1. Too much fuel. 2. The spray needle is jammed. 3. The valve clearance is too large (the knocking of the valves can be clearly heard). 4. The piston touches the valves. 5. The piston touches the cylinder head. 6. Valve spring is broken. 7. The lower end of the connecting rod or the bushing of the upper end of the connecting rod are worn. 8. The gap between the piston and cylinder liner is too large.
1. Adjust. 2. Adjustment or replacement. 3. Adjustment. 4. The valve seat is small, expand the valve seat. 5. Replace the head gasket with a thicker one. 6. Replace the broken spring with a new one. 7. Check and replace necessary parts. 8. Replace with a new piston or cylinder liner