Engine noise troubleshooting

Rod bearings

Regarding bearing issues, conrod bearings usually experience problems before main bearings since they are located the farthest from the main oil passage. A common symptom of this issue is a knocking sound, with the bearing that sits most distant from the oil pump being the most tending to failure. 

The knocking sound occurs when:

• The conrod bearing is worn out
• Oil clearance increase = Oil pressure decrease
• A knocking sound occurs due to metal interference in the up/down movement
• Bearing material gets spread throughout the engine

The oil pressure loss in this area results in poor oil pressure throughout the entire engine, often leading to more bearing failures. Also, excess bearing material pushed around with the oil can damage other bearings - especially if the engine rotates more after the time of the first bearing failure. 

The knocking can increase in phase if more connecting rod bearings fail.

The knocking can increase in phase if more connecting rod bearings fail.
It can be challenging to determine where the problem originated once this happens, even though the bearing furthest from the oil pump is most likely the first one to fail.

Valves

Valves can cause a ticking or knocking sound if they do not close straight down into their seats.

This is often caused by the valves hitting the pistons. However, it can also be due to debris that has gotten between the valve and the valve seat upon closure. Even a loose valve seat can create noise.

Usually, several valves in multiple cylinders are affected, and the noise quickly becomes apparent even at idle since there are many faulty valves closing and opening simultaneously.

Pistons

Pistons that make no noise when the engine reaches operating temperature. However, certain piston materials, especially when combined with a slightly larger "piston to wall clearance," can cause piston slap when the engine is cold. This noise quiets down when the engine warms up and the material expands to the desired size. (This is referred to as "piston slap" in English.)

Typically, only more extreme engines have piston slap/noise.

If noise occurs after a period of use, it is usually a problem and often stems from something other than the piston. The piston may still be the cause of the noise, but in that case, the solution is typically an engine rebuild, as pistons should not start to make noise after a period of use.

Piston pins

Noise from the bottom end can come from one or more piston pins. This is caused by excessive play due to wear or low oil pressure. The noise is more pronounced at idle and may even quiet down at certain RPMs.

The noise can be likened to valve noise, as the piston pin can often produce a double sound on a single movement—just like two or more valves do per cylinder.

Piston rings

Piston rings that create noise can be likened to valve slap, as it is not just one sound per power stroke but often multiple sounds/ticks/knocks per stroke.

This noise is caused by low tension in the piston ring, a broken or damaged piston ring, a damaged cylinder wall, or incorrect piston rings for the piston. Incorrectly installed piston rings can also cause noise.

Crankshaft

Noise from the crankshaft is not very common and can be difficult to diagnose, but some explanations for how this can occur include issues with main bearings, rod bearings, or thrust bearings.

• Main bearings produce a continuous grinding sound as they sit in the center and have more or less even loading at a given RPM.
• Rod bearings create a knocking noise due to uneven loading depending on whether the piston is moving up or down. The knock often occurs when the piston changes direction.
• Noise from thrust bearings can present itself as an irregular knock or noise. This can be diagnosed by pressing down on the clutch.

Crankcase ventilation

When a crankcase ventilation begins to become clogged, an engine can push oil out from seals/gaskets. This occurs when the engine cannot ventilate the crankcase pressure, and oil is then forced out through the seals. 

The hole in the crankcase ventilation becomes smaller and smaller, and eventually, a whistling/wailing sound may arise, similar to a wind instrument.

Check valves

The check valve exists to direct pressure and flow in a specific direction. If a check valve is broken and flow can pass both ways through the valve, a whistling or hissing sound may occur.

This sound can arise from the internal parts of the check valve that have broken and are loosely lying in the valve, resulting in an irregular pattern.

In addition to this noise, other problems can also arise as pressure/flow now passes where it should not. You can easily check a check valve by blowing into it from both directions and ensuring that one side is sealed.

Missfire

Pre-ignition occurs when an air/fuel mixture ignites before the spark from the spark plug ignites it. This is very harmful to an engine and is referred to as knocking or pinging. If pre-ignition happens regularly, the car sounds like a diesel.

If it only happens occasionally, it is harder to hear, but if you know that many sounds like a diesel, you can get an idea of how a few might sound. If this occurs during driving or under load, it is often felt as jolts.

All types of pre-ignition are very harmful to the engine and should be addressed immediately. The cause of this is excessive heat buildup due to incorrect ignition timing or a lean fuel mixture.

Turbocharger

A turbo that makes noise is often characterized by hissing or whistling sounds. First and foremost, vacuum leaks should be checked, as this is the most common cause. If everything is sealed, it is most likely the turbo itself that is making the noise.

If your turbo has started to make a lot of noise after a period of use, the turbine/compressor wheel may be damaged, resulting in a whistling noise.

If the turbo is over-revved, a whistling noise can also occur.

Vacuum leak

Vacuum leaks often sound like hissing or wheezing, especially if the engine is supercharged with a turbo or compressor. This leakage usually comes from vacuum hoses, but it can be a leak from any line or joint.

The type of leak and the truck determine the type of sound and can vary. A simple pressure test of the engine will indicate where the leak is located.

Injectors

Injectors can also make noise, typically in the form of ticking. This can often be checked more easily by feeling the injectors with your hand. If they are ticking, you can usually feel this as well. Then unplug one injector's connector and see if the noise disappears or changes.

A ticking injector is not something that can be repaired; it's simply the construction that makes that noise. As long as it functions properly, it’s fine. If you are unsure about the injector's function or condition, you can send them in for an injector inspection/service.

Cam followers

If a ticking or knocking sound comes from the top, it could be the valve lifters that are the problem. If the valve lifters are noisy, they have too much play. There are hydraulic and mechanical valve lifters, and they are handled differently.

Hydraulic Valve Lifters
If you have hydraulic valve lifters that are noisy, the oil pressure may be low. Alternatively, it could be dirt preventing oil from adjusting the lifter to the correct valve clearance. These should then be replaced with new ones. The lifter may also be worn, but often the camshaft is worn as well, and both must be replaced along with other checks.

Using the wrong type of oil can also cause problems with hydraulic lifters.

Mechanical Valve Lifters
If you have mechanical valve lifters, they should be adjusted through setting. If this does not work, they can be adjusted with shims.

Connecting rods

Noise from connecting rods is usually caused by rod bearings or excessive play between the piston pin and the connecting rod's bushing at the small end. However, noise can also originate from the connecting rod itself. The most common cause is a bent connecting rod.

This type of noise often occurs at a stable, steady RPM, meaning it does not occur when the RPM increases or decreases, and the sound can vary in character depending on the engine and type of connecting rod.