# Exhaust Manifold heat riser flapper thingy?????



## Lawddog (Jan 2, 2020)

Ok fellas, 
I have another question for you. So i was getting this knock from the passenger side of my 66 GTO and i while i was at the exhaust shop and the car was on the lift, we noticed this little flapper thingy (my technical term for it) was making the knocking noise... My question is, how do you get it to stop? 

Right now i am looking for a fix that may be temporary, i dont really want to pull off the manifold, remove it and have the wholes welded up. im probably going to replace the whole thing with a Ram Air Manifold but until i do, i need something to stop that racket... 

Thanks in advance...

V/r Jason


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## Jim K (Nov 17, 2020)

Your description sounds like the exhaust heat riser valve. If it's just flapping then chances are it's missing some parts. Early versions were thermostatic spring actuated. Most people just took them off at some point.


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## Old Man Taylor (May 9, 2011)

It should have a weighted lever on the side. If so you might be able to temporarily wire it open. Also you could get someone to tack weld it open. Make sure it is open!


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## Lemans guy (Oct 14, 2014)

Agree with Mr.Taylo,....just wire or weld it open....I hate those things always removed them. They operate on a thermostatic spring like a choke when cold the spring contracts and block the passenger exhaust. That then sends all that exhaust through the intake manifold exhaust crossover which runs under the carb. It heats up the carb faster in cold weather and then as exhaust manifold heats up the spring expands and opens the flap for the rest of the driving trip.

Just tie it open won’t effect anything, exhaust heat will still go under the carb at the crossover, just not as much.


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## wkradem (Feb 8, 2021)

posted the wrong thing sorry


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## Lawddog (Jan 2, 2020)

So my next question is what would be considered "Open"? is it when it is sticking out, or when it is up against the manifold. I would think that it would be when it is sticking out but i want to be sure.


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## Lemans guy (Oct 14, 2014)

Look at some photos of those, just google GM heat riser valve.....basically if you drew a straight line from the hinge center through the weight......that line is the same as the flap plate inside.....so look at it along that line.....


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## Indy1K (May 16, 2008)

In regard to the heat riser flapper valve. Does anyone have a picture of how the bi-metalic spring and anti-rattle spring are mounted? My mounting post was worn away. I drilled and tapped it for a post. Now I need to know how the spring are attached.

Thanks


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## GTOJUNIOR (Aug 7, 2011)

There are/were two posts/rods with grooves at the end of each.
The Thermo spring has a flat tab that slips into the larger post/rod and then is clocked around
and hooked over the smaller post/rod.
The anti-rattle spring is then just clipped on in the grooves.

Here is a page from the SM and a mock-up on a '66 OHC but the basic layout/installation should be the same.
Disregard the Thermo spring cover as I think that is only on the 6.

I hope this makes sense and is of some help.


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## Indy1K (May 16, 2008)

GTOJUNIOR said:


> There are/were two posts/rods with grooves at the end of each.
> The Thermo spring has a flat tab that slips into the larger post/rod and then is clocked around
> and hooked over the smaller post/rod.
> The anti-rattle spring is then just clipped on in the grooves.
> ...


Thank you, that helps.

Kev


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## Indy1K (May 16, 2008)

So, after all the discussion, drilling and tapping where the rod used to be, putting a screw into the rod location and getting the springs on there, I decided to use my other manifold that doesnt have the heat riser butterfly in it at all. I ran a threaded rod thru it and double-nutted both ends thus sealing the two holes. Since I live in SW Florida, I will never miss it. Now, what to do with this other manifold? Probably sell it. 

Kevin


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