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what is the gauge pressure at the bottom of the cylinder? suppose that the density of oil is 900
The working condition of the engine depends first on the cylinder pressure of the engine. Generally, the gasoline engine is about 1000KPA, and the diesel engine is about 2000KPA. The cylinder pressure of most EFI engines is 1200~1400kPa, and the cylinder pressure of a few high compression ratio engines is above 1700kPa. The original cylinder pressure of the engine mainly depends on the volume of the combustion chamber, the compression ratio of the engine and whether there is a supercharging mechanism. In actual work, the main factors affecting the pressure of each cylinder of the engine are the amount of carbon deposited in the combustion chamber, the sealing of the combustion chamber and whether the exhaust gas is unobstructed.
Causes cylinder pressure to be too high and too low.Cylinder pressure test results may show cylinder pressures that are too high, on par, and too low. If the measured value of the cylinder pressure exceeds the standard value specified by the original factory, the cylinder pressure is too high; if the measured value of the cylinder pressure is lower than 80% to 85% of the standard value specified by the original factory, the cylinder pressure is too low. Causes of too high cylinder pressure: The main cause of high cylinder pressure is excessive carbon deposits in the combustion chamber, or excessive grinding of the joint surface between the cylinder block and the cylinder head during repairs, resulting in a reduction in the volume of the combustion chamber and a high compression ratio. Causes of low cylinder pressure: The reasons for low cylinder pressure are complex. To determine the specific cause, you can follow the steps below for an in-depth diagnosis.
Inject 20-30ml of lubricating oil into the spark plug (or fuel injector) hole of the cylinder, and then use the cylinder pressure gauge to measure the cylinder pressure again. If the re-measured cylinder pressure is significantly higher than the first time, it means that the cylinder, piston ring, and piston are excessively worn, or the piston ring is butted, stuck, broken, or pulled on the cylinder wall, resulting in the unsealing of the cylinder. If the re-measured cylinder pressure is close to the first time, it means that the intake and exhaust valves or the cylinder liner are not sealed. You can further check the following:
A. Shake the cylinder to compression top dead center, put the transmission in low gear, and tighten the parking brake.
B. Introduce high-pressure air into the cylinder from the hole of the spark plug (or fuel injector), and listen for the sound of air leakage.
C. If the exhaust pipe leaks, it means that the exhaust valve is not closed properly; if the air filter leaks, it means that the intake valve is not closed properly; if the adjacent cylinder or around the cylinder gasket leaks, the cylinder gasket is not sealed.
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