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

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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 (164)

    • Guest - Gerardo

      I accelarated my trailblazer to much a noise out of the engine started hearing and i got a messege stop engine but i kept going until the motor shut off wen i decrease the speed

    • Guest - Kmom

      My truck makes a thudding noise but only when ur driving and push down gas to accelerate it doesn't do it idling

    • Guest - eric mallon

      I got a 1998 tahoe its making a lil ticking noise after I got unstuck on some ice

    • Guest - Joe

      In reply to: Guest - eric mallon

      If you over revved the engine when stuck on the ice, you could have damaged the engine. May be a ticking valve lifter.

    • Guest - Ti

      I just bought a 2000 Chevrolet blazer. Haven't had it for a week and noticed that the longer i drive it, i start to feel a pull. When i took it to my mechanic, he said it was the main piston heating up and causing the oil pressure to drop. Which could freeze the engine. I took it back to the dealer and they tried to say nothing was wrong with the car but they would look at it. I am not sure what to do. Should i keep it if the dealership can fix it or will it be a problem later down the road

    • Guest - Bob l.

      In reply to: Guest - Ti

      Not sure what an oil pressure problem has to do with the truck pulling. There is no such thing as a main piston. Low oil pressure could be a main bearing. Yes, this could cause the engine to lock up. I would get any oil pressure problem fixed ASAP !

    • Guest - John

      The " noise seems to be be coming from passenger side underneath the power steering pump

    • Guest - John

      2001 Ford Taurus with a loud mechanical noise that is constant when engine is idling in park , reverse , drive . Would like an opinion on what could be causing this noise please .

    • Guest - DJ

      06 Ford F 150 started ticking about a week ago. Dont hear it in idle only when giving it gas and whole truck jerks especially going up hill. any ideas?

    • Guest - ken

      My 99 f-150 is making knocking noise. I do not hear it when in idle or neutral or when giving it gas

    • Guest - Stephanie J

      I have a 2004 Pontiac Grand Prix that just started Knocking and ticking yesterday. When i started the car it made a noise like something was stuck in it and now makes the other noises. The ticking is consistent but he knocking is not. Was told it is either the rods or it could be a torque bolt. Any idea?

    • Guest - Stan

      In reply to: Guest - Stephanie J

      If the motor is knocking and ticking, you have big problems. Check your oil level and see if it is contaminated with coolant. It really does not matter exactly what is making the noise, the engine has to come apart and get repaired.

    • Guest - isaac

      My 04 i35 just got out of the shop . they changed the rod bearings but its been 2 weeks and its still knocking and it started shaking? Any ideas

    • Guest - jennifer

      i just bought a 01 v6 mustang not even 5 days ago. everything was going sooooo smooth.. then when i came up on a highway toll, the car seemed to die. I put it in park and re started it.. then all of a sudden a knock/ tick started.. it is semi loud but due to my loud exhaust its kinda hard to hear.. if i go 50 mph + it seems to go away. well as i was trying to drive it to get looked at i had to wait for a train.. It died randomly again.. when i turned it back on it seemed to knock/tick more. some people keep saying it the 02 sensor, some say its the lifters that are bad.. any ideas?

    • Guest -

      Right inside cam shaft...or were I insert oil there is a ticking sound on idle...tick..tick...tick. What could it be?

    • Guest - Bob

      In reply to: Guest -

      This i a tick noise from the upper engine. Possibly a rocker arm or push rod.

    • Guest - Jarrett

      I have a 91 s10. The vehicle idles fine when in park. When I go to put it in gear it idles rough until you touch the accelerator to start moving. It does this every time I stop even at normal operating temperature. When the vehicle idles rough it will also loose oil pressure and will bottom out and almost shut off. The check oil level light will come on but the check engine light has never came on. The oil level in vehicle is fine. Just changed about 200 miles ago. The mileage is around 250xxx. What is causing this?

