Engine Noises | Knocking and Ticking | Common Causes


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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  • Guest - Ted

    In reply to: Guest - SLM

    1999 oldsmobile alero V6 knocking noise started a while ago, noise is consistent during driving, acceleration, stopping, etc, but has gotten louder over time...?
    <br />Check for a coolant leak from the intake manifold causing the oil to look like a milkshake.

  • Guest - jharris

    my 2000 f-350 gas truck is missing when i press the gas does not do this when not pressing the gas sounds like it suppose to

  • Guest - Ted

    In reply to: Guest - jharris

    That is the sign of an ignition problem. Probably a bad spark plug or plug wire.

  • Guest - Brett

    My 1998 S10 was making a knocking sound when I would it accelerate the knocking would get louder.. The next day it got louder and I went to take of from a stop light and only got like 15 feet and then I stopped running.

  • Guest - Tony

    In reply to: Guest - Brett

    Sounds like your engine is now locked up. Either low oil pressure was what started it, or just a worn out motor.

  • Guest - trina smith

    Ihave a 2005 booneville and when I start it upto let it warm up it knocks for like 5 mins

  • Guest - duane hartley

    sounds like a valve lifter

  • Guest - Julio torres

    My brother in law has a 2004 ford expedition he recently changed the oil and spark plugs them the motor started knocking could he have done something that caused this while doing what he did.

  • Guest - Tony

    In reply to: Guest - Julio torres

    My brother in law has a 2004 ford expedition he recently changed the oil and spark plugs them the motor started knocking could he have done something that caused this while doing what he did.
    <br />Not unless a spark plug broke and part of it fell into the cylinder.

  • Guest - ernie

    i have 2003 tahoe and every morning turn the truck on it makes a knocking soud but stops in like 6 min but u can hear just a little knocking when i drive it not that loud ....is that something i should wrry about..

  • Guest - JK

    In reply to: Guest - ernie

    Yes, your engine has an internal problem. Could be an oil pressure problem, sticking valve lifters, worn bearings etc.

  • Guest - KC

    2006 Trailblazer 4.2 inline 6 has started making a tapping/clacking noise it starts about 15-20 min. after I start it then at idle it will start soft then get louder the stop then start soft and then get louder and it keeps doing this.If I take the rpm up to around 2000 then it sounds like a sharp clacking noise.When I shout off engine I can hear what seems to be something dropping in the engine???

  • Guest - KC

    Her is a link to Youtube I posted video of the engine sound.<br /><br />http://youtu.be/ABzWUrhlgT0

  • Guest - Techjk

    In reply to: Guest - KC

    If you have done any work recently, it sounds like there is something bouncing around in the cylinder. If no work done you may have a broken valve spring. If it goes away sitting at idle in gear, i would check for a broken flywheel, even if it sounds like it is coming from the top of the engine- noise travels.

  • Guest - KC

    Took valve cover off and didn't see anything that looks bad turned engine over everything looks to be ok only thing is very slight play in one of the cam gears.I'll check flywheel if not probably in the bottom of engine.I got a stethescope and the sound seems to be loudest at the bottom in the oil pan.

  • Guest - Techjk

    Bottom of oil pan means either a bad main or rod bearing or crancked flywheel.

  • Guest - Km

    I have a 2007 cobalt that has sat for over a year because I believe the motor is going on it. It is making a knocking sound when you press on the gas. This car was in a car accident as well but was still in driving condition until the knocking. I'm trying to see if it is worth me trying to fix or if I should just get what I can get for it? What would be a reasonable price to give?

  • Guest - Techjk

    In reply to: Guest - Km

    :-? That is impossible to say what the car is worth wiothout seeing it.

  • Guest - Alan

    2003 Chevy 4.3 engine manual trans. Driving to work with no problems then about of the blue started making loud noise I can't described , but If I had to say.... A bunch of hammers hitting or banging around in a dryer. So loud beyond knocking. It died at a stop light. It will start easily but shakes and runs like crap. No warning signs at all. Wasn't overheating or leaking that I could see . Possible broken valve or blown engine ? It's been a great truck want to repair it. Need to know if I need to buy a new engine, or what. Please help.

  • Guest - Tom

    In reply to: Guest - Alan

    Sounds like the engine is blown. It threw a rod or broke a piston.

  • Guest - james

    have a 98 sunfire 2.2 used liquid glass to fix head gasket changed the oil needs done again water still mixed in oil but now my valves are ticking why??? please help

  • Guest - Mike

    In reply to: Guest - james

    Don't use liquid glass !

  • Guest - Nathan Hurley

    i have a 1997 buick lesabre has a bad nock and gets worse when you accellerate the oil preasure is normal when i first start it then after it gets warm it drops slowly to no oil preasure please tell me is it the oil pump or rod bearing or what

  • Guest - Tom

    In reply to: Guest - Nathan Hurley

    Yes, sounds like worn out bearings.

  • Guest - Mike

    I have a 1998 chevy blazer 4.3 vortec i was driving then stalled started up and have heard knocking noise check egine light came on 2 days later check engine light is off driving good but still here slight knocking can it be a knocking sensor or bad gas thankyou for any help

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