Caterpillar engine tappit clearance or valve lash.

Valve clearance or valve lash is measured with a feeler gauge setting Gage put between the rocker arm contact and the bridge wear seat. Valve clearance is changed using a screwdriver.

A 3/4 inch wrench is needed to loosen and tighten the lock-nut which holds the adjustment screw. To make the adjustment, turn the adjustment screw until you feel an easy pull on the feeler gauge as you move it backward and forward between the rocker arm contact and the bridge wear seat. Tighten the nut on the adjustment screw and check the adjustment to be sure it has not changed. The adjustment of all valves and the injectors can be done by putting the engine crankshaft in two positions. Refer to the Service Manual for these procedures.