I got a noticeable knock coming from the engine and i can't seem to get rid of it. this is what i've done so far:

I've advanced and retarded the timing as far as it goes in both directions, with no change in sound. I thought maybe the dist was off a tooth, but at TDC, the rotor is pointing exactly at the #1 cylinder (i broke my timing light so i couldn't check like that last night, new one will be here tomorow). I'm 95% sure the dist is where is was supposed to be.

Thought it might be crap gas, so i drained the tank and put some sunoco 94 in, did nothing. Added a can of octane boost, making the octane level about 96~ did nothing.

Thought maybe one of the accesories was out of whack, so i took the belts off and ran it for a few seconds, no change in sound.

I'm just about running out of ideas here, the A/F meter shows a slightly rich condition, so it's not leaning out, and the headers are not glowing.

The only idea i have left is that maybe it the plug wires. The #6, and 8 cylinder plug wires are not only touching, but there more or less crammed together in an attempt to keep them from burning on the header. I've got new wires and 1400* protector sleeves on the way to eliminate that situation.

I also just read someone elses post about a knarled up fuel pump rod, and it possibly causing a knocking sound. This strikes a cord because on two occasions i have started the car with the fuel line plugged, after the pump (forgot to hook it back to the carb). I imagine that puts a lot of stress on the pump cause of the pressure build up. If anyone thinks that might have something to do with it, i'll go take it out and have a looksee.

The only other thing i have determined is that one of my old valve covers was warped, so i took it off and corrected the problem with a 10 pound sledge hammer. unfortunately the cover couldn't withstand the pressure from the sledge, and exploded into several bits of flying shrapnal. But don't worry, no one got hurt, and the new valve covers will be tomorow

I'm just about stumped on this one and could use some help... before i drive this thing off the pier...

heres the setup if it helps out any:
Trick flow 23* heads with 1.47" springs
roller tip 1.6 rockers and 7.85" pushrods
crane 272H cam (w/ 1.6: .484/.484 218* dur)
edelbrock performer intake
non cc Qjet carb and dist. <---------------------could this have anything to do with it?
edelbrock TES headers.

I think that covers the important stuff...

Oh yeah, one more thing, the knock seems to get quieter once the engine is hot, either that or it seems to get quiet after i take it out and romp on it at WOT several times...

Any ideas? And i do mean ANY

Eric

 

I'm a little confused. Does the engine knock all the time or only under a load? Preignition or detonation (from excessive timing advance) would normally only occur under an acceleration load. A mechanical noise could produce a sound whenever the engine is running, loaded or not.

Any hints?


BTW - Don't go near the water...

 

the engine knocks very slightly at idle, gets louder when i hold it at about 2000~ rpm, and gets quiet under full load (WOT). Actually it may be that i just can't hear it over the exhuast at WOT....

does that help at all?

 

Usually if you have a knock that just won't go away, it is a bearing of some sort that is losing its tolerances

However, it might just be a cam bearing slightly out of spec and the engine will still run for a long time.

Or it can be piston slap, which is annoying but will not kill the engine for quite a while. Usually piston slap goes away when the engine is warm though.

 

i'm gonna pretend i didn't read that. "think happy thoughts, think happy thoughts..."

please tell me your mistaken on that...

Eric

EDIT: tell me more about this piston "slap". my knock seems to go away, or at least get quieter as the engine gets hotter, which seems somewhat familiar to what your saying...

 

Not much more I can say. Forged pistons are notorious for slap. The LS1 engines are also known for that problem.

 

don't have forged pistons. what exactly is piston slap though? theres gotta be something hitting something for there to be a slap correct?

 

i took the fuel pump out to check for that and it looks fine as does the rod, so i guess we can rule that out.

I did stumble across something else though, It was my understanding that when i set the valve lash, i was supposed to set them to zero lash, and then go a 1/4 turn furthur. When i did this the rockers became really tight, and i couldn't rotate the pushrod. I did this last week. Well today i brought the motor to TDC just to check them out, and they all feel like they are still at zero lash, being that i can rotate the pushrod. I can feel some resistance when i turn it, but i still can do it. I shouldn't be able to do this if i adjusted them past zero lash should i? does that make any sense at all? I just tightened them all an additional 1/4 and they are tight again, but i haven't started the car yet (no valve covers or wires) so i don't know if it made a difference or not...

any thoughts?

Eric

 

They shouldn't be spinning from my knowledge, as far as I know.

 

Try disableing the spark on one cylinder at a time.
(pull off a spark plug wire) is the sound stops on one cylinder
you have a bottom end problem ( piston, pin, rod, bearing, main)
If it continues while doing this it's valvetrain , fuel pump or flywheel.

 

Piston slap occurs when the piston is marginally smaller than the cylinder bore, which allows the piston too much movement from side to side. That is the slapping/knocking sound. It plagues forged pistons because they must be forged a tiny bit smaller than cast pistons, because they expand at a different rate when heated. Otherwise they would bind in the cykinder bore and bye-bye engine.

 

It could maybe possibly be a loose rocker arm?

 

if its a valve its more of a tick then a knock.. a knock might be a rod going.. but if what your experiencing is a valve tick its little more then a simple adjustment.. get 2 old shirts or rags and lay them on the manifolds, headers and start the car without the valve covers on.. get real close to the rockers with your ear or take a piece of tubing hold one end to your ear and the other near each individual rocker.. if the sounds you are experiencing is coming from there its simply out of adjustment valves.. loosen the bolt until the clacking becomes loud and then slowly tighten until all sound stops and then tighten 1/4th of a turn and your valve is in adjustment. this must be done with the engine running.. try not to get too much oil all over n if you have the engine running for about 5 mins or so shut it off and let it cool down.. your rags are gonna catch on fire

 

also have u tried grounding off cylinder by cylinder? if you do and the noise stops you have a rod knock on that particular cylinder..