GASKET-VALVE COVER 9N3912 - Caterpillar

Probable Causes
Alternator drive belt
Alternator mounting bracket
Automatic tensioner
Alternator drive pulley
Alternator bearingsRecommended Actions
Alternator Drive Belt
Inspect the condition of the alternator drive belt. If the alternator drive belt is worn or damaged, check that the drive belt for the alternator and the pulley are correctly aligned. If the alignment is correct, replace the drive belt. Refer to Disassembly and Assembly, "Alternator Belt - Remove and Install".Alternator Mounting Bracket
Inspect the alternator mounting bracket for cracks and wear. If necessary, repair the mounting bracket or replace the mounting bracket. Ensure that the alternator drive belt and the alternator drive pulley are in alignment.Automatic Tensioner
Check the tension on the alternator drive belts. If necessary, replace the automatic tensioner. Refer to Disassembly and Assembly, "Alternator - Remove" and Disassembly and Assembly, "Alternator - Install".Alternator Drive Pulley
Remove the nut for the alternator drive pulley and then inspect the nut and the drive shaft. If no damage is found, install the nut and tighten the nut to the correct torque. Refer to Specifications, "Alternator and Regulator" for the correct torque.Alternator Bearings
Check for excessive play of the shaft in the alternator. Check for wear in the alternator bearings. The alternator is a nonserviceable item. The alternator must be replaced if the bearings are worn. Refer to Disassembly and Assembly, "Alternator - Remove" and Disassembly and Assembly , "Alternator - Install".