Breitling

Hey all,

I'm Bob from Ohio. I just bought a used 2007 Tahoe LT 2 days ago as a second car. This is my first Chevy! I joined the forum to learn and get tech advice... Today I noticed a chattering jackhammer-josh noise coming from the front of the engine. Any thoughts? Here's a video...

https://m.youtube.com/watch?v=WgEQT85vdtc

Thanks in advance! Glad to be here!

Vegas02ta

iTrader: (5)

Diagnosing common engine noises to help you avoid potential damage

Valvetrain Noise

Valve and tappet noise usually begins as a clicking sound, or chatter, at half engine speed and may then disappear at high speeds. The cause is often excessive valve clearance or a defective hydraulic valve lifter.

To check your clearances, you can insert a thickness gauge between the valve stem and the rocker arm or lifter. If this reduces the noise, the cause is excessive clearance, and you’ll need to make the proper adjustments. If it does not reduce the noise, the sound may be caused by worn lifter faces or rough cams. Other things to look for include lifters that are moving loosely in their bores and weak valve springs.

Detonation

Detonation can cause serious damage to an engine. This condition shows up as a knocking or metallic “pinging” sound and is most commonly attributed to improper ignition timing, lean air/fuel ratio, or improper fuel octane level.

A somewhat common phenomenon in forced induction applications, detonation can be prevented by upping the octane level of your fuel, enriching the air/fuel mixture, reducing manifold pressure, or retarding the ignition timing. You can also consider an aftermarket water injection system for some applications.

Connecting Rod Noise

If you hear a light knocking or pounding sound, the noise can usually be traced back to your connecting rods. This sound is often most noticeable when the engine is at an even rpm–not accelerating or decelerating–and is often caused by a worn bearing or crankpin, misaligned connecting rod, or lack of oil.

You can single out the faulty connecting rod by performing a cylinder-balance test. This test basically shorts out the spark plugs one cylinder at a time with the engine running. Eventually, you’ll zero in on the ailing connecting rod because the noise will be reduced when its home cylinder is not delivering power.

Piston Pin Noise

Although similar to valvetrain noise, piston pin noise often has a unique, metallic-sounding double knock and is sometimes most noticeable during idle with the spark advanced. This noise is often caused by a worn or loose piston pin, worn bushing, or lack of oil.

As with connecting rod noise, you can find the offending components by performing the cylinder-balance test outlined above.

Piston Ring Noise

Piston ring noise is also similar to the valve and tappet noise above; however, it is most noticeable during acceleration. Most often, this noise is caused by low ring tension, broken or worn piston rings, or worn cylinder walls.

To troubleshoot each cylinder, remove the spark plugs and add a tablespoon of engine oil to each cylinder. Then, crank the engine for several revolutions to work the oil down past the rings. You can then install the spark plugs and start the engine. If the noise is reduced, the rings are probably the root of the problem.

Piston Slap

A hollow, muffled, almost bell-like sound is usually piston slap. This condition is caused by a piston rocking back and forth within its cylinder. Continuous piston slap means the engine needs service; however, if you only notice this sound when the engine is cold, it is likely not serious.

A continuous piston slap sound is usually caused by worn pistons, excessive piston-to-wall clearance, misaligned connecting rods, worn cylinder walls, or inadequate oil.

Crankshaft Knock

A heavy, yet dull metallic knock is typically crankshaft knock. Loudest when the engine is under load or acceleration, crankshaft knock can be diagnosed by paying close attention to the specific type of knock:

A regular, rumble-like knock is often from worn main bearings.
A more distinct knock is routinely attributed to worn rod bearings.
A sharp, irregular knock can be from a worn crankshaft thrust bearing.

I would get a stethoscope ( looks like what the doctors use to check your heartbeat but with a modified solid tip on the end ) that way you could isolate the problem and see if its coming from your alternator , a pulley , possible valve-train . It is difficult to isolate the problem since they are so close together and yet mostly attached to each other in some way . Keep us updated