Most Common Causes:
* Low Engine Oil: This is the first thing to check. Low oil pressure causes components to tap against each other. Check your oil level immediately.
* Worn or Damaged Lifters (Hydraulic Lifters): These small components regulate valve clearance. If worn or clogged with sludge, they can create a ticking or tapping sound. This is a very common cause in older engines.
* Worn Piston Rings/Pistons: If the piston rings are worn, the pistons may slap against the cylinder walls, producing a tapping sound. This is often accompanied by other issues like oil consumption and loss of power.
* Worn Connecting Rod Bearings: This is a serious issue and will typically produce a loud knock, often worsening with engine speed. It requires immediate attention to prevent catastrophic engine failure.
* Valve Train Issues (Rocker Arms, Pushrods): Worn rocker arms or pushrods can create tapping sounds.
* Timing Chain/Belt Issues: A loose or worn timing chain or (less likely in this engine) belt can cause tapping, clicking, or rattling. This one can be harder to pinpoint.
Less Common, but Possible Causes:
* Loose or Damaged Exhaust Manifold: A loose heat shield or cracked manifold can produce tapping sounds, especially when the engine is cold.
* External Component: Sometimes, the tap might not be from the engine itself. Check for loose components in the engine bay, such as brackets, shields, or accessories.
Troubleshooting Steps:
1. Check the oil level and condition: Low oil or dirty oil is a major contributor to tapping noises.
2. Listen carefully to the location of the tap: Use a mechanic's stethoscope (or even a long screwdriver pressed against your ear) to pinpoint the source. Is it near the top of the engine (valve train), the bottom (connecting rods), or somewhere else?
3. Listen to the tap at different engine speeds: Does it change with RPM? A sound that increases with RPM often indicates a problem related to engine speed, like lifters or piston slap.
4. Inspect the engine visually: Look for any obvious signs of damage or loose parts.
Important Note: Engine noises can be difficult to diagnose remotely. If you are unsure about the cause of the tapping noise, it's best to take your Buick Century to a qualified mechanic for a proper diagnosis and repair. Ignoring a tapping noise can lead to significant and costly engine damage.
