What would cause a knock..

SxyXc · 04-15-2008, 04:00 PM

trying to help a friend.. He has a knock in his lightning.. the guy before him brought it and had some engine work done, a week after he sold him the car a knock formed. What are causes of knocks? how bad can they be? how can you fix them? Don't know anything but it had work done then a knock formed.. and he can't get a hold of the last owner... I want to know most of the common causes of knocks and how to fix them.. and about the price range..

Thanks in advance

Steven

SxyXc · 04-15-2008, 10:16 PM

please tell me if i am wrong on this one.
1) If the wrong fuel was used (not premium) the engine would denotate and then knock right??
2) if the cam was removed then put back in but no degreed it would cause a knock?
3) if the timing chain had jumped it would knock??
4) if the engine was about to dump because a rod was bad it would knock,\?
5) if its running to lean or rich it would denotate and knock (said something similar to that)
6) timing was retarded or advanced it would knock?
7) and finally just a bad valve would cause knocking??

Are those all ways knocking would happen.. and are there more??

bassman97 · 04-16-2008, 06:15 AM

Yes but retarding the timing eliminates knock, so over advanced timing causes knock. Also, if the cam timing is off, the valves would bend, and you'd notice a very substantial decrease in performance.

JScottGT · 04-16-2008, 06:25 AM

Maybe a better description of the "knock" would help to diagnose the problem.
Pre-ignition or detonation knock has a very particular sound to it and usually only shows its ugly head while driving under heavy load. Kind of sounds like rocks in a blender.
It may also be a spun bearing, whether it is a main or rod bearing, the noise is the same. But this noise occurs all the time, even at idle. It sounds like someone whacking the side of the engine with a hammer on every revolution.

To answer your thoughts:
1) If the wrong fuel was used (not premium) the engine would denotate and then knock right??
Yes, see knock description #1
2) if the cam was removed then put back in but no degreed it would cause a knock?
No, but the performance may be reduced
3) if the timing chain had jumped it would knock??
No, you would have Piston-to-valve contact that would destroy the piston and the valve. Then the engine would not run at all
4) if the engine was about to dump because a rod was bad it would knock,\?
Maybe if it had a bent connecting rod? Did someone ingest water into the engine?
5) if its running to lean or rich it would denotate and knock (said something similar to that)
Yes, see description in #1
6) timing was retarded or advanced it would knock?
Yes, but only if it was waaaay advanced and you were using the wrong fuel
7) and finally just a bad valve would cause knocking??
No, this would just tick

04-15-2008, 04:00 PM	#1 (permalink)
SxyXc Senior Member Join Date: Dec 2006 Location: Texas Posts: 680	What would cause a knock.. trying to help a friend.. He has a knock in his lightning.. the guy before him brought it and had some engine work done, a week after he sold him the car a knock formed. What are causes of knocks? how bad can they be? how can you fix them? Don't know anything but it had work done then a knock formed.. and he can't get a hold of the last owner... I want to know most of the common causes of knocks and how to fix them.. and about the price range.. Thanks in advance Steven __________________ Racing from a roll is just like masturbating, no matter how good you think you are, it is still not the real thing!

04-15-2008, 10:16 PM	#2 (permalink)
SxyXc Senior Member Join Date: Dec 2006 Location: Texas Posts: 680	please tell me if i am wrong on this one. 1) If the wrong fuel was used (not premium) the engine would denotate and then knock right?? 2) if the cam was removed then put back in but no degreed it would cause a knock? 3) if the timing chain had jumped it would knock?? 4) if the engine was about to dump because a rod was bad it would knock,\? 5) if its running to lean or rich it would denotate and knock (said something similar to that) 6) timing was retarded or advanced it would knock? 7) and finally just a bad valve would cause knocking?? Are those all ways knocking would happen.. and are there more?? __________________ Racing from a roll is just like masturbating, no matter how good you think you are, it is still not the real thing!

04-16-2008, 06:25 AM	#4 (permalink)
JScottGT Member Join Date: Mar 2008 Location: Farmington Hills, MI Posts: 62	Maybe a better description of the "knock" would help to diagnose the problem. Pre-ignition or detonation knock has a very particular sound to it and usually only shows its ugly head while driving under heavy load. Kind of sounds like rocks in a blender. It may also be a spun bearing, whether it is a main or rod bearing, the noise is the same. But this noise occurs all the time, even at idle. It sounds like someone whacking the side of the engine with a hammer on every revolution. To answer your thoughts: 1) If the wrong fuel was used (not premium) the engine would denotate and then knock right?? Yes, see knock description #1 2) if the cam was removed then put back in but no degreed it would cause a knock? No, but the performance may be reduced 3) if the timing chain had jumped it would knock?? No, you would have Piston-to-valve contact that would destroy the piston and the valve. Then the engine would not run at all 4) if the engine was about to dump because a rod was bad it would knock,\? Maybe if it had a bent connecting rod? Did someone ingest water into the engine? 5) if its running to lean or rich it would denotate and knock (said something similar to that) Yes, see description in #1 6) timing was retarded or advanced it would knock? Yes, but only if it was waaaay advanced and you were using the wrong fuel 7) and finally just a bad valve would cause knocking?? No, this would just tick __________________ 2000 Mustang GT (aka "The Frankenstang") - 5.4L Power - Comp XE270AH-13 Cams - 261rwhp/330rwtq - 2001 Cobra IRS - 3.55:1 - 2000 Cobra R Rear Springs & Dampers - 2001 Bullitt Front Springs & Dampers - 2001 Bullitt Front Brakes www.jscottgt.com Last edited by JScottGT : 04-16-2008 at 06:29 AM.

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04-16-2008, 06:15 AM	#3 (permalink)
bassman97 blank Join Date: Jun 2006 Location: North Jersey Posts: 1,495	Yes but retarding the timing eliminates knock, so over advanced timing causes knock. Also, if the cam timing is off, the valves would bend, and you'd notice a very substantial decrease in performance.