Cylinder pressure refers to the size of the cylinder compression force when the piston reaches the top dead center at the end of compression. Insufficient cylinder pressure means that the sealing performance of the cylinder is reduced, which will reduce the engine power and make it difficult to start. If the individual cylinder pressure is insufficient, the engine will run unstable.

1. Cause of failure

1) The side clearance and open end clearance of the piston ring are too large, or the labyrinth route of the gas ring opening is shortened, or the sealing of the piston ring; after the surface is worn, its sealing performance becomes poor.

2) Excessive wear between the piston and the cylinder will increase the gap between the matching cylinder and the piston will swing in the cylinder, which will affect the good sealing of the piston ring and the cylinder.

3) Because the piston ring is stuck in the piston ring groove due to glue and carbon deposits, the elasticity of the ring itself cannot be exerted, and the first sealing surface between the gas ring and the cylinder wall is lost.

Cylinder strain. When the cylinder is pulled, the seal between the piston ring and the cylinder is broken, resulting in low cylinder pressure.

5) Mismatched piston is installed. For some engines, the depth of the pit on the top of the piston is different, and the wrong use will affect the cylinder pressure.

6), the cylinder head gasket is damaged, the valve seat ring is loose, the valve spring is broken or the spring is insufficient, the valve and the valve guide are not tightly sealed due to carbon deposits or the gap is too small, so that the up and down movement of the valve is blocked, etc.;-

. 7) The timing gear is installed incorrectly, the gear keyway is incorrect, the timing gear is damaged or worn too much, the wheel load on the camshaft timing gear and the wheel are loose, etc., resulting in incorrect gas distribution phase.

8) Unmatched cylinder heads are used. If there are cylinder heads, the combustion chamber volume may be different. If they are installed incorrectly, the cylinder pressure will be affected.

Improper adjustment of the clearance of the intake and exhaust valves, or: poor sealing with the valve seat, or improper operation when testing the cylinder pressure.

10) For an engine equipped with a decompression device, the clearance of the decompression device is improperly adjusted, so that the valve is not tightly closed.

2. Troubleshooting

At present, there are many methods to detect the cylinder pressure with the cylinder pressure gauge. The cylinder pressure can be detected by measuring the current of the starter and the voltage of the starter; the other two methods can also be measured cylinder by cylinder with the compressed air of the hose.

Use the cylinder pressure gauge to detect the cylinder pressure: when the engine is in a positive hot state, the coolant is at 85-95'C, and the lubricating oil temperature is at 70-90'C. At the same time, the carburetor throttle valve and choke valve are in the fully open position, the spark plugs are completely removed, the crankshaft is driven by the starter, the cylinder pressure gauge is read out and corresponding maintenance measures are taken according to the measurement results.