Mar 11, 2010

14 What is Engine Knocking? Do you really know?

Demystifying one of the most incorrectly used engine related term (in India)..

What is Engine Knocking?

If I ask this question to most of the ones who rides a motorcycle in India, I can bet that the most probable answer would be something like this:

"If you are riding at top gear and the bike is at slow speed say around 20 kmph; in such a situation if you suddenly twist the accelerator without shifting down a gear, then instead of a smooth pick up, the engine will start behaving as if it’s gasping for breadth and struggles to move forward. This causes the bike to move in a jerky manner instead of moving forward smoothly.

This is knocking

I wouldn’t be surprised if the above answer comes not just from a layman but even from many of out so called "desi" bike experts

What has been described above is actually Engine "SNATCHING" and NOT Engine "KNOCKING".

Why does Engine Snatching occur?

Imagine someone is holding your hand casually and loosely. Now if he/she decides to pull your hand suddenly then you will surely experience an unpleasant jerk won’t you? The same phenomenon occurs with the engine, when the slow moving parts inside the engine are subjected to a sudden motion.

What we instinctively do in such a situation is either shift down a gear or let the engine revs rise by slipping the clutch.

If that is Engine Snatching then what is Engine Knocking?

Engine Knocking is actually a Pinging/Metallic sound which can be heard from the engine when the air fuel mixture is not burnt in the optimum manner.

Causes of engine knocking could be: Due to..
  • Carbon deposits

  • A lean air-fuel mixture

  • Low coolant level, or cooling system problem that causes the engine to run hotter than normal

Posted below is a video in which a car engine makes "Knocking" sounds when revved: Click here, if one cannot see the video.

For more info on Engine Knocking, click here..

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This is to remind that the Views or Opinions in the blog are entirely mine unless explicitly stated. The Views and Opinions published in this blog should in no way be related to any other person or organization associated -- directly or indirectly -- with me.


Sajal said...

That's a great read Dude!! Clears a lot of concepts :)

Anonymous said...

Fantastic stuff. Simple and lucid. much better than the stuff available on other amateur auto blogs out there which are just interested in spreading sensational scoops and half cooked gyan (knowledge)

thanks again

Prakash said...

the above article clears the term 'snatching'...

however i m still not sure what 'knocking' is. wud have been better if u cud give more information on hw to identify it distinctly different than the actual engine noise??

wud b gr8 if u cud shed more light on it :)

Payeng said...

Thanks Sajal and anonymous,

@Prakash, knocking occurs due to improper detonation inside the engine.. the resulting sound is a Metallic "Pinging" noise..

I have now added a video of a car engine which makes "knocking" sounds when revved. Hope it makes the "knocking" explanation clearer now.

Goa on Wheels said...

Thanks for the info.. never heard of engine Snatching before

Anonymous said...

i want a little clarification based on engine knocking.. According to d feature 'Anti-Knocking Mechanism' in new TVS-Jive ( ),its mentioned dat one can drive in any gear at low speeds. so wen referred to knocking it means dat it is something which is related to proper speed nd correct gearshift(snatching).as mentioned above it shuld b mentioned as anti-snatching mechanism.Then y does TVS use such a kind of wrong terminology???so to what extent is engine snatching more appropriate than engine knocking?

Payeng said...

@the guy who has posted above, maybe TVS is just using the commonly used terminology so that it is easier for the average joe to understand.

Goa on Wheels said...

Thanks for the info.. never heard of engine Snatching before

Rajyavardhan Mishra said...

thnx for d informative article....i have a Qs:
which would be more fuel-economic way to handle snatching?
- applying the clutch and revving up the engine
- shifting the gears down and then up and revving up the engine
Thanks a lot.

S.P - Biker Next Door said...


According to me its always better to shift down to avoid snatching rather than making the clutch slip.

ngage25 said...

awesome explaination

utsav vyas said...

Actually term knocking is technically called detonation which is a phenomena of instateneous preignition of charge(air+fuel) rather then proper progressive combustion and this sudden ignition cause a very sharp pressure peak inside the cylinder which sounds like hammering. Parameters which responsible are compressio ratio,temp and pressure and it can be reduced by using higher octane no petrol.

utsav vyas said...

To avoid snatching , shifting to lower gear is bettre option because sliping the clutch cause more wear and tear of clutch lining and may cause overheating of clutch so we felt that engine unit is highly heated.

powerShift said...

can you please explain engine snatching in more detail?

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