What is Engine knocking?

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.

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