Serious abnormal noise fault of car valve
Jul 29,2025
The car is equipped with a top mounted camshaft. When disassembling, it is necessary to remove the camshaft, disconnect the engine timing chain, and first align the timing. Firstly, rotate the crankshaft until the timing mark "OT" line on the crankshaft pulley aligns with the timing indicator on the timing cover. At this point, the first cylinder is at the top dead center position of the piston, and there is a small hole with a diameter of about 4mm on the flange of the double camshaft. The lower edge of the small hole should be flush with the cylinder head, and a 3mm small hexagon can be inserted into the small hole to align the timing. Fault phenomenon: A Mercedes Benz S-Class (quoted image parameters) 300 sedan has severe abnormal noise from its valves. The valve mechanism of this car is equipped with hydraulic automatic clearance adjustment. The possibility of valve top damage or oil passage blockage is relatively high. Troubleshooting: After removing the valve cover, use a screwdriver to press down on the valve top. It was found that one of the valve tops was particularly soft, and it was determined that the valve top was damaged and caused abnormal valve noise. To identify the cause of valve top damage and troubleshoot, it is necessary to disassemble and inspect.
After disassembling the camshaft, remove the hydraulic valve top. To prevent damage to the valve top caused by blocked oil passages, blow the oil passage with compressed air to check if the oil passage leading to the damaged valve top is blocked. However, it was found that the oil passage was blocked. Open the oil passage plug in front and blow it with compressed air. Dirt was blown out from the oil passage. It turned out that the rubber of the oil filter had fallen off and entered the oil passage. After a long time, it hardened due to high temperature, blocking the oil inlet of the hydraulic valve top, causing damage to the valve top and abnormal valve noise. Upon inspection of the oil filter element, it was found that a circle of rubber on the filter element had shattered. According to the car owner's feedback, the filter element of this car has just been replaced, and it seems that the rubber of the poor quality oil filter cannot withstand high temperatures. After breaking, it enters the top oil inlet of the valve with the oil flow, causing a malfunction.
Thoroughly clean the engine oil passage and reinstall the camshaft. To prevent the piston from damaging the valve, first rotate the crankshaft to 30 ° before the top dead center of cylinder 1, then rotate the two camshafts to the correct timing position, and then turn the crankshaft to the "OT" line position. When hanging the chain, the camshaft position adjuster must be in the delayed position, that is, rotate the adjusting sprocket at the front end of the camshaft in the direction of engine crankshaft rotation until it stops moving, and then hang the chain. The camshaft position adjuster of the vehicle adjusts the valve timing to increase engine power when the engine speed is between 2500-4400r/min when the vehicle is stationary or between 2000-400Or/min while driving. When assembling the camshaft position adjuster, make sure it is in the appropriate position.
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