一台东方红-12型手扶拖拉机,在检修发动机时,更换了主轴瓦、活塞环及起动轴衬套后,难以起动,同时出现严重的反转打手现象。原来以为是供油过早,但检查供油时间、活塞距上止点距离等均正常。又检查更换后的主轴瓦、连杆瓦和活塞环等相关配合件的装配情况,都没有发现问题。最后检查更换后的起动轴衬套,发现在其轴向接触面上有严重的擦 A Dongfanghong -12 walking tractor, in the maintenance of the engine, the replacement of the main bearing pads, piston rings and starting shaft bushings, difficult to start, while a serious reverse thugs phenomenon. Originally thought to be oil supply premature, but check the fuel supply time, the piston from the top dead center are normal. Also check the replacement of the main bearing, connecting rod and piston rings and other related parts of the assembly, did not find any problems. Finally check the starting shaft bushing after replacement and find that there is a serious wipe on its axial contact surface