What is the method for testing engine cylinder pressure?
2 Answers
Thread the threaded pipe fitting into the spark plug hole, or press the conical rubber fitting of the cylinder pressure gauge tightly into the spark plug hole of the cylinder being tested. Start the engine for about two seconds, read the pressure value after the pointer stabilizes, then press the one-way valve button to release pressure and reset the pointer. Note that each cylinder should be measured at least twice, with the average value being the best. The cylinder consists of the following five components: 1. Cylinder barrel: The inner diameter of the cylinder barrel determines the output force of the cylinder. The piston must slide smoothly back and forth inside the cylinder barrel. 2. End cover: The end cover is equipped with intake and exhaust ports, and some also have a buffering mechanism inside. The rod-side end cover is equipped with sealing rings and dust rings to prevent air leakage from the piston rod and external dust from entering the cylinder. 3. Piston: The piston is the pressure-bearing component in the cylinder. To prevent air leakage between the two chambers of the piston, piston sealing rings are installed. The wear-resistant rings on the piston improve the cylinder's guidance, reduce wear on the piston sealing rings, and decrease friction resistance. 4. Piston rod: This is the most important load-bearing component in the cylinder, typically made of high-carbon steel with a hard chrome-plated surface, or stainless steel, to prevent corrosion and improve the wear resistance of the sealing rings. 5. Sealing rings: The sealing of components in rotary or reciprocating motion is called dynamic sealing, while the sealing of stationary parts is called static sealing.
When I first learned car repair, my master taught me this: the engine must be completely cooled before testing. All spark plugs need to be removed, and the fuel pump fuse should be pulled to prevent fuel injection. A specialized cylinder compression gauge must be tightly connected to the spark plug hole to ensure no air leakage. Then, the throttle must be fully opened, and an assistant should crank the starter for three to four seconds to observe the highest pressure reading on the gauge. Each cylinder must be tested and recorded, with the pressure difference between cylinders not exceeding the specified range. The key to the entire process lies in proper sealing and temperature control; otherwise, the data is useless.
