jimh_1962

I guess that's my point all of the long the shop should take on the tear down. I think the OP has done enough. At some point the engine needs to be looked at by the builder.

Frankie the Fink

400 hundred miles on the rebuild folks.

I'd dump it right back on the shop that did the work...
Start dropping pans and popping rod caps off and guess who now owns the problem ?

jimh_1962

Yeah, take it back!

67 Fuelie

Check for a loose spark plug.

SDVette

I like the RandyG description of rod knock detection.. Hope I never have to use that one.

No ignition, no noise.

I'm holding out hope that is IS an exhaust leak, either at the head, or spark plug.
Exhaust can sounds pretty metallic sometimes...

But I agree that the machine shop who did the rebuild should diagnose it now.

Randy G.

Excellent. Please let us know what they come up with.

SDVette

I"m not the original poster... just adding my opinion to the soup!

pop23235

Unless you want to really "own it", it goes back exactly like you picked it up.

Ktholin

Update: First of all, thanks to all the forum members who have chimed in on this. I am really appreciative of all of the ideas and input from each of you, and I have learned a lot in the process. I have spent the better part of the past 4 years on this restoration and just recently "completed it". I was hoping that this summer would be spent cruising, but here I am...

So, I spoke at length again with the rebuilder today. Seems like "a short while ago" was more than that. I had the engine rebuilt earlier in my project, so it is technically beyond the 12 month, 12,000 mile warranty period, even though I have less than 400 miles on the motor. However, the builder understands the reality of restoration projects. He said, "Maybe not free, but I will work with you." I'm happy with that. He's a reputable builder here in So Cal.

Another interesting finding was that the spark plug in #4 WAS loose, but, alas, the sound persists.

I made a video which I think illustrates well the sound and the "spark/no spark test". You can see/hear it via the following link:

https://keiththolin.smugmug.com/Corvette-Engine-Noise

I'm going to check the oil tomorrow and maybe drop the pan. I'll keep you posted. Pulling the engine is the last resort, so I want to rule out as many other possibilities as I can. Thanks again to all of you.

SDVette

Great video.
I'm sticking with my exhaust theory... Keep us posted!

Westlotorn

Beautiful car. Reading this I was leaning toward rod knock or piston scuff.
After listening to your video and seeing your headers I lean towards a tight or bent exhaust valve in number 4 cyl.

MikeM

Me too but this would be better to hear the noise first hand.

First guess, I didn't know you had headers with the individual tubes on each port. Now that I see the headers with the individual runners makes me more convinced it's exhaust.

You could put a shot of oil in the intake while the engine is idling and watch for a puff of smoke around the header flange.

Frankie the Fink

Yeah, which is prob better than bottom end problems...

You get extra points for the ***** to take a plug wire off with bare hands....

I have an insulated tool for that...

wraplock

when you adjusted the #4 lifter did it quiet down for a short period of time? Ask your rebuilder if he installed new rocker arms and nuts, I've had worn rocker arm nuts that wouldn't hold adjustment and kept getting loose until I changed them out. When I ran a solid lifter cam in my 62 I used Poli-loks on the rockers.

L78racer

sounds like exhaust noise. header has a hole or crack? intake crossover at head?

jimh_1962

Do you have a vacuum gauge and a stethoscope?

You can spray some soapy water around the headers #4 exhaust and see if it there is a leak near the flanges. That should tell you whether or not is it an exhaust leak on #4. I changed to poli-loks... It really helps keeping the rockers from getting too loose.

Listening to the video helps!

Ktholin

Yes, I do.

GTOguy

Great video! And it helps a lot. If it's any consolation, I have never, ever, heard a rod knock sound like that. It sure sounds like an exhaust leak to me, too. Back the timing off (retard it bout 10 degrees) and see if the noise changes....if it does, most likely an exhaust leak.

karkrafter

Exhaust leak I'll bet... Take it outside at night in as dark of a spot as you can find, do it then, revving it up....it may become evident to the eye.

Ktholin

When you say exhaust leak, are you referring to a leak at the header gaskets?