我单位一台安装有F6L912型发动机的W4-60挖掘机，在使用过程中发现发动机第六缸（从发动机自由端起）气门与活塞出现顶撞的现象。调整气门间隙后，上述现象依然存在，且该缸气门间隙错乱。再次调整气门间隙，故障依旧。在进一步拆检时发现，发动机凸轮轴最后一道轴颈与机体座孔 I unit of a F6L912-equipped W4-60 excavator, found in the course of the engine sixth cylinder (from the free end of the engine) valve and the piston there is a collision phenomenon. After adjusting the valve clearance, the above phenomenon still exists, and the cylinder valve clearance disorder. Adjust the valve clearance again, the fault still. In further dismantling found that the last engine camshaft journal and body seat hole