknut
Check for proper installation of the rocker arm adjustment screw locknut. If the rocker arm adjustment screw locknut is loose, adjust the valve lash. Refer to Testing and Adjusting, "Air Inlet And Exhaust System".Insufficient Lubrication
Check the lubrication in the valve compartment. There must be a strong flow of oil at high engine rpm. There should only be a small flow of oil at low engine rpm. Oil passages must be clean. Pay particular attention to the oil passages that carry oil to the cylinder head. Check for sufficient lubrication between the injector tappet and the rocker arm buttons.Worn Rocker Arm
Check the rocker arms for signs of wear. If there is too much wear, install new parts or rocker arms.Worn Push Rods
Inspect the push rods for signs of wear. If there is too much wear, install new push rods. Adjust the valve lash. Refer to Testing and Adjusting, "Air Inlet And Exhaust System".Worn Valve Lifters or Broken Valve Lifters
Clean the valve train. Install new valve lifters.Worn Camshaft
Check the camshaft for wear. Adjust the valve lash. Refer to Testing and Adjusting, "Air Inlet And Exhaust System". Refer to Specifications for wear limit dimensions.Worn Valve Stem
Check the valve stems for signs of wear. Check for free movement of the valves or bent valve stems. Refer to Specifications for wear limit dimensions.Incorrect Valve Setting
Check the valve lash. Adjust the valve lash, if necessary. Refer to Testing and Adjusting, "Air Inlet And Exhaust System".