Hello all,

Edit: Heres a link to the video. Changed manifold gasket, no change. Noise seems to be getting worse so I guess it's time to pull the heads.


Sorry for the length...trying to get all the useful info in one post! I have a TSP 418 LS3 in my '69 chevelle. I had some broken valvesprings last year when they went through their bad .675 EHT spring issue. They sent me new .660 springs and they have been great since (running their 235/239 cam). The motor has about 15,000 miles on it with only street driving, no track nearby.

Coming back from a road trip recently on the highway I started getting a strange metallic scraping noise that I immediately thought was either driveshaft just touching the exhaust or maybe a pulley/idler bearing going out or maybe even some debris wrapped up on something and smacking. The noise did change with RPM. After a couple minutes it went away completely and since we were close to home we kept going. Oil pressure and power were good. I took it out the other day and it was fine for maybe 30 min and I forgot about it...then suddenly after a WOT blast the noise was back and stayed all the way home. It almost seems worse at idle but maybe I can just hear it better. I pulled the valve covers and no problem, springs and rockers are good and turning it over by hand there were no noises...although with it being intermittent who knows.

Running it up n the lift the noise seems to be coming from inside the engine rear couple cylinders on passenger side...basically up above the starter motor. It sounds like a metallic scape or rather than a knock. Is it possible the windage tray has shifted a hair and it touching a counterweight after 3 years? I'm leaning toward lifter but is it possible for that to come and go like this? Started it on the lift yesterday to get a video and it wouldn't do it except just as the motor shut down it would make the sound once before stopping spinning.

Anything else to check before pulling heads?

 

Forgot to mention...whatever it is also drives the knock sensors wild when it happens. After listening to lots of videos I guess it could be an exhaust leak off the header flange but would that come and go...and trigger the knock sensors?

 

Check the harmonic balancer, it will drive the knock sensors bananas if it is falty, ask me how I know!!

 

Worth a look but the sound is definitely further back. I have it up on a lift sitting under it so it's pretty easy to locate the general vicinity. Going to change the header gasket tomorrow and hope.

Anyone know if a bad lifter will make an intermittent noise? I would think it would be more constant but????

 

Yes it can. But how intermittent?

 

Like drive for 30 min with no noise then suddenly start. It was doing it yesterday on the lift, shut it down to go get my phone for a video then it wouldn't do it again despite running for another 15 minutes. Weird.

 

First post updated with video. Changed header gasket and no change as expected. The car runs perfectly until it's hot and you do a hard pull then it starts doing it. Seems to be getting louder so I guess the heads will come off.

 

Just to follow up on this, yes indeed, a bad lifter can come and go randomly. Pulled the head and one roller is basically square, cam lobe chewed up by the look of it. Now the decision to pull and rebuild or just new cam and lifters. Motor only has 15k on it and my shop isn't big enough to pull a motor in.