One is that the cylinder head nut is not tightened or the cylinder pad is damaged by the damage of the crankshaft, such as the leakage of the cylinder head and the body, it is possible that the cylinder head nut is not tightened or the cylinder pad is damaged. In the case of the former, it should be tightened as required. For the latter, when the cylinder gasket is not seriously damaged, the asbestos line can be used to fill the damaged area and replace the new pad seriously.
Two, there are two reasons for the leakage of intake and exhaust valves. One is that the valve clearance is too small, which causes the valve to be closed tightly, and the valve clearance needs to be adjusted again. On the other hand, there may be spots on the cone of valve seal, such as rust, carbon deposition and so on. When you check, you can shake the crankshaft. If you hear the "squeaky" sound in the air filter and exhaust pipe, it means that there is air leakage in intake and exhaust valves. The valve needs to be grinded.
The three is the excessive wear of the piston ring when rotating the crankshaft, and the internal leakage of the engine body (such as oil and low shell) is mostly caused by the piston ring. Some clean oil can be added to the cylinder. If the compression force is obviously increased after joining, the piston ring should be replaced.
The opening of the piston ring to the opposite piston ring is moved to a straight line (commonly known as counterpart), or the piston ring is stuck in the ring groove due to carbon deposition, so the cylinder can not be ejected and pressed. The phenomenon is that when the crankshaft is rotated, there is a leak sound in the crankcase. The piston ring should be removed to remove the coke. If the ring is moved to a straight line, the positions of the openings should be evenly distributed, but the direction of the piston pin must be avoided.