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Sounds Like Trouble: A Quick Guide to Diagnosing Common Engine Noises

 

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What do you hear when you listen to your engine? The primal roar of high performance? Or is it more like a cry for help?

OK, we never want to think of our engines doing anything but chewing up asphalt and waking up the neighbors—let alone crying! But even the manliest of mills can have problems, and the sounds they make can help us track down the troubles. Sometimes it’s nothing; sometimes it’s serious.

We’ve put together this quick guide to diagnosing common engine noises to help you avoid potential damage. In the event of strange or unusual engine sounds, remain calm, grab an automotive stethoscope, and be on the lookout for:

Valvetrain Noise

Valve and tappet noise usually begins as a clicking sound, or chatter, at half engine speed and may then disappear at high speeds. The cause is often excessive valve clearance or a defective hydraulic valve lifter.

To check your clearances, you can insert a thickness gauge between the valve stem and the rocker arm or lifter. If this reduces the noise, the cause is excessive clearance, and you’ll need to make the proper adjustments. If it does not reduce the noise, the sound may be caused by worn lifter faces or rough cams. Other things to look for include lifters that are moving loosely in their bores and weak valve springs.

Detonation

Detonation can cause serious damage to an engine. This condition shows up as a knocking or metallic “pinging” sound and is most commonly attributed to improper ignition timing, lean air/fuel ratio, or improper fuel octane level.

A somewhat common phenomenon in forced induction applications, detonation can be prevented by upping the octane level of your fuel, enriching the air/fuel mixture, reducing manifold pressure, or retarding the ignition timing. You can also consider an aftermarket water injection system for some applications.

Connecting Rod Noise

If you hear a light knocking or pounding sound, the noise can usually be traced back to your connecting rods. This sound is often most noticeable when the engine is at an even rpm–not accelerating or decelerating–and is often caused by a worn bearing or crankpin, misaligned connecting rod, or lack of oil.

You can single out the faulty connecting rod by performing a cylinder-balance test. This test basically shorts out the spark plugs one cylinder at a time with the engine running. Eventually, you’ll zero in on the ailing connecting rod because the noise will be reduced when its home cylinder is not delivering power.

 



Piston Pin Noise

Although similar to valvetrain noise, piston pin noise often has a unique, metallic-sounding double knock and is sometimes most noticeable during idle with the spark advanced. This noise is often caused by a worn or loose piston pin, worn bushing, or lack of oil.

As with connecting rod noise, you can find the offending components by performing the cylinder-balance test outlined above.

Piston Ring Noise

Piston ring noise is also similar to the valve and tappet noise above; however, it is most noticeable during acceleration. Most often, this noise is caused by low ring tension, broken or worn piston rings, or worn cylinder walls.

To troubleshoot each cylinder, remove the spark plugs and add a tablespoon of engine oil to each cylinder. Then, crank the engine for several revolutions to work the oil down past the rings. You can then install the spark plugs and start the engine. If the noise is reduced, the rings are probably the root of the problem.

Piston Slap

A hollow, muffled, almost bell-like sound is usually piston slap. This condition is caused by a piston rocking back and forth within its cylinder. Continuous piston slap means the engine needs service; however, if you only notice this sound when the engine is cold, it is likely not serious.

A continuous piston slap sound is usually caused by worn pistons, excessive piston-to-wall clearance, misaligned connecting rods, worn cylinder walls, or inadequate oil.

Crankshaft Knock

A heavy, yet dull metallic knock is typically crankshaft knock. Loudest when the engine is under load or acceleration, crankshaft knock can be diagnosed by paying close attention to the specific type of knock:

  • A regular, rumble-like knock is often from worn main bearings.
  • A more distinct knock is routinely attributed to worn rod bearings.
  • A sharp, irregular knock can be from a worn crankshaft thrust bearing.
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22 Comments

  1. Sound clips with each would be cool

  2. Bonnie J. Ladd says:

    Car engine trouble is a worry for most of us and how to diagnose these troubles is a question asked by many people. If your engine starts getting any sounds then you can determine that the engine has a commencement of a wicked problem. Likewise, each sound matches to each problem. Many of them are unaware about these sounds and they can pick up the sound, but couldn’t distinguish where the sound arrives from. Those people don’t want to worry, you always deliver the choice of getting your vehicle to any engine repair service for a diagnosing test.

