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

Connecting rod Bearings

A damaged or worn connecting rod bearing will produce knock under all speeds. During the early stages of wear, connecting rod noise may be confused with piston slap or loose wrist 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 Chain and Gears

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 noise.

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 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.

Flywheel Noise

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 sound similar to 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.

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    Comments (151)

      Load Previous Comments
      • Paul

        In reply to: Barbara

        Does not sound like the level system. Check control arm and trailing arm bushings for being worn out.

      • leanne

        Hi. I have an 2006 Chrysler 300c, and lately it's been acting crazy. When I first turn it on in the morning, the engine knocks, the lights on the dash start flashing, gages don't read, headlights don't turn on, there's a strange sound that comes from the shifter and everything starts beeping. Also, if I attempt to turn on the wipers, they stutter. But when I restart the car, it would all away - except sometimes the lights still won't turn on. I've taken it to a mechanic who told me pep boys put the wrong oil in it, that it was too light in color and pressure was too low (19 @ rest, 39 driving). So he changed the oil, problem returned a week later. He changed it again and reset the battery. It was fine for a month, and then it came back today. What the crap?

      • Paul

        In reply to: leanne

        Engine knocking has nothing to do with the electical problems. You coud have a loose connection at the battery or alternator, a bad alternator or a loose connection at any number or wiring harnesses or grounds.

      • marc 7d2chevy

        My 1972 Chevelle has a zz3 345 hp 350 and it has a bearing sound like a water pump going out so I replaced it still doing so I tested and replaced the alternator and belt any help. Thanks.

      • duane hartley

        In reply to: marc 7d2chevy

        floting fly wheel barren worn duane hartley

      • Tom

        In reply to: marc 7d2chevy

        Remove the Belt(s) and see if the noise goes away. If it does, use a stethoscope to find out where the noise is coming from after putting the belt back on.

      • dmilford

        I have a 2006 Chevrolet Impala SS. When I get in sit on the drivers seat there is a clicking sound coming from under the passenger side dash. Some say may be the anti theft device. Some say air condition device. Any suggestions when you turn the car off it still clicks for about 10 seconds.

      • TechHeader

        In reply to: dmilford

        i have a 2006 impala SS when i get in sit on the drivers seat there is a clicking sound coming from under the pass. dash Some say may be the anti theft device some say air condition device any suggestions when you turn the car off it still clicks for about 10 sec
        <br />Anti-theft or security system will not cause a clicking in the dash. It could be a temperature door actuator motor for the A/C. If you have trouble starting it, then the noise could be caused by low voltage to a relay or computer. that can be caused by a bad ignition switch or Body Control Module (BCM).

      • bj hancock

        What if the engine is sputtering, skipping, and knocking?

      • TechHeader

        In reply to: bj hancock

        what if the engine is sputtering, skiping and nocking?
        <br />
        what if the engine is sputtering, skiping and nocking?
        <br />Sputtering and skipping is an engine misfire. Knocking is internal engine damage. This would cause the misfire. Check oil level and oil pressure. Sounds like the engine is junk.

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