There is a possibility that the bush of the head idler gear for the camshaft is made of an inappropriate material, and therefore, it may prematurely wear and cause the gear to rattle. If this problem is left unattended, excessive stress may be exerted on the brim of the shaft, and the brim may break. If this occurs, the gear may interfere with the surrounding parts, making abnormal noise, or engine oil may leak, and at worst, interlocking between the gears could be lost, in which case the engine would stop and would not restart.