Engine Noise Diagnosis Base Engine
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.
| • | There are four steps to diagnosing engine noise. They include: |
| - | The type of noise |
| - | Under which operating conditions it exists |
| - | At what rate in the engine |
| - | At what location in the engine |
| • | Compare the sounds in other engines to ensure the noise is not a normal condition. |
| • | Remember, 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. |
| • | Excessive crankshaft end play is indicated by an intermittent rap or knock sharper than a worn main bearing. |
| • | The following are causes of 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 |
| - | Loose crankshaft pulley |
| - | Loose flywheel or torque converter |
| - | 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 and is at its loudest on deceleration.
The following are causes of connecting rod bearing noise:
| • | Excessive bearing clearance |
| • | Worn crankshaft connecting rod journal |
| • | Thin, diluted, or dirty oil and/or filter |
| • | Low oil pressure |
| • | Crankshaft connecting rod journals out-of-round |
| • | Misaligned connecting rod |
| • | Connecting rod bolts not properly torqued |
| • | The wrong bearing inserts or misaligned bearing half |
Timing Gear or Chain and Sprocket Noise
Engines designed with timing gears, or those equipped with a timing chain and sprockets, can produce different 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 are causes of timing gear or chain and sprocket noise:
| • | Worn timing chain and/or gears |
| • | Misaligned gears |
| • | Excessive backlash |
| • | A damaged tooth |
| • | Gear or sprocket loose on the shaft |
| • | Too much end play in the camshaft or crankshaft |
Loose or improperly seated camshaft timing gears are usually loudest when warm. They are speed sensitive only. They are not load sensitive.
Cam gear noise will usually be evident at a warm idle in neutral and sounds much like a loose timing chain.
Piston Noise
Piston pin, piston, and connecting rod noise are hard to separate. A loose piston pin, for example, 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 its 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 are causes of piston noise:
| • | Worn or loose piston pin or bushing |
| • | 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 |
Rattle (Balance Shaft)
Balance shaft rattle sounds like a tinny, chattery rattle or a knocking noise that seems to come from the top rear of the engine. This noise is most pronounced when the engine is hot, and is not affected by engine load. An example would be dirt lodged in the root between two gear teeth. Each time the root between two balance shaft gear teeth meshes with a cam gear tooth, the balance shaft is momentarily forced upward. This pivots the shaft through the front bearing, causing a downward force on the rear bearing that eventually wears the rear bearing, causing a rattle. The following are other factors that contribute to balance shaft bearing rattle:
| • | A tight link on the timing chain |
| • | Damaged, broken, or dirty teeth on the balance shaft gears |
| • | A worn timing chain tensioner |
| • | Misaligned rear balance shaft bushing |
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. To test for a loose or cracked flywheel, operate the vehicle at approximately 32 km/h (20 mph) and 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. Check the torque converter-to-flywheel and the flywheel-to-crankshaft bolts before attempting to investigate any bearing-related knock.
Knocks Cold and Continues for 2 to 3 Minutes
Cold engine knock usually disappears when the specific cylinder secondary ignition circuit is grounded out. Cold engine piston knock which disappears in 1.5 minutes should be considered acceptable.
| • | Engine flywheel contacting the transmission converter cover -- reposition the transmission converter cover. |
| • | Loose or broken crankshaft balancer or the drive pulleys -- tighten or replace the crankshaft balancer or the drive pulleys as necessary. |
| • | Excessive piston-to-bore clearance -- replace the piston. |
| • | Bent connecting rod -- replace the connecting rod. |
Knocks at Idle Hot
| • | Inspect the drive belt for wear. Check the tension and/or replace as necessary. |
| • | Inspect the A/C compressor or generator bearing. Replace or repair as necessary. |
| • | Inspect the valve train. Replace the parts as necessary. |
| • | Inspect for improper oil viscosity. Install the proper viscosity oil for the expected temperature. Refer to Maintenance and Lubrication for the engine oil specifications. |
| • | Inspect for excessive piston pin clearance. Replace the piston and the pin as necessary. |
| • | Inspect the connecting rod alignment. Check and replace the connecting rods as necessary. |
| • | Inspect for insufficient piston-to-bore clearance. Hone the bore and fit the new piston. |
| • | Inspect the crankshaft balancer for looseness. Tighten and/or replace the worn parts. |
| • | Ensure that the piston pin is not offset to the wrong side. Properly install the piston. |
| • | Ensure that the camshaft drive gear backlash is not excessive. The knock will also be heard on a cold engine. |
Knocks on Start-Up but Only Lasts a Few Seconds
The following conditions may produce engine knocks on initial start-up, but only last a few seconds:
| • | Improper oil viscosity |
| - | Install the proper oil viscosity for the expected temperatures. |
| - | Refer to Maintenance and Lubrication. |
| • | Lifter bleed down -- clean, test, and replace the lifter as necessary. |
| - | When the engine is off, some valves will be open. Spring pressure against the lifters will tend to bleed the lifter down. Repair the lifter only if the problem is consistent. |
| - | Engines operated for only short periods between start-ups may have lifter noise that lasts for a few seconds. This is a normal condition. |
