How to Identify Piston Slap?
2 Answers
Methods to identify piston slap are as follows: 1. At low speed, conduct a cylinder cut-off test one by one. If the knocking sound decreases or disappears after cutting off, it indicates that the knocking comes from that cylinder. 2. At idle speed, the piston slap is obvious and clear. As the engine temperature rises or the speed exceeds medium speed, the knocking sound weakens or disappears. 3. Remove the spark plug and inject a small amount of thick lubricating oil into the cylinder from the spark plug hole. After adding the lubricating oil, use the starter to rotate the crankshaft several times to fill the gap between the piston and the cylinder wall with an oil film, then start the engine. If the knocking sound significantly weakens or disappears immediately after starting, but quickly reappears as the oil film is lost or burned, it can be confirmed that the knocking comes from that cylinder. 4. Use a long-handled screwdriver to touch the side of the engine block and listen for the sound. If the knocking is obvious and slightly vibrating, it can be confirmed that the knocking comes from that cylinder.
As an average car owner, I once heard a clicking sound from the engine during acceleration, resembling a metal rod lightly tapping the cylinder block. This knocking noise typically becomes more noticeable when RPM increases, especially when climbing slopes or during sudden throttle application. After parking, I opened the hood and used a screwdriver - placing one end against the cylinder head and the other against my ear - to precisely locate the sound source. If the noise is present during cold starts but diminishes or disappears after the engine warms up, it might indicate piston ring clearance issues. If the sound varies with throttle input, it's likely due to worn valve stems. The diagnostic method is straightforward: first check if the engine oil level is low or degraded, as poor lubrication exacerbates friction noises; then try maintaining steady speed to observe changes in the abnormal sound frequency. Remember not to ignore it - when I noticed the sound growing louder while driving, I immediately took it to a repair shop for inspection to prevent cylinder scoring and more severe engine component damage.
