Most Common Causes:
* Rod knock: This is a serious issue indicating damage to the connecting rods, possibly due to low oil pressure, worn bearings, or a lack of lubrication. It's characterized by a loud, rhythmic knocking that increases with engine speed. This requires immediate attention and likely a rebuild or engine replacement.
* Main bearing knock: Similar to rod knock, but involves the bearings supporting the crankshaft. It often presents as a deeper, heavier knocking sound. Also very serious and requires professional attention.
* Piston slap: A less severe knocking, often heard when the engine is cold. It's caused by excessive clearance between the pistons and cylinder walls. It may improve as the engine warms up but should still be investigated.
* Wrist pin knock: This involves the pin connecting the piston to the connecting rod. A knocking sound will be present, potentially worsening with engine speed.
* Valvetrain issues: Worn or damaged lifters, rocker arms, or pushrods can cause a ticking or knocking sound that can vary in intensity.
* Timing chain/belt issues: A loose, worn, or damaged timing chain or belt can cause a knocking or rattling sound, especially at certain engine speeds.
* Exhaust manifold leak: While not directly an engine knock, a leak in the exhaust manifold can create a metallic knocking sound.
* Loose or damaged components: Something as simple as a loose heat shield or other component could be rattling and creating a noise mistaken for a knock.
Less Common but Possible Causes:
* Low oil pressure: This can lead to many of the above issues. Check your oil pressure gauge.
* Incorrect valve adjustment: Improperly adjusted valves can lead to noises.
* Insufficient lubrication: Using the wrong oil or neglecting oil changes can cause serious internal damage.
Diagnosing the Problem:
Pinpointing the exact cause requires a mechanic's expertise. However, you can help by providing the following information:
* When does the knocking occur? (Cold start, high RPM, specific engine load)
* Where does the sound seem to originate from? (Top, bottom, side of the engine)
* How loud is the knocking?
* Does the knocking change with engine speed?
* Have you recently had any engine work done?
* What is your oil pressure reading?
Do not continue to drive the car if you suspect a serious internal engine knock like rod or main bearing knock. Doing so risks catastrophic engine failure. Take it to a qualified mechanic immediately for diagnosis and repair.
