Engine Knock Sound – Explained

Engine Knock Sound – Explained


Hello, everyone and welcome in this video I’m going to be explaining engine knock. Now engine knock gets the name because it actually is an audible noise Or ping a knock or a ping that you can actually hear when it occurs in your engine So let’s talk about what’s going on. So what we’ve got going on here is kind of a sequence of events here We have a piston cylinder Engine and so this is going to be a gasoline engine and this piston is going to be on its way up in the compression Stroke, and you’re going to have an air fuel mixture in here that this spark plug is going to ignite So we’re going to start off with the spark plug igniting, and I’ve kind of gotten an overly dramatic spark there Just so you can visualize it but anyways So you have that spark ignite the pistons on its way up as that piston’s moving up and you ignite that spark you Start to have this flame front move out so this flame front moves out And it’s going to basically burn all of the air fuel mixture in that cylinder So what happens when you have knock is what’s going on is you’ve got that flame front and it’s expanding out and it’s Increasing the pressure and the rest of the cylinder as you can imagine that pressure wave basically expanding out Pressing all of this air out and increasing the pressure in here you’ve also got that cylinder moving up Which is also increasing the pressure in this area, so you’ve got a very high pressure and you’ve got an air fuel mixture in there and when you have a high pressure you’re increasing the temperature and when you increase the temperature you can have Ignition occur on its own with an air fuel mixture So what’s happening when you have knock is you know that flame front expanding and then that high-pressure high-temperature area With the Air fuel mixture will actually ignite on its own And then you have a separate flame front occurring so now you’ve got two flame fronts they’ll collide You can hear this as can be a humble thing and it can actually cause quite a bit of damage to your engine depending on the circumstances So knock is when you have a separate flame front occur after you’ve already ignited an air fuel mixture in the engine, so Once again, this is just due to the expanding pressure Increasing pressure and increasing temperature in that region due to the flame front expanding out So what are some ways that this can be prevented? Some of these are kind of design changes And then some of them’s are things that are pretty simple to do one thing you can do is a higher octane fuel So the octane rating of a fuel if you’ve watched my video on that is just simply a measure of its anti-knock Basically it’s knock resistance, so the higher octane number the more resistant to knock that fuel is Another thing you can do is retard the timing and I will have a video getting more into detail on this one And then finally kind of a design change lower compression ratio engines can run lower octane fuels They’re less likely to knock because they have lower pressures, so that’s a third thing and there’s other things that can happen But these are kind of some critical ones that can be used to change the knock characteristics of an engine So thank you for watching if you have any questions, or comments feel free to leave them below

100 Replies to “Engine Knock Sound – Explained”

  1. you explain pre-Ign. engine knock can be many different sounds, for eg. top end clatter, timing off, engine wear*

  2. Cooling the intake air also reduces the chance of knock, which is exactly why intercoolers are used.

  3. thank u sir… will u plz explain knocking in diesel engine and differnce of it with si engine?

  4. ok so my stepdad is a handyman. I have 99 vw beetle and he kept telling me there was something wrong with the transmission that he couldn't quite put his finger on. The car was driving fine for about 2 months and started making this 'CLUNK' sound when I would shift the car from P R N D. Then all of a sudden my car started overheating daily and i would have to add more antifreeze coolant every other day and the engine would still be very hot regardless of the overheating light not coming on. The Cooling fan works perfect. Basically ever since the car started shifting weird or being stuck in 1st gear the car has been overheating quickly due to the engine revving harder or going faster than it should & not on the proper gear. I really need help

  5. Hi Jason, thanks for the video. Does this apply to diesel engines too? They have no spark plug but direct injection so I am not sure whether the same wavefront phenomenon applies here. Thanks!

  6. Im pulling a lot of timing due to knock.. should I change my spark plug, coil plugs or maybe carbon build up that need to blasting like a walnut blasting?

  7. @engineering explained Hi friend, please do a video on how the engine make its noise when it's working(which we hear).I'm eagerd to know it.. your fan

  8. There are actually two types of spark knock:

    PREIGNITION – occurs when a hot piece of carbon prematurely ignites the air/fuel mixture leading to a sudden and abnormal rise in cylinder pressure and engine vibration in that cylinder
    DETONATION – primarily caused by fuel with too low an octane rating, timing too far advanced, high engine temps, or excessive carbon buildup in the cylinder

    Knock sensors are designed to detect the above, provide inputs to the computer to adjust timing — only minimizes the problem

  9. So can you help me clear one thing that whether the knocking or pinging is caused due to pre-ignition impact on the cylinder walls and piston head or due to the back pressure created by the flame front originated from the pre-ignition spot or both?

  10. So, since ignition can occur without a spark plug due to the high pressure (read, high temperature), do we have engine systems without spark plugs? If not, why not?

  11. Good job…. Made it simple.. I got some cheap gas at some crappy gas station the other day.. 2001 Dodge Ram 5.2 v8.. It knocked when accelerating.. I went to chevron and put a half tank of high octane premium and it went away.. So lesson boys and girls… Cheap gas sucks!

  12. Hi , I have a Volvo V70 and every time I start the engine if is cold I can hear for a few seconds a pretty loud knocking from the engine after that stopes .
    By the way is diesel engine .
    What can be ?

  13. My van requires only 87 octane, would it help the lifetime of the engine if I start using higher octane(91) to prevent any knocking? I appreciate all your input

  14. Only time I've ever had the misfortune of hearing pinging is from an overheating engine, pissed out all the coolant from a pipe near the throttle body, temperature sensor didn't even start budging until it was pinging for a little while already and generally running like crap. Luckily didn't do anything serious to the head or the head gasket or seize the engine. Had a nice smell of burning rubber coming from the ignition leads though lol

  15. I have a rattling noise at 1500rpm ls3 motor still don’t know what it is. Timing chain loose? Pinging? Who knows. Will take car in for tune with HD clutch & find out!!!

