what exactly is a knock???

[ONEquickGN]

I know the basics such as too much knock can and will lead to detenation and such but what is a knock? Is it an incomplete combustion from the chambers.... is it when the cylinder pressure begins blowing by the piston rings,,,, is it when the cylinder temp gets too hot or what!!??

 

[qwknuf6]

Knock!!!

Well.......I would descibe it as the the combustion charge igniting at the wrong time , self igniting due to any number of factors . When this happens the combustion presure collides with the piston as it is travleing upwards.
Kinda like taking a hammer and wacking the top of the piston downward as it moves up ,cyl. presure skyrockets as well as the cyl temp ,all bad things . This will damage head gaskets(if your lucky ) pistons ,rods , cyl. heads .nothing can hold up under severe engine knock for long , IT MUST BE AVOIDED

 

[John at J&S]

knock articles

Here are a couple good write ups:

http://www.streetrodstuff.com/Articles/September_2000/Engine_Basics_VI.php
http://www.avweb.com/articles/pelperch/pelp0043.html

 

[topfuel]

OUCH!

Knock is a nasty situation to be in if you were a turbo motor.
I believe the sound that you hear when your engine has knock,
is the sound of your pistons flexing under the severe beating
that they are taking.
NOT GOOD

 

[ONEquickGN]

thanks gwknuf6..... a perfect discription !! Not that I have any knock... just wondering exactly what it was other than the fact it was bad and the noise. Thanks guys once again!!

 

[lyonsd]

I thought knock was the sound detonation makes. Just as thunder is the sound lightning makes.

When the air-fuel mixture is ignited by the spark plug, a flame front is formed and consumes the rest of the mixture, pushing the piston down.

I thought detonation was when the air-fuel mixture begins igniting on its own, and many flame fronts are produced and collide with each other.

In other words, air-fuel ignitied by the spark plug is a controlled burn, but detonation is just an explosion.