What is the working principle of engine valves?
3 Answers
The working principle of engine valves is driven by the camshaft through tappets and push rods. Symptoms of engine valve leakage: Valve leakage leads to weak vehicle performance, excessively rich or lean air-fuel mixture, incomplete combustion of fuel in the combustion chamber, resulting in increased fuel consumption; Valve leakage can also cause slow acceleration. Engine valve leakage can make the engine difficult to start, reduce power, cause incomplete combustion, severe carbon buildup, and even lead to individual cylinders not working. Causes of engine valve leakage: Valve burning leads to decreased sealing between the valve and valve seat; Valve clearance adjusted too small, causing the valve to not close tightly; Carbon buildup on the conical surface of the valve and valve seat; Foreign objects stuck during valve installation causing poor sealing; Pitting, scratches, spots, burns, or dents on the valve working surface; Poor grinding of valve sealing rings during maintenance; Excessive runout of the valve and valve stem; Excessive coaxiality deviation between the valve guide hole and seat hole.
During my recent car repairs, I discovered that engine valves are like the nostrils that allow the engine to breathe. When the camshaft rotates, the egg-shaped cams on it sequentially push the valves open. In a gasoline engine, for every two rotations, the intake valve opens to suck in fresh air as the piston moves down, and when the piston compresses the air on its way up, the exhaust valve expels the burnt exhaust gases. The key component is the valve spring—a metal coil that snaps the valve back into place each time the cam pushes it open. If this spring weakens or the valves get carbon buildup, the car noticeably struggles to breathe, and the engine starts coughing with a sputtering sound.
Last time I modified my old car, I finally understood that valves are essentially the gatekeepers of the engine's intake and exhaust. The crankshaft belt drives the camshaft to rotate, and those cams act like pile drivers, forcefully pushing the rocker arms to press down the valve stems and open a gap. When a gasoline engine inhales, the intake valve opens to let in the air-fuel mixture, and after combustion, the exhaust gases are expelled through the exhaust valve. Poor sealing of the valve seat is like a drafty door gap, causing the car to mysteriously lose oil on long trips. Nowadays, new cars use variable valve timing technology, akin to equipping the gatekeeper with a smartwatch—opening the door precisely when needed.
