Heat riser valve...
 

On my 67 L6 the thing flops back and forth as soon as I crank the engine...it’s also in the general vicinity where I’ve located my manifold leak. The coil spring isn’t broken - I can operate it by hand with the engine not running. Anyone have any experience or thoughts about this????

Re: Heat riser valve...
 

Ok, it’s not flopping so much as vibrating a bit...and the knock doesn’t go away when I push it open or closed while the motor is running, so it’s back to the diagnostics drawing board for me....

Re: Heat riser valve...
 

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Sounds like it is working correctly but maybe the spring is weak. The pressure from the exhaust has to open it some when it is cold so there is no back pressure, so it should open a little every time an exhaust valve opens. When the engine is hot the coil spring expands and holds the valve open all the time. If you open it by hand when the engine is cold it should rotate back to the closed position when you release it.

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Re: Heat riser valve...
 

Thank’s for the reply! It does rotate back when I open it by hand, but the spring seems kinda weak - I had never noticed the thing until I started looking for the manifold leak.

Re: Heat riser valve...
 

Mine was leaking there too. I replaced the whole manifold with aftermarket. But I believe you could re-bushing the shaft to cure the leak.

I got a great deal on the aftermarket manifold...so instead of trying to fix it, I replaced it.

You can find my review on Amazon
https://www.amazon.com/ATP-Automotiv...ws/B000IYCY3E/

Re: Heat riser valve...
 

That flapper is in there to either allow hot exhaust up to the bottom of the intake or shield the bottom of the intake from the hot exhaust.

I recall a past thread where someone said they removed the shaft and drilled and tapped the holes for plugs, or maybe they locked the flapper in place and sealed up the holes somehow.

Re: Heat riser valve...
 

It helps heat up the engine so you get up to operating temp sooner, for better mileage. If you want to delete it, you can just put a bolt all the way through with a nut on the far side. That way you won't have to tap the manifold. A bolt will offer no more back pressure than the shaft and straight flap would.

Re: Heat riser valve...
 

Thanks for the explanation! I have been trying to figure out what this thing is (newbie over here)! Mine at some point was pulled open and is being held open with bailing wire. Ugh. I’m guessing it has a weak spring and we’ll be looking to replace it.

Re: Heat riser valve...
 

No problem. It's actually a pretty simple device once you understand it.

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