Drove my yellow '68 to work on Friday and on the way home, the car started making a loud knocking noise.. Sounded like a shot header gasket.. When I checked, the headers on the right side of the car was loose but the gasket seemed ok.. Replaced it anyways and tightened the headers back to the heads.. The noise still wouldn't go away.. It seems to come from the passenger side of the engine.. Could this be a spun rod bearing?? Oil pressure is steady and good..
I did take the valve covers off to check for any issues with a pushrod, valve or rocker arm but everything on the heads looked fine.

Here's the video of the car running.. (video might not be processed yet but should be in a couple of minutes)

 

Hard to tell, but doesn't sound good. Did it start running bad when the noise started or does it run the same as before the noise.

I'd pull the pan and see what it looks like in there

*I put this on all my posts: Please post back to those who helped you, the final outcome of your initial post

 

disconnected one plug on the right side at a time and the noise went away when #8 was disconnected.. Looks like the knock is coming from cylinder #8...

 

I'll let those w/ more experience then I chime in but that doesn't sound like a knock to me.

 

The car ran just the same, I just had the noise.. Performance seemed to be unaffected.. Now that I could pinpoint it to cylinder #8, I'm pretty sure that the engine will have to come out.. I do have my old 406 sitting in my garage (rebuilt) but it has 13.5:1 compression.. Would have to install dished pistons to be able to run pump gas on that engine..

 

Hard to tell, but it still sounds like a bad exhaust leak to me.

 

That's what I thought.. However, this was not the case.. The noise comes from inside the engine.. Exhaust gasket is new and the noise goes away when I disconnect the plug to cylinder #8.. If it was a exhaust leak. that shouldn't make a difference I'd think

 

It sounds like exhaust to me too or something in the valvetrain.

Did you take a close look at your headers to make sure you don't have a new hole or crack- especially on #8? If the plug wire is disconnected on #8 it would be quieter because the fuel/air mix isn't firing in that cylinder. That would explain why the noise went away.

 

A spun bearing should have an effect on your oil pressure. At least make it pulse. Hook a timing light to the motor and move it from plug to plug until it matches your noise.
I have heard a backed out torque converter bolt sound like that in the past.
If you listen to the side of the block with a bar or long screw driver you'll get the sound without the background noise of the engine. The backed out converter bolt will sound like it's coming from the very rear of the block. This is the third thread like this this weekend. Odd.

 

I've got some experience with SBC engine noises nowdays, going to have to agree with others, doesn't sound like a rod knock. Rod knocks are a much more clear, metallic sound.

I recently had a rod knock in my own engine, verified by teardown. Number 1 piston had trashed rod bearings. It had a very distinctive sound. There are a ton of clips on Youtube for rod knock, but this is the only one Ive seen so far representing what an actual rod knock sounds like http://www.youtube.com/watch?v=Vw9KW...eature=related Here's another http://www.youtube.com/watch?v=lrFml3iFBwM&NR=1 . Supras are very prone to rod knock due to contamination of engine oil from blown head gaskets. A very well documented fault but useful as a point of reference for using sounds to diagnose lower end problems.

That definitley sounds more like air being lost either through your exhaust or leaking valvetrain.

It sounds like exhaust leaking. A disconnected plug wire will make an exhaust leak sound go away because combustion is no longer taking place.

Here's what you do, get a piece of tissue paper and hold it near all the joints to see if any exhaust blows on it. If the gaskets are new you probably have a crack in the header somewhere.

Listen carefully as he revs the engine you'll hear it, it's a very distinct metallic sound. Much different than what I'm hearing in your video.

Lower end knocks you can also feel. They will feel like something inside is banging the engine from the inside out.

 

Looks like those who said that it was the exhaust were right.. Not 100% sure yet.. I checked the exhaust gasket again and I noticed that there was still a piece of the old gasket left that caused a leak around cylinder 8. Removed that piece and tightened again and the noise is better but not gone yet.. I might have to pull off the headers completely to clean the old gasket off as it doesn't seem to seal right.. I usually prefer to leave the 2 outter header bolts in place (very loose) so it's easier to tighten everything back up.. Guess I'll have to pull off the headers completely and clean everything before re-installing the gasket.

 

Glad to hear! The only way to get those to seal right really is to get the header off and remove every last trace of old gasket material. A dremel with a small wire brush (use brass brush if you have aluminum heads) makes this pretty quick and easy.

 

Definetly let us know how this turns out, it sounds like its going to be a happy ending!

 

I am 95% sure its NOT a rod knock, or your video sound sucks
It would be very clear and sound like you have marbles in your engine. Something like this http://www.youtube.com/watch?v=DfJIpiQZtR4

S.
ps. Take off the valve cover, maybe one of the rockers is loose...

 

Grand Sport that sounds just like my car, I wanted to post my vid from you tube on this forum. on you tube. ( If you want to look at my vid on you tube type in valve train noise 79 corvette). But my noise is coming from the left side. I removed the plug wire from the #7 cylinder and the tapping noise stopped, Btw in my case when I accelerate, the tapping noise increases. Does the noise increease when you accelerate? I may have a wiped cam lobe. Btw, how do you post a link to you tube on this forum. I would like everyone else to hear it. Also is that a rubber fuel line? If so get rid of it before you have a more serious problem on your hands.

 

lol Damn. Yeah that's the sound. Like two big glass marbles knocking together.

 

What the hell is going on?!?!

I have the exact same symptoms/problem on my '68 327.

Passenger side, knocking/ticking sound very similar to what you posted. I did notice that the middle two exhaust ports, just above where the headers attach, are burnt black due to what looks to be an oil leak from the valve covers. However, I think the valve covers developed that leak, due to the leaking exhaust cooking the gaskets at that spot.

 

That's what I'll have to do... It's just a pain to get those sidemount headers back on once you pull them off.. I guess that I'll have to ask my wife to help to pull up the headers while I'll try to get them back on..

 

Posting a youtube video is easy.. If for example,

http://www.youtube.com/watch?v=pt_X8D52VOQ

is the link to your video, you have to use the youtube tags and the part of the video after the "v=". In order to show the tags, I have to add another symbol.. (I'm using a period which has to be removed in order for it to work)

[yt.]pt_X8D52VOQ[/yt.]


In my case, the tapping noise also increases when accelerating.. Maybe you also have a leak in the exhaust gasket?

The car still has rubber fuel lines.. Will eventually change t hem out to braided ones..

 

An old mechanic's trick

Sound travels through metal or metal and a plastic handle. Place the biggest screw driver you have against various places on the heads and block and put your ear to the plastic end. You can move it around and pick out individual items.

I had what I though was bad rod knock once and it turned out to be failed Keith Black Hyper pistons. Good oil pressure and when listening with a screw driver you could tell it was higher in the block and on three of cylinders