[strengines]

i have a knocking sound in my motor. it happens at idle in nutral (its a stick) if i rev it with no load, the knock goes away right off idle, if i am driving the car, i can hear the knock going through the powerband...any ideas?

its a 350

mike

 

[Mike]

This been going on or just start ?
As it occurs at idle ,try pulling the plug wires out of the cap 1 at a time until the knock quits.
That'll narrow if it's from a particular cylinder.

 

[strengines]

i just bought the car and the owner said it has been doing it for awhile...judging by what you said your feel it could be a rod knock?

 

[Mike]

You did say knock not tap ,so it's a process of elimination as I can't hear it.
Go buy a mechanics stethoscope to narrow down the location.
Might also take the front drive belts off and see if it stops.
Cut the oil filter open and see what you can see in the bottom.
Just do one thing at a time.

 

[strengines]

awesome, ill try the spark test tomorrow morning (the next chance to work on the car) and let ya know what i find. its really hard to narrow it down with a scope, i tried that, only thin i could figure was that it wasnt any of the accessories. however, i did not check the fuel pump

 

[Mike]

Just be sure to pull the wires from the cap not the plug.

 

[TooLgasm]

I had a harmonic balancer coming apart which made a definite knock at idle and under load. Turned out the previous owner neglected to use loc-tite on the hex screws when assembling.

Also had a rocker hitting my aluminum valve cover... had to grind the cover down. That sounded more between a knock and a tap. Good luck.

Brian

 

[strengines]

alright, so i fooled around with it here is what i got...

i did the spark plug wire test, the knock still existed. i checked all cylanders. i got the scope out and checked further. the fuel pump is making noise, but i dont think thats it...i put the scope on the drivers side valve cover, twards the front, and i hear it pretty loud, put it to the back of the same cover, and i hear it, not as loud as the front. pass side, i only heard it slightly, i put the scope on the block, same thing, heard it slightly from both sides...as with the heads. i heard it pretty good from the timing cover, but everywhere else was just as before...i can hear it everywhere, but not as loud as the valve cover, or the timing cover. hoping i narrowed this down to a drivetrain noise?

what would a wrist pin sound like? or a skirt starting to crack?

i have all new valvetrain parts waiting to go in, as well as heads. i just dont want to throw them on and have it be something in the block.

thanks

mike

 

[Mike]

Would have reduced the noise with pulling the plug wire on the cylinder causing it.
Don't replace "stuff" until you find the source of the knock.
Pull the valve covers and see what you find.

 

[webfoot]

I had a harmonic balancer coming apart which made a definite knock at idle and under load. Turned out the previous owner neglected to use loc-tite on the hex screws when assembling.

Also had a rocker hitting my aluminum valve cover... had to grind the cover down. That sounded more between a knock and a tap. Good luck.

Brian

I had this same problem - if removing the plug wires didn't help the sound this is still a possibility.

 

[strengines]

i had that valve cover of the other day, what should i be looking for asside from marks on the valve cover?

mike

 

[strengines]

whats the best way to check the balancer? just check that the bolt is tight?

mike

 

[TooLgasm]

i had that valve cover of the other day, what should i be looking for asside from marks on the valve cover?

mike

You would definitely see wear marks on the inside of the valve cover. Mine had one and was visible on the rocker making contact too.

 

[strengines]

awesome, ill check that tomorrow

 

[TooLgasm]

whats the best way to check the balancer? just check that the bolt is tight?

mike

A visual inspection while the car is idling might tell you... if not, to be sure just remove the belt and see if it wiggles. Mine is a two piece SFI balancer, which I needlessly removed thinking it was bad... I just had to loc-tite and re-tighten the hex screws on the balancer itself. Noise gone!

 

[webfoot]

If you have the valve cover off while its running, and you don't hear the noise - or if you don't want to make a huge mess, remove the bolts and slide it up a little bit so there's more clearance in the back. That is how I discovered that my problem was not related to mal-adjustment.

 

[kettbo]

The rt corner of my frt bumper has a small bend...touches the bottom of the fender extension of my 70 Elky. Causes the frt of the passenger inner fender to vibrate and makes a knocking sound. Apply the slightest pressure to the frt bumper, the noise goes away.

 

[65cayne]

.... the fuel pump is making noise, but i dont think thats it...i put the scope on the drivers side valve cover, twards the front, and i hear it pretty loud, put it to the back of the same cover, and i hear it, not as loud as the front. pass side, i only heard it slightly, i put the scope on the block, same thing, heard it slightly from both sides...as with the heads. i heard it pretty good from the timing cover, but everywhere else was just as before...i can hear it everywhere, but not as loud as the valve cover, or the timing cover. hoping i narrowed this down to a drivetrain noise? ...

Why dont you think it is the fuel pump? If it is mechanical, maybe the push rod is going bad?

 

[Mike72ss]

I am having a very similar situation with my 68 Camaro. At first I did the spark plug wire test and had the same "knocking sound" as before. (thank God) I too used a stethoscope and found it let you hear almost too good to pinpoint the problem. I then took off the alternator belt and the sound went totally away. So now I am down to either the alternator or the water pump. I am leaning toward the alternator since I feel a little lateral play, although the pulley seems to spin fine by hand, it is about 18 years old. (I don't drive it much I guess) The water pump is only a couple years old. So I'm going to get a new alternator and cross my fingers.

Did you try pulling your belts yet?

Mike

 

[strengines]

ah i didnt have a chance to tackle it today, tomorrow morning i will make it a point to do it.

about the fuel pump...should i be hearing it if i put the scope on there? is there any way to test asside from removing it?

i will also try removing the belts tomorrow, ill post as soon as i check these things. great input.