Engine Noise Diagnosis
Engine Noise Diagnosis (General Description)
Notice: Some engine noise is characteristic to the design. Compare the sounds in other engines in order to make sure that you are not trying to correct a normal condition.
^ Use the following four elements when diagnosing engine noise:
- The type of noise
- Under which operating conditions the noise exists
- At what rate the noise exists in the engine
- At what location the noise exists in the engine
^ Compare the sounds in other engines in order to ensure that the noise is not a normal condition.
^ Engine noise is generally synchronized to either engine speed (caused by the crankshaft, connecting rods or pistons) or one-half engine speed (valve train noise). Try to determine the rate at which the noise is occurring.
Main Bearing Noise
^ Damaged or worn main bearing noise is revealed by dull thuds or knocks which happen on every engine revolution. This noise is loudest when the engine is under heavy load.
^ An intermittent rap or knock sharper than a worn main bearing indicates excessive crankshaft end play.
^ The following conditions cause main bearing noise:
- Low oil pump pressure
- Thin, diluted, or dirty oil and/or filter
- Excessive main bearing clearance
- Excessive crankshaft end play
- Out-of-round crankshaft journals
- Excessive belt tension
- A loose crankshaft pulley
- A loose flywheel or torque converter
- A loose main bearing cap
- Belt pilling
Connecting Rod Bearing Noise
A damaged or worn connecting rod bearing will produce a knock under all speeds. During the early stages of wear, connecting rod noise may be confused with piston slap or loose piston pins. Connecting rod knock noise increases in volume with engine speed. This noise is loudest on deceleration.
The following conditions cause connecting rod bearing noise:
^ Excessive bearing clearance
^ A worn crankshaft connecting rod journal
^ Thin, diluted, or dirty oil and/or filter
^ Low oil pressure
^ Crankshaft connecting rod journals out-of-round
^ A misaligned connecting rod
^ Connecting rod nuts not properly torqued
^ The wrong bearing inserts or misaligned bearing half
Timing Chain and Sprocket Noise
Engines equipped with a timing chain and sprockets may produce noise. The most common noise is a high frequency, light-knocking sound. This sound will generally be the same in intensity whether the engine is idling, operating at high speeds, or under load.
The following conditions may cause timing chain and sprocket noise:
^ A worn timing chain
^ A damaged sprocket
^ A loose sprocket on the camshaft or crankshaft
^ Too much end play in the camshaft or crankshaft
Piston Noise
Piston pin, piston, and connecting rod noise are hard to separate. A loose piston pin causes a sharp double knock usually heard when the engine is idling, or during sudden acceleration then deceleration of the engine. A piston pin that has been improperly fitted will emit a light ticking noise that is more noticeable with no load on the engine. Excessive piston-to-cylinder bore clearance will cause a piston slap noise. The noise is similar to a metallic knock, as if the piston were slapping the cylinder wall during the stroke.
As with most engine noise, understanding the cause of the noise will help you imagine what the noise sounds like. An indication of piston slap is a decrease in noise as the engine warms up. When the engine is cold, the piston-to-bore clearance is greater and piston slap will be louder. The following conditions may cause piston noise:
^ A worn or loose piston pin
^ Improper pin fit
^ Excessive piston-to-cylinder bore clearance
^ Lack of lubrication
^ Carbon deposits on top of the piston striking the cylinder head
^ Worn or broken piston ring land
^ Broken or cracked piston
^ Misaligned connecting rods
^ Worn or damaged rings
^ Excessive ring land clearance
^ Insufficient ring-end gap clearance
^ Piston 180 degrees out of position
^ Incorrect skirt profiles
Flywheel Noise
Notice: Converter bolts that are too long may dimple the torque converter clutch apply surface and cause a shudder condition.
A loose or cracked flywheel will produce an irregular thud or click. Complete the following steps in order to test for a loose or cracked flywheel:
1. Operate the vehicle at approximately 32 km/h (20 mph).
2. Shut off the engine.
If a thud is heard, the flywheel may be loose or damaged. This type of thud is loudest on deceleration.
Loose torque converter-to-flywheel or flywheel-to-crankshaft bolts will resemble a bearing knock. This condition produces several raps during quick acceleration on a free-running engine. Depending on the idle smoothness, when the transaxle is in gear, the noise may or may not appear.
Inspect the torque converter-to-flywheel and the flywheel-to-crankshaft bolts before attempting to investigate any bearing-related knock.
Valve Train Noise
A light tapping at one-half engine speed, or any varying frequency, may indicate a valve train problem. These tapping noises increase with the engine speed. Warm up the engine before attempting to judge the valve train noise. This will bring all of the engine components to a normal state of expansion. Run the engine at various speeds and listen for engine noise with the hood closed.
Caution: The following procedure is not recommended on engines with stainless steel exhaust manifolds because manifold temperature will exceed the flash point of the oil causing a fire with possible personal injury.
If the valve mechanism is abnormally noisy, remove the valve rocker arm covers. Use a stethoscope in order to determine which valve train components are causing the noise. The causes of the valve noise include the following conditions:
^ Broken or weak valve springs
^ Sticking or warped valves
^ Bent push rods
^ Dirty, stuck, or worn valve lifters
^ Damaged or improperly machined camshaft lobes
^ Insufficient or poor oil supply to the valve train (low oil pressure)
^ Excessive valve stem-to-guide clearance
^ Worn valve guides
^ Worn push rods
^ Worn valve rocker arms
^ A broken valve rocker arm bolt
^ Loose or worn valve rocker arm attachments
^ Missing or improperly positioned lifter guides (roller lifter engines)
Engine Noise Diagnosis (Symptom - Cause/Correction)
Exhaust
Valve Train
Base Engine