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 (158)

    • 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.

    • 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).

    • 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.

    • 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.

    • duane hartley

      In reply to: marc 7d2chevy

      floting fly wheel barren worn duane hartley

    • 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.

    • Barbara

      My 2001 Buick La Sabre has developed a double thump sound usually heard when stopping. It comes from the right rear. We have replaced the rear shocks and rear brakes so that is good. Noise seemed to stop for a while and now we notice it occasionally. How can we check to see if it is the load leveler/pump? Car appears level now but prior to the shock replacement we noticed less wheel clearance on that right rear. Steers and handles fine and brakes are great. Please advise. That occasional muffled thunk-a -thunk sound has us puzzled!

    • Paul

      In reply to: Barbara

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

    • Sally

      Thank you for this great information. I have a knocking noise in my car engine, now i think i know what the problem is.

    • jennifer

      My dodge intrepid is making a knocking sound but stops when I accelerate. The sound is most prominent when vehicle is stopped at a light or something like that. The noise decreases when vehicle is in neutral...any guesses on what it could be?? Please help!!

    • Tim

      In reply to: jennifer

      Could be a broken crank pulley or flywheel.

    • jennifer

      In reply to: Tim

      Ok I will have it checked thanks !!

    • brian

      Irecently acquired a 1998 gmc jimmy that either has a broken flywheel or rod knock. I purchased a motor but it came from a 1994 chevy s10 my question is what has to be swapped over to make the engine run without the vortech heads

    • Phil09

      In reply to: brian

      You will have to modify or change the sensors, harnesses,alternator and A/C mountings,computer, exhaust, etc.

    • Terri

      have anoise when I stop at certain spots on the road in the rear under Trailblazer

    • Samatha

      When going over bumps in the road I hear a noise in the rear under my Trailblazer what could this be ?

    • Paul

      In reply to: Samatha

      Most likly the rear stablizer bar bushings are worn our and need to be replaced.

    • duane hartley

      In reply to: Samatha

      crossmember bshings worn out

    • April

      I have a 99 chevy silveraldo 1500. When i turn on the truck and it warms up, I start driving and theres a clicking sound coming from the passenger side under the truck. It gets louder when i go from a complete stop to acceleration. Does anyone have an idea what this might be? I have people telling me that it is the flywheel, or the exhaust, or muffler, or converter... I am confused and have no idea what it is.

    • TechJ

      In reply to: April

      Could be any of those. Ticking could be a common problem of exhaust manifold bolts breaking off in the cylinder head. You should be able to hear it on one side or the other. A cracked flywheel is more noticable under the truck near the transmission.

    • crissy

      My 1998 f150 started knockin. I went right home. Next time starting it it knocked again then it just stopped. The oil pressure never dropped. What would cause a knocking noise to come and go??

    • Tech2

      In reply to: crissy

      Possibly a piece of carbon came loose from a valve and was knocking around in the cylinder. Then it got spit out.

    • jordan

      i havea 2001 grand prix and i think a rod is knocking.. it shut off on me whilei was driving one day but luckly i got it started and drove it home. It still runs but there is a very loud knocking noise do i need a new motor?

    • Tech2

      In reply to: jordan

      Ya, it sounds like it. If it was knocking bad enough to cause the car to stall, then sounds like the engine is junk.

    • Justin

      I have a 2007 torrent and there seems to be a ticking noise from the engine area if the hood is open and you have somebody give it gas the ticking does not get louder but it just speeds up with the motor . what is the problem or is that just normal ? it does not knock just ticks

    • Stosh

      In reply to: Justin

      The engine in your Pontiac Torrent does have a little ticking noise in it. If it were getting louder, then you would have a problem. If it just started, then you have a problem, if you just got the truck, i think you are hearing a normal condition.

    • Tish

      I have a 2000 mitsubushi eclipse 4 cylinder. I have recently had my belts changed do to me hearing a squealing noise when I first start up my car that morning.. It was during the winter when that happened. After it warmed up the noise would stop.. Now it is summer and I hear a knocking noise when I'm sitting in one spot.. What could be the problem?

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