Boston's Leading Mobile Mechanics

These problems may include: a badly worn piston ring or ring land; loose wrist pins; a worn main bearing or connecting rod bearing; and, loose valve train components.   All of these problems produced telltale noises that are unique.   With practice, the mechanic gains the experience and knowledge to interpret what engine noises mean, and distinguish them from one another. This can avoid costly and time-consuming engine tare down that could have been avoided.  The mechanic must take the extra time to make a proper noise analysis before doing any engine repair work. Having a heads up on the noise will reduce repair costs by addressing the problem - before any irreversible engine damage occurs.

 

Diagnosis with a Stethoscope:

Some engine sounds can be easily heard without using a listening device but others are impossible to hear and or pinpoint, unless amplified.   The tip of the metal probe of a mechanics stethoscope is used to trace the engine sound until it reaches its maximum intensity.   Once the precise location is found, the sound can be better evaluated.   A mechanic's stethoscope provides a much clearer and accurate result.   The newest tools to hit the market are electronic-listening devices.  These tools can tune into the noise and cancel out surrounding noises. This can lead to even more accurate engine noise diagnosis.

 

Some Common and Abnormal Engine Noises:

Insufficient lubrication is the most common cause of an engine noise.   A driver should always check the car’s oil level.   In this case, an engine oil-pressure test should be performed by the mechanic.  

 

One sound that is heard on an engine with high-mileage is a piston slap. This sound is heard when the engine is cold and often gets louder when the vehicle accelerates.   When a piston slaps against a cylinder wall, the sound is like a hollow dull bell type sound.   Piston slap is caused by worn pistons or cylinder walls.   In extreme situations on engines with high mileage, the car can have collapsed piston skirts and alignment issues with connecting rods.

Worn engine rings and excessive blow by can also be a sign of the problem.

 

A wrist pin knock has a unique sound. This sound is different depending on how many wrist pins are making noise.  If all the wrist pins are loose, this sounds like an overwhelming rattling inside the engine.

 

Another sound is described as a double knock, because it causes a noise at the top of the piston travel and when the piston changes direction it makes another noise.  This noise is most notable when the engine is idling and the engine is also hot.

 

An engine rod bearing noise is the most common internal engine noises. This is considered a lower- end knock.  A rod-knock is the result of a worn or loose connecting rod bearing. It is caused by poor lubrication or just wears out on high mileage engines.   This noise is heard at idle as well as higher rpms.   The severity of the noise depends on how badly the bearings are worn.   The noise ranges from a light tap to a heavy knock or even a pounding, when the bearing becomes extremely damaged or spun.   When the noise is at this level, removing the engines oil pan may expose the problem.

 

The lifter noise is one of the most common complaints.  However, the lifter noise is sometimes considered normal by several manufacturers, such as General Motors. The engine lifter noise is characterized by a light regular clicking sound that is more noticeable when the engine is idling.   It is a result of the excessive clearance in the valve train.   A clearance problem is located by inserting a feeler gauge between each lifter and valve tip.  This will differ depending on cam design. Engine lifter noise is caused by improper valve adjustment, worn or damaged parts, hydraulic lifters clogged with sludge or lack of oil pressure.

 

How to Diagnose Common Engine Noises:

a. If you hear and feel a strong, dull rotational knock, especially when the engine is pulling and the knock occurs regularly at every other rotation, this may be caused by a loose main bearing.

 

b. If you hear an irregular clicking sound, fast idle the engine, then shut off the ignition.   If you hear and feel a thud, you may have a loose fly wheel.

 

c. If you hear a tiny knock that’s most noticeable upon deceleration but can also be heard with the engine idling, your engine may have loose rod bearings.

 

d. If you hear a clicking noise with a double knock that is loudest during idling, the causes can include a loose piston pin or inadequate oil.   Clicking noises can also result from too much tappet clearance in a valve, or a hydraulic tappet is not working correctly. Clicking or tapping noises may also indicate a malfunctioning hydraulic lifter.

 

e. If you hear a ticking noise, this may indicate a problem with the fuel pump.  To diagnose, remove the fuel pump and put a plate over the hole. Run the engine with the fuel that’s left in the carburetor.  If the noise stops, it was likely caused by the fuel pump.

 

f. If you hear a ping or chatter, mostly during acceleration or when the engine is under load, this may indicate a spark plug problem.

 

g. If you hear a sharp rap at idle or higher speeds, this may indicate excessive crankshaft end play. The sound should disappear when the clutch is disengaged.