  16. I had my motorcycle dynoed and remapped when running super unleaded fuel. I usually still run it with 97 octane but occasionally do use 95. I haven't noticed any strange engine sounds but would welcome your opinion on this issue, particularly as the price of super has gone through the roof, here in the UK. Even normal unleaded is over £1.20 a litre now ! V-Power super is supposed to keep the valves cleaner but I don't notice any other beneficial effects, nor detrimental ones by using the cheaper stuff.
    Regards from Wales.

  17. I drive an e46 m3 with 100k miles very well maintained and I’m hearing this noise, only running on 93+ octane fuel. And a whole bunch of servicing was done to the car. Any idea how to stop this?

  18. So, for example, what about the 2012 Mazda 3's with the SkyAcive motors? The regular engine has a 10:1 compression ration and the SkyActive engine has a 12:1. Would higher octane be necessary for the SkyActive engine? Isn't that why they get better gas mileage?

  19. gpx600 I have a knock , checked cam and followers timing spot on also checked chain,,new cct, must be pre ignition?

  20. Thank God! What a relief, I'm just glad to know I can ignore the piston hanging out of the side of my engine block and the bearings and crankshaft visible through the hole in my oil pan. So I'm just getting some detonation and here I thought my engine was blown up or something

  21. Engine oil was dry and ran at high speeds of 115kmph,and suddenly on a high speed run like this sudden sound change,,as a knocking,,,,,does it cause piston to change ,,,,what is that knocking sound,is it the piston rubbing inside the cylinder?!Please do reply me

  22. My brand-new Hyundai Elantra has engine knock bad running on 87. Took it to the dealer. They said they haven't a clue what the problem is since the check engine light isn't illuminated. "Try premium" they told me. So, I filled up with 93 and the car still knocks, but to a lesser extent. Something is clearly wrong and the dealer seems to have about as much experience fixing cars as I have coding websites.

  23. What does it sound like? Driving cars for 15 years I don't think I've ever come across engine knock so I don't know what to look out for

  24. My first small engine 1,6 liter gas turbo 2008 Mini Cooper S is it normal to hear clacking like a diesel

  25. Just bought a used mini Cooper s. I'm hearing one knock on start up? Any idea what could cause this? Great video! Thanks for posting!

  26. Can someone help me understand why older engines knock? My car has 272k and just started knocking. So far high octane is taking care of it. Will it get worse?

  27. how is the title is misleading? it literally says EXPLAINED! and he explains. al lthe other knock videos on youtube just plays the audio and doesn't tell whyh it happends! thanks mate, awesome video, not misleading title, maybe people should read all the title instead of the first 3 words.

  28. Would this concept also apply to a Diesel engine? Also, could this happen if your car is just turning over and not starting?

  29. I just had my crack pully changed. but now my car has a small vibration.
    Which feels like the crank is not balanced properly.

    Its a 1.2 Ford Duratec. Can anyone help me what the problem could be?

  30. I need a good example of what it sounds like though. I want to make sure what I'm hearing is actually knock and not just the fan belt being noisy or something.

  31. I got a Cobb accessport and I use the gauge engine knock I see it goes from -1.50 to 0.00 and when I race or floor it it goes -2.50 I’m not sure how this gauge works I’m a noob at this is it bad when it goes negative?

  32. I think I'm missing something here…. I always thought that spark ignition didn't occur until just after TDC? (If the piston is still on the compression stroke then surely igniting the air/fuel mixture with the piston still travelling towards the cylinder head would cause all kinds of trouble…)

  33. I have knock issue when acceleration but my car using timing chain, Im currently using RON97 but the knocking does occur occasionally during acceleration, should I change my timing chain? Since there is no way to retard the timing due to the use of timing chain.

  34. Hey loved the video, But where could I personally message you a unique question about engine Knocking, Do you answer questions on Instagram or Facebook, where?
    I was hoping that you could help me please

    Thank You!

  35. Title misleading, I was needing an example of sounds. My condolences about you dropping out of the election race. They said you could skateboard. Well, it would be nice to hear examples to get a possible idea if air/fuel mixture is off or something is literally banking around in there. I turn the van off every time now, I want to see if it will start but the sounds are freaking me out. I like the analysis, but what does the play look like on the field? I'm more of a in the shop learner. (or broken down in the driveway in my case)

  36. I have a 2018 with Tigershark 2.4 engine. it only has 9k miles. Though a brand new car I had to take it in cause it would not start and they told me the map sensor was bad. After that I started to notice a faint knocking noise while driving (does not happen while parked) at about 2500 rpms while accelerating. I plan to take it back to the dealership, but what could this be and how much damage might this be causing? What might have caused this?

  37. 2018 wrx @29k miles. Stock tune. On freezing or below freezing cold starts i get a chatter or knocking from the engine bay area for just a few seconds
    Please help! What could cause this?

  38. Thanks for the simple explanation. My 2009 Wrangler, that I bought new, used to run fine on 87 octane fuel. Now that it is ten years old with 120000 miles, I can hear engine knock (or ping) when it is under load (going up hills) with 87 octane fuel. I started buying 93 octane fuel and the knock mostly disappeared. Had the same thing happen to my 1993 Ranger. It started knocking with low grade fuel somewhere around 120000 miles.

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