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 (183)

    • Guest - shelly

      My car is tappin and hittn sound. What do i do

    • Guest - Currie West

      If I buy a oil pump switch or a oil pump for a 1997 gov saffari mini van 4.3 will that stop a bottom end knock on the motor

    • Guest - cynthia

      I just rebuilt my Durango engine and I started it up and it rattles what could this possibly mean?

    • Guest - Bill

      i have a 2003 vw gti 24v vr6 golf and when it reaches higher temps it starts having a knock to it what could the problem be ?

    • I never asked about noise

    • Guest - jr gonzalez

      I got 2005 chevy silverado 5.3 sometimes it knocks while driving i stop shut it off turn the truck off and the knocking goes away its starting to do it more often what could it be?

    • Guest - sam brittendall

      can you put new rod bearings in a 2001 monte carol 3.8 engine with out pulling the engine

    • Guest - Mary H

      my son ran into a road covered in water. The car immediately died. The next morning the car cranked but now has a knocking sound. the oil is clean and there is no water in the engine. will someone please help. I am a single mom and my son uses his car for part time wok and school.

    • Guest - markiss

      In reply to: Guest - Mary H

      He dry locked the motor... Its done....

    • Guest - Vic's

      In reply to: Guest - Mary H

      Did figure out what happened

    • Guest - Vic's

      In reply to: Guest - Mary H

      That just happened to me. I ran through a puddle of water the car died and when I started it again there was a ticking noise

    • Guest - Joel

      2001 regal making a loud clicking noise when driving eventually the noise happen when I started it for 2 days then try to start it it didn't start. Mechanic said it was flywheel n torque convertor said how did I tear it up like that the flywheel well he fixed it and 4,days later it made a loud noise when started cut if off didn't start again. Took it back said I broke the bolts off into the crankshaft then call back and said transmission. The car wouldn't start how he know its the trans and my trans wasn't slipping or anything like that. 3 months before that he put an engine in my car and I drove it a month with that loud noise he probably didn't torque the bolts good when he replaced the engine the engine sounds quite.

    • Guest - darrell

      got stuck in 98 tahoe now it sounds like chain rattling on front drivers side dont know if its transfer case

    • Guest - darrell

      my 98 tahoe makeing chain rattling sound from front drivers side was stuck in mud and snow prior to the noise

    • Guest - john rogers

      My motor is make a loud nock noise y

    • Guest - James

      I have a tick in the engine of my 2006 5.3 chevy silverado that comes every now in then. I can shut it off for a while and it will ho away. Any ideas?

    • Guest - shortys transmission and auto repair shop

      In reply to: Guest - James

      Replace the oil filter and oil some filters have a spring loaded check ball that sticks if all good iv changed a lot of oil pumps and pick up tube best thing to do is take oil sensor out and install a oil pressure gauge check for low oil pressure at the time the motor is making the ticking noise.

    • 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 - frank

      In reply to: Guest - Joe

      My inpala suck

    • 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.

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