What are the causes of engine hot piston slap?
2 Answers
The causes of engine hot piston slap are: excessive wear between the piston and cylinder leading to excessive clearance. When the piston connecting rod is twisted or the centerlines of the crankshaft main journal and connecting rod journal are not parallel, the small end of the connecting rod swings back and forth, causing the piston to swing accordingly. As the clearance increases, the swinging piston will also strike the cylinder wall, though this situation is relatively rare. When the clearance between the piston and cylinder wall is appropriate, the piston's expansion coefficient and ovality are within standard, the cylinder has no taper or out-of-roundness, the piston connecting rod is relatively vertical, and the lubrication condition of the engine oil in the hot state is good, the piston will not experience piston slap. During an overhaul, if the non-parallel crankshaft line or twisted connecting rod is not corrected, excessive wear will be aggravated when the clearance in the engine piston connecting rod section is too small. When this wear develops to a certain extent, excessive clearance will occur, and under the drive of the connecting rod, the piston will strike the cylinder wall, producing abnormal noise.
I've been driving for over twenty years and often encounter engine knocking, especially hearing metal knocking sounds after the engine warms up. It's mostly caused by incorrect ignition timing settings. If the ignition is too early or too late, uneven fuel combustion can lead to knocking. Another common reason is using low-quality gasoline with insufficient octane levels. The car requires high-grade fuel to withstand high temperatures and pressures, and using the wrong fuel can easily cause problems. Additionally, severe carbon buildup inside the engine can also be a culprit. Carbon deposits sticking to the top of the piston act like hot spots, causing the fuel to ignite prematurely and leading to knocking. Cooling system failures, such as a broken water pump or a stuck thermostat causing the water temperature to soar, can also exacerbate the issue. Worn piston rings or excessive cylinder liner gaps can cause unstable operation, directly resulting in knocking sounds. It's advisable to use high-quality gasoline, regularly clean carbon deposits, and check the ignition system. If any abnormal sounds are detected, repair them promptly to prevent cylinder damage. Also, remember to avoid constantly driving at high speeds uphill to reduce excessive load, which can help minimize occurrences.