| • | Excessive crankshaft end play -- replace the crankshaft thrust bearing. |
| • | Excessive front main bearing clearance -- replace the worn parts. |
| • | Timing chain tensioner malfunction -- clean, inspect and, replace the timing chain tensioner, if required. |
Heavy Knock Hot in Heavy Load Condition
| • | Broken crankshaft balancer or pulley hub -- replace the parts as necessary. |
| • | Loose torque converter bolts -- tighten the bolts. |
| • | The drive belt is too tight or nicked -- replace the drive belt as necessary. |
| • | The exhaust system is grounded -- reposition the exhaust system components as necessary. |
| • | The flywheel is cracked -- replace the flywheel. |
| • | Excessive crankshaft main bearing clearance -- replace the crankshaft main bearings as necessary. |
| • | Excessive connecting rod bearing clearance -- replace the connecting rod bearings as necessary. |
Light Knock Hot in Light Load Condition
Light knock hot may be caused by one or more of the following conditions:
| • | Loose torque converter bolts -- tighten the torque converter bolts. |
| • | Leak at the exhaust manifold -- tighten the bolts and replace the exhaust manifold gasket if necessary. |
| • | Excessive connecting rod bearing clearance -- replace the connecting rod bearings as necessary. |
| • | Detonation or spark knock, refer to Engine Controls. |
Engine Noise Diagnosis Valve Train
| Table 1: | Momentary Noise on Engine Startup |
| Table 2: | Intermittent Noise on Idle Only |
| Table 3: | Noise at Idle |
| Table 4: | Noise at High Vehicle Speeds |
| Table 5: | Noise at Idle, Louder at High Engine Speed |
| Table 6: | Noise at any Engine Speed |
A light tapping at one-half engine speed, or any varying frequency, can 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 and use a stethoscope 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 |
| • | Broken valve rocker arm bolt |
| • | Loose or worn valve rocker arm attachments |
| • | Missing or improperly positioned lifter guides (roller lifter engines) |
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
DEFINITION: Momentary noise when the engine is started, usually cold | ||||
1 | This condition is normal. Oil drains from the valve lifters which hold the valves open when the engine is not running. The valve lifter needs a few seconds to fill with oil after you start the engine. Does the noise continue after a few seconds? | -- | Repair as required | No correction is needed |
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
DEFINITION: Intermittent noise on idle that disappears when engine speed increases | ||||
1 |
Are the valve lifters dirty or damaged? | -- | Replace the valve lifter | System OK |
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
DEFINITION: Noise at idle or with hot oil that quiets at higher engine speeds or with cold oil | ||||
1 | Inspect the lifter for a high leakdown rate. Does the lifter have a high leakdown rate? | -- | Replace the faulty lifter | No correction is needed |
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
DEFINITION: Noise at high RPM only | ||||
1 | Check for a high engine oil level. An oil level above the FULL mark allows the crankshaft counterweights to churn the oil into a foam. When the foam is pumped into the lifters, the lifters become noisy since a solid column of oil ensures the proper operation. Is the oil level too high? | -- | Drain the oil to the proper level | |
2 | Check for a low engine oil level. An oil level below the ADD mark allows the oil pump to pump air at high speeds. This causes noisy valve lifters. Is the oil level too low? | -- | Add oil as required | |
3 | Check the oil pan. Is the oil pan bent against the oil pump pickup? | -- | Repair as required | |
4 | Check the oil pump screen. Is the oil pump screen bent or loose? | -- | Repair as required | System OK |
Step | Action | Value(s) | Yes | No | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
DEFINITION: Noise at idle that gets louder as the engine speed increases, up to 1500 RPM | ||||||||||||||
1 | This noise is not connected with lifter malfunction. The noise becomes noticeable at 10 to 15 mph LOW range, or 30 to 35 mph DRIVE range. The noise is described as a ticking sound. At idle, the sound may be entirely gone or appear as a light ticking noise in one or more of the valves. This noise is caused by one or more of the following:
Are any components damaged or worn excessively? | -- | Repair as necessary | |||||||||||
2 | The noise may be an off-square valve spring. Eliminate this noise by rotating the valve spring and the valve.
Is the valve spring off-square more than 1.6 mm (1/16 in)? | -- | Replace the valve spring | System OK | ||||||||||
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
DEFINITION: Noise at all engine RPM | ||||
1 | Check for excessive valve lash. To check for valve lash, turn the engine so the piston in the cylinder is on TDC of the firing stroke. If valve lash is present, the push rod moves freely up and down with the valve rocker arm held against the valve. Is the valve lash excessive? | -- | Repair as required | |
2 | Check for a worn push rod upper end ball. Is the push rod upper end ball worn? | -- | Replace the push rod and valve rocker arm | |
3 | Check for a bent push rod. Is the push rod bent? | -- | Replace the push rod | |
4 | Check the lubrication system feed to the push rod and for a properly lubricated push rod. Are the push rod and feed system properly lubricated? | -- | Replace the push rod and valve rocker arm | |
5 | Check for a loose or damaged valve rocker arm. Is the valve rocker arm loose or damaged? | -- | Replace the valve rocker arm | |
6 | If the push rod or the valve rocker arm does not need to be replaced, this indicates trouble in the valve lifter or the camshaft. Is the camshaft worn or damaged? | -- | Replace the camshaft and valve lifters | Replace the valve lifters as necessary |
