最近，陕西省西乡县有 2台运输型拖拉机，发动机均属 490柴油机，它们共同的故障是气门室摇臂上没有润滑油，导致摇臂处于干磨擦状态，而且在工作时发出吱吱的响声。 　　经发动机生产厂家“三保”维修人员检查：一台拖拉机的发动机是摇臂铜套外径松动，铜套错位堵住了上油孔； Recently, Xixiang County, Shaanxi Province, there are 2 transport tractors, engines are 490 diesel engines, their common fault is the valve chamber arm without lubricating oil, causing the rocker arm in a dry friction state, and squeaky at work sound. After the engine manufacturer “three guarantees” maintenance staff to check: a tractor engine rocker copper sleeve loose outer diameter, copper sleeve mismatch blocked the oil hole;