    • Guest -

      i have a 2006 grand prix i put to much oil in my var drove it about 10 miles then drain it out 3daya later it started knockin no smoke tho what is the knockin noise and how do i fix it

    • Guest - Tom

      I have a 98 Chevy z71 with 5.7 ltr when I accelerate real fast or go up a hill on interstate pops through throttle body and exhaust any ideas. Ty

    • Guest - Hank

      In reply to: Guest - Tom

      A pop noise is usually an engine backfire or misfire caused by an ignition problem. It could also be a bad camshaft.

    • Guest - joshua

      i got a ticking noise coming from behind my motor and transmission it a 94 s10 5speed i replaced spark plugs and so much more to much to list but its kinda funny i think its a flywheel tick cuz it only happens when i step on the gas fast if i just slowly push it down it dont make a sound and at low rpms it makes the ticking sound and then when i drive down the road it only makes the sound when i step on it hard if i take off like a 90 year old make it dont make the sound let me know what u guys think thanks!!!

    • Guest - rick wilks

      I just bought a chevy ss trailblazer 2008 and it started to smell like gas was coming in from the vents in the chevy and it was sputtering and almost stalled last night. I took it to the dealer today and told them to check it out, they called me a couple hours later and said it didn't smell of gas and no sputtering. I went up and picked it up and when I left all the lights were coming on and said it was overheating and there was 2 engine lights on and then when I turned around and basically crawled in, there was a huge puddle of milk shake lookink liquid pouring out and where you fill it up with oil was smoking. and now I am smoking from being so pissed off. Of course no mechanics were there so I have to back tomorrow am. Any comment or explanation would be great. Thank you for your time

    • Guest - Jonathan Jones

      I just came back from a trip out of town and I started hearing a knocking sound in my engine. I pulled over and put some more oil into my vehicle. The knocking became less but was still there. Once I made it home I parked it and I have not driven it since. I have however cranked it and the light knocking noise is still there. Can anyway help me better understand this. I am going to take it to a professional tomorrow. But my main question is whether the knocking noise automatically means a engine that needs replaced. Im sure it could be many things possibly causing the knock. I just wanted to know if there is a chance it could NOT be "WORSE CASE SCENARIO ENGINE BAD". Hope that makes sense. Obviously something is wrong and needs replacing or fixed. I'm just hoping there is a chance it doesn't automatically mean I have to replace my engine. Thanks for any feedback.

    • Guest - Cliff

      I got a 95 silverado 5 spd. Runs great. Has a buzzing noise in floor board like at tranny or bellhousing. And itll stop when i pull out slow then goes back and stays buzzing

    • Guest - Wolfie

      I Have A Chrysler 300 Hemi It Was Running Fine Until I Passed Alot Of Water It Was Passing The Tire And Then The Car Just Stopped I Turned It On And It Made A Really Loud Knocking Noise I Checked The Oil And It Disnt Have Any But I Had Just Changed The Oil It SmoKes Alot Out Of The Exhoust Now And The Knocking Noise Is Still Really Louds Whats Wrong Whit It ?

    • Guest - Leonie

      Hi my holden VX was driving fine no noises no sigh a of anything was wrong, I accelerated from being stopped at a roundabout and next thing u know I heard a loud clunk noise and everything went stiff like the break and steering and turned off so I tried to start it again and it was making a weird noise but not making any attempt to turn over. My partner thinks he can fix everything but dosnt always have the best outcome so I need another opinion if u can plz.

    • Guest - Jerry

      I have a 1995 chevy tahoe. Started tuning rough no check engine like and underneath the car more so by the transmission I hear a clunking noise. I have no idea what it could be any ideas?

    • Guest - kyle

      I have a 90 Chevy 1500 and there is a knocking noise and does get louder when I accelerate. Wondering what I need to do to get it fixed. I have great oil pressure and do have oil in the truck. Only has 182000 miles on it. Am I ok to keep driving it?

    • Guest - angela

      I have a 2001 Chevy venture it makes a loud ticking noise con constantly. It does it all the time.its a lot worse when I ecellerate up a hill.

    • Guest - Guest

      I have a 2001 Chevy venture it has a rel loud ticking noise especially when I ecellerateup a hill

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