What Causes the Tapping Sound When Starting the Car?
1 Answers
When the car makes a tapping sound during startup, it indicates that the hydraulic lifter is worn or the system is losing pressure. If the lubrication system has insufficient pressure or the hydraulic lifter is severely worn, the pressure inside the hydraulic lifter is insufficient to support the plunger, leading to increased valve clearance. As a result, the engine produces a tapping sound from the valves during operation. More detailed information is as follows: 1. Most engines use hydraulic lifters: The vast majority of modern car engines employ hydraulic lifters, which are components of the engine's valve train and are typically installed on the cylinder head. Their function is to open and close the valves under the drive of the camshaft while automatically adjusting the valve clearance during operation to ensure zero clearance. This helps reduce impact, lower noise, and extend the lifespan of components. 2. Reasons for the tapping sound: Under normal conditions, the hydraulic lifter is always filled with oil at a certain pressure to maintain zero valve clearance, preventing any noise from the valves during operation. However, if the lubrication system has insufficient pressure or the hydraulic lifter is severely worn, the pressure inside the lifter cannot support the plunger, causing increased valve clearance. This results in a "tapping" sound from the valves when the engine is running. Particularly in cases of severe lifter wear, when the car is parked for an extended period, the oil inside the hydraulic lifter may leak out, leading to a distinct tapping sound from the valve stems.
