Technical Exhaust Header Knock

Is there such thing as a Header Knock? I recently 401 nailhead out for a 425, using the headers the were on the 401. When I get on it when the engine is not up to temperature,
there is a knock or rattle that comes from the exhaust, it goes away once the engine is up
to temperature. I never experienced this on the 401. Cam anybody explain this.

 

Something loose or broke? When heated up it expands and gets less noisy , not gone.

 

Does the header have a heat riser?
don

 

Could it be better exhaust port scavenging causing a lean condition?


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Piston skirt knock, goes away when warm, SBC are famous for this.

 

Sounds like a main

 

I had 1 Exhaust valve Guide go bad that made a knocking sound , the sound was the Valve centering its self on Valve seat when closing.

 

Not sure if this applies to any of you. But my hearing has deteriorated with age. A couple of years ago, I could hear this god awful clatter coming out of my sbc. Sounded to me like I'd done a big end bearing, although oil pressure was still good.
Not having time to mess with it, I quickly fitted a new crate engine.
Fired it up. Much to my horror, the noise still there.
So I asked Mrs to listen while I revved it up.
She thought the noise was coming from further back towards the middle of the truck.
Turned out to be a loose baffle in one of the mufflers.
Never did tell her the whole story!!

 

This s a brand new rebuild by Russ Martin of Centerville Auto. I swapped all the bling and headers off my 401. The headers are long tube and have no loose ends in them. Could it be that there is a different cam in the 425, which incidentally is bored out to 435 cubes. The noise didn't happen with the 401, and only happens when I put my foot into it and its not up to temperature.

 

I've had a small exhaust leak that sounded like a knock that went away when it warmed up. The metal expands and sealed up the leak, warm it up and put a wrench on each bolt, let it cool and wrench them again. That's how I got mine to seal.

 

It’s never a good idea to put your foot into it before the engine has some oil temp. If it has forged pistons it could definitely be the noise until they warm up & expand a little.


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