  3. TApets gone on mecasion Benz help

  4. William Ottney says:

    Recently installed a built 355 with new Dart Iron Eagle heads in my 1966 Impala for HRPT15. From the get-go this engine was plagued with valve train noise. The local engine builder commented that the noise was ‘normal’. I began to suspect the noise was from excessive stem-to-guide clearance and found a couple oil-soaked sparkplugs. Cancelled HRPT15 with this ride and pulled the heads. Stem-to-guide clearance was +.005″, all 16 guides. Needless to say, I will not use this machinist/builder again. He installed new guides and now everything is quiet.
    So….excessive guide clearance can be another noise source.

  5. i have a 69 vette with a rebuilt 350 engine that only has 1000 miles on it. the other day while driving it just didn’t sound or feel right but ran and idled just fine. Sunday I went for another ride and after 20 minutes or so it seemed to be missing a bit more. all of a sudden i heard this loud clanging noise about 4 or five times and decelarated and pulled over. the sound stopped so since I was only a block from home, kept going. no more clang but does feel like it is missing/losing power. I am afraid of what it might be but starting it a couple more times in my garage, did not hear the clanging noise again but still doesn’t sound right or feels like it is missing. thanks

  6. i have a 69 vette with a rebuilt 350 engine that only has 1000 miles on it. the other day while driving it just didn’t sound or feel right but ran and idled just fine. Sunday I went for another ride and after 20 minutes or so it seemed to be missing a bit more. all of a sudden i heard this loud clanging noise about 4 or five times and decelarated and pulled over. the sound stopped so since I was only a block from home, kept going. no more clang but does feel like it is missing/losing power. I am afraid of what it might be but starting it a couple more times in my garage, did not hear the clanging noise again but still doesn’t sound right or feels like it is missing. thanks

    Reply

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  8. Mark Crull says:

    What would cause a knocking sound only at deceleration?

  9. sahil sharma says:

    Well done sir.my car was making noise and we’re not predicted by our local skilled mechanics .
    Your interpretation on engine sounds, really help me out of the prob.
    Thanks sir.
    Sahil Sharma
    India

  10. I’m running my 327 rebuilt (68 Camaro), headers, aluminum heads, etc. Very noisy on acceleration with what appears to be some miss firing when accelerating from initial takeoff, and, even noisier when hot.

  11. Pingback: Time to Rebuild (Part 1)? 7 Ways to Tell if Your Engine Needs a Rebuild Without a Complete Teardown - OnAllCylinders

  12. What if there’s only fine metal particles in the valve cover? I have a 3800 series 2 supercharged engine and the tapping noise is coming from the front top of the engine so I checked the oil for any signs of metal on the dipstick and there weren’t any. Took the oil filler cap off and saw some in the oil. It accelerates with the engine and it’s only when the engines warm to hot. Any suggestions?

  13. My b20b in my civic idles ok but its a little sluggish and sounds like a v8 when it idles. What could cause that?

  14. I have a small block 400 chev,just put new flat tappet comp cam and lifters in it idles sweet as but starts ticking under revs and ideas?

    • OnAllCylinders says:

      A few things come to mind right away such as proper break in, proper valve adjustment, and proper supporting parts like valve springs. Give the Summit tech line a call at 1-330-630-0240, and they’ll help you sort it all out!

  15. Roland Brooks says:

    I have a knocking noise only under load and louder the faster you go, at 30 its unnerving and 60 i expected a boom. Would that be main bearings? I want to be sure before i pull the engine out to swap it.

  16. Pingback: Infographic: Engine Noises and What They Could Mean - OnAllCylinders

  17. Linda Glasser says:

    Don’t know what I’m looking for a man next to me at a light said, sounds like something is wrong. Basically at idle and reverse sounds like metal rumbling. 2002 Jeep Grand Cherokee Laredo 6 cyclinder. I’m thinking maybe crank rod or pin doesn’t feel good makes me want to pull over. Your site feedback is very important. The sound discretion is very good.Grateful for the heads up. As a female its always better to have some idea of the problem before you ask for an estimate.

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