What are the causes of timing gear noise?

[McChase]

The causes of noise in the engine timing gear are as follows: 1. Poor lubrication leading to blockage of the main oil passage nozzle hole, improper assembly, or excessively thin diaphragm and excessively small clearance. 2. During maintenance and repair, the cam timing gear assembly is installed crookedly, causing uneven friction between the convex surface and the flange, resulting in sharp metal noise. 3. Excessive gear meshing clearance, presence of impact load, and mutual impact of tooth surfaces produce different sounds. The diagnostic methods for gear noise are as follows: 1. The noise is clearly audible on the side of the engine gearbox, unaffected by temperature and 'fuel cut-off.' The noise caused by excessive meshing clearance occurs during gear transmission. 2. The noise from tooth impact is more noticeable during acceleration. The noise caused by abnormal meshing is similar to a 'howling' sound, and its pitch changes with the speed. 3. If an individual tooth is damaged, a regular impact sound will be produced as the engine operates, and the noise is more noticeable at slightly higher idle speeds. The noise is most clearly heard when a metal rod is pressed against the timing gearbox cover.