1. Piston Slap: Piston slap occurs when the pistons have excessive clearance within the cylinder walls. This can cause a knocking noise that is most noticeable at low RPMs and disappears as the engine speed increases. Piston slap is more common in older engines with high mileage or those that have not been properly maintained.
2. Wrist Pin Knock: Wrist pin knock is a similar issue to piston slap, but it involves the connecting rod's small end and wrist pin. When the clearance between these components becomes too large, it can cause a knocking noise that is often heard at idle and low RPMs.
3. Rod Knock: Rod knock is caused by excessive wear or damage to the connecting rod bearings. This can lead to a loud knocking noise that is often audible at idle and low RPMs but may diminish at higher RPMs. Rod knock is a serious issue and can lead to engine damage if not addressed promptly.
4. Main Bearing Knock: Main bearing knock is a similar issue to rod knock but involves the main bearings that support the crankshaft. Excessive wear or damage to the main bearings can cause a knocking noise that is noticeable at idle and low RPMs and may persist at higher RPMs.
5. Valve Train Noise: Various components in the valve train, such as lifters, camshafts, and rocker arms, can cause knocking or tapping noises. These noises are often more noticeable at idle and low RPMs and may diminish as the engine speed increases.
It's important to note that diagnosing engine knocks can be challenging, and it's best to consult with a professional mechanic for further inspection and diagnosis. Without proper identification and repair of the underlying cause, persistent knocking noises can lead to severe engine damage and costly repairs.
