一台小四轮拖拉机大修不几天,便出现难起动、冒黑烟的现象.在厂内返修中,经检查供油角度正确,后检查气门间隙,发现进排气门间隙都发生变化.主要原因是新换的摇臂被磨损下陷很多,使气门间隙变大,进一步检查发现进排气门与摇臂处缺乏机油润滑痕迹,从而判断该故障是由于缺乏机油润滑、冷却,造成磨损加剧,气门间隙变化而难予起动. A small four-wheel tractor overhaul a few days, there will be difficult to start, black smoke phenomenon.In the factory repair, the inspection of the oil supply point of view, after checking the valve clearance and found that the intake and exhaust valve clearance have changed. The main reason is that the new rocker arm was worn and sagged so much that the valve clearance became larger. Further inspection revealed that there was a lack of lubricating oil traces on the intake and exhaust valves and the rocker arm, thus judging the failure was due to the lack of oil lubrication and cooling, resulting in increased wear , Valve clearance changes difficult to start.