2. If it is not the first item, check whether the clearance between the piston ring and the cylinder liner is normal while uncovering the cylinder head. If the gap is too large, it needs to be overhauled: boring cylinder, grinding shaft, replacing four sets and replacing valves. Then, while checking the piston ring clearance, check whether there is any wear deviation between the cylinder liner and the piston. If there is wear deviation, pay attention to the need to correct the connecting rod during overhaul, otherwise the engine oil will burn after a period of overhaul.