WHAT IS ENGINE NOISE?
Generally, the engine operations always generate noise in the form of sound, but when the sound changes to start generating unusual and unpleasant sounds, engineers may refer to it as an unusual engine sound called Noise. It is the background or loud blowing sound different from that of the main engine or its previous stable operational sounds.
Unusual noise often develops in engines after using them for a long time, in some cases, it may develop after a short time of heavy loading. The conditions that can cause unusual sounds in engines are enormous but in most cases, the noisy sound may be an indication of fault or developing a fault.
According to car engine experts “the malfunction in the engine will reveal itself first as an unusual noise” if it is occurring in a vehicle, the problem may emerge to affect the drivability of the vehicle.
BASIC CAUSES OF ENGINE NOISE
Minor deviations from the engine’s initial arrangements such as the loosed pistons, badly worn rings or ring lands, loose piston pins, worm main bearings, and connecting rod bearings, loose vibration damper or flywheel, and worn or lost valve train components, etc. can cause unusual sound in any engine.
The combination of one or two of the above deviations can make the sound turn into noise which may lead to other problems in the engine if the signs are ignored.
Interpreting or determining the major cause of a noise in an engine cannot be done using a guessing method rather it involves the use of a highly technical method and will require the service of a specialist in the engine diagnosis.
However, where there is no availability of a specialist, I will drop little idea on how to go about an emergency situation.
HOW TO DIAGNOSE ENGINE NOISE
Tracing the source of engine noise can be very frustrating because it may be time-consuming, and may result in other technical issues, therefore it is always advisable to leave it to the expert except you have good knowledge of the engine dismantling and coupling and that the noise has the possibility of causing serious damage to the engine parts based on your physical observations.
To proceed, make a noise analysis to be able to remain focused on tracing the source from part to part. To make the analyses and start your diagnoses, use the STETHOSCOPE (a sound listening device) to listen to the engine as it runs.
The device will help to amplify the sounds coming from the engine which is a starting point to trace the possible part of the engine from which the noise is coming. The device can also help to distinguish between normal and abnormal noise.
HOW TO USE A STETHOSCOPE
Place the sound input side into various parts of the engine as it is running to identify the side where the intensity of the noise is high and mark the side and use other criteria to determine the part on that side that could generate such noise.
In other words, use the metal prod to trace the sound until it reaches its maximum intensity at that point a better evaluation can be made in regard to the source of the noise.
Another method is to use any electronic sound listening device which can help you to tune the actual sound into the device, thereby canceling other sounds from the engine and helping to trace the side with the maximum intensity quickly.
THE EIGHT (8) TYPES OF ENGINE NOISE
The entire sound of an engine is a product of the various noises coming from the actions of the moving parts but the unusual sound which is termed a noise means a deviation from the already existing sound.
Any engine can develop noise and the following parts of the engine are known to be the frequent source of engine noises:
PISTON RING ENGINE NOISE
The unusual sound of the piston ring can be heard during acceleration as a high-pitched rattling or clicking into the upper part of the cylinder. It can be caused by worn rings or cylinders, broken piston ring lands, or insufficient ring tension against the cylinder walls. The problem of the piston ring noise can be solved by simply replacing the rings, pistons, or sleeves or re-boring the cylinders.
PISTON SLAP ENGINE NOISE
The noise is usually heard when the engine is cold and often gets louder when the vehicle accelerates. It occurs when the piston slaps against the cylinder wall, resulting in a hollow, bell-like sound. The cause of the slap may be a result of worn pistons or cylinders, misaligned connecting rods, collapsed piston skirts, excessive piston-to-cylinder wall clearance, or lack of lubrication which may lead to worn bearings.
To solve the issue of piston slap, the following may be required; replacing the pistons, re-boring the cylinder, replacing or re-aligning the rods, replacing the bearings, and removing the spark plug of the affected cylinder.
PISTON PIN KNOCK ENGINE NOISE
The noise is a sharp, metallic rap that can sound more like a rattle if all the pins are loose. It originates in the upper portion of the engine and is most noticeable when the engine is idling and it’s hot. It sounds like a double knock at speeds.
The causes of such noise are; worn piston pin, piston pin boss, piston pin bushing, or lack of lubrication, resulting in worn bearings. The problem can be solved by either installing oversized pins or replacing the boss or bushings or replacing the piston.
RIDGE ENGINE NOISE
It is a very common and distinct noise as it occurs as the piston ring strikes the ridge at the top of the cylinder, the result is a high-pitched rapping or clicking noise that becomes louder during deceleration.
Though many factors can contribute to this, one known factor is when new rings are installed without removing the old ridge, the new rings will contact the ridge and make a noise.
Another factor is when the piston pin is very loose or the connecting rod has a loose or burn-out bearing, the piston will go higher and strike the ridge at the top of the cylinder making a high-pitched rapping or clicking sound.
To correct the ridge noise, remove the old ring ridge and replace the piston pin or piston.
ROD-BEARING ENGINE NOISE
This is a noise arising as a result of worn or loose connecting rod bearings, this noise is heard at idle as well as at speeds over 35 mph depending on how badly the bearings are worn, the noise can be from a light tap to a heavy knock or pound.
Shorting out the spark plug of the affected cylinder can lessen the noise unless the bearing is extremely worn. The noise is usually caused by a worn bearing or crankpin, a misaligned rod, or lack of lubrication, resulting in worn bearings.
The problem can be solved by servicing or replacing the crankshaft, and realigning or replacing the connecting rods and bearings.
MAIN OR THRUST BEARING ENGINE NOISE
It is a noise from the loosed crankshaft main bearing which produces a dull, steady knock, while the loose crankshaft thrust bearing produces a heavy thump at irregular intervals. The thrust-bearing noise might only be audible on very hard acceleration. Both of these bearing noises are usually caused by worn bearings or crankshaft journals. To correct the problem, replace the bearings or crankshaft.
TAPPET ENGINE NOISE
It is a light, regular clicking sound that is more noticeable when the engine is idling. It is caused by excessive clearance in the valve train. Another cause may be improper valve adjustment, worn or damaged parts, dirty hydraulic lifters, or lack of lubrication. The problem can be solved by adjusting the valves, replacing any worn or damaged parts, or cleaning or replacing the lifters.
ABNORMAL COMBUSTION ENGINE NOISE
They are the pre-ignition and detonation noises caused by abnormal engine combustion.
Detonation knock or ping is a noticeable noise during acceleration mostly when the engine is under load and running at normal temperature, and its excess can harm the engine.
The frequent cause of detonation is advanced ignition timing or substantial carbon deposits that get so hot, glow and re-ignite the air/fuel mixture in the combustion chamber causing usual combustion as detonation. Another cause may be a fuel with octane that is too low.
The problem may be solved by removing carbon deposits from the combustion chambers with a rotary wire brush and using higher octane gasoline. Another possible cause can be a malfunctioning EGR valve.
The above eight (8) types of engine noise are the most-likely ones responsible for most engine noise and their detection means an easy solution for any technician. Feel free to give us your feedback through the comment section.
Philip is a graduate of Mechanical engineering and an NDT inspector with vast practical knowledge in other engineering fields, and software.
He loves to write and share information relating to engineering and technology fields, science and environmental issues, and Technical posts. His posts are based on personal ideas, researched knowledge, and discovery, from engineering, science & investment fields, etc.
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