C2:67 Heat Riser Valve

[Gerard F.]

Attached is a picture of my 67 327/300Hp heat riser valve which was recently replaced for the first time with a new exhaust system kit from CC:


The heat riser valve which replaced this original had a slighly larger counterweight, and a second wire spring inboard of the band spring shown in the picture.

My question is, did the original 67 heat riser valve have this second wire spring, or did my heat riser lose it's second spring in the last 38 years?

Also, the new heat riser was installed with the counterweight outboard of the engine (to the right side), as the 67 Judging Guide says. However, I am sure that the original, never been off heat riser was installed with the counterweight oriented to the rear of the car, and it would go down with heat. I remember this specifically when I wired it in an open position.

Is the rear orientation of the counterweight, an anomoly to the Judging Guide?

Jerry Fuccillo
#42179

[Joe C.]

Re: C2:67 Heat Riser Valve

Gerald:

The small coil spring was a poorly desined anti-rattle device. Most, if not all had them originally installed. They were not very effective, though. For that matter, neither was the valve itself, and there were many variations in size and shape, over the years. They never managed to get it right, though, and finally stopped installing them in the late seventies (?).
The counterweight should face the rear, for a smallblock. Other than aesthetics, if there is no clearance issue, and you managed to install it in a different orientation, then it should work OK (as long as gravity acts on the counterweight through the same vector).
I bought two for my smallblock, and they were both different. Was not satisfied with either, so I removed the "butterfly" and cemented it in place.

Joe

[Gerard F.]

Operation of Heat Riser, a Judged Item?

Joe,

Was thinking about doing the same thing with my original heat riser,i.e., removing the baffle and replacing the new one, and back to the original orientation.

Wondering if the lack of original operation would result in a point loss in Performance Evaluation or Flight Judging. Also would the lack of the anti-rattle spring also result in a deduct.

Jerry Fuccillo
#42179

[Joe R.]

Re: C2:67 Heat Riser Valve

Hi Gerard:

I'd like to get clarification on the orientation of your original heat riser. The discussion can get confusing because the counterweight can be mounted inboard or inboard, and the heat riser can be mounted "right side up" or "upside down", depending on which way the weight moves to open the valve.

In the orientation of the heat riser shown in your photo, it appears that the weight would move down to open the valve. So, if the weight was oriented outboard of the engine (on the wheel well side of the manifold) and the weight had to move down to open, it seems that the weight would have to point forward.

I'm curious about this because the above is exactly how my existing replacement heat riser is installed. If it isn't correct I would like to know.

[Joe C.]

Re: Operation of Heat Riser, a Judged Item?

Gerard:

In Flight judging, lack of operation will result in a slight point deduction during the "Operations" phase of judging. Lack of an anti-rattle spring should result in an additional minor point deduction on the "configuration" axis (assuming that your judjes are savvy). Improper orientation of the valve on the manifold (i.e. counterweight facing the wrong way) will result in additional points loss (on the "installation" axis). None of these are very seroius.
BUT, if you wish to PV your car, then lack of operation of the heat riser valve is a "line item failure", which is tantamount to an outright failure. You are allowed one and only one malfunction. If you can fix it, then you can continue the process. If not, then you have failed.

Joe

[John Fowler]

Re: C2:67 Heat Riser Valve

Think you’re upside down.

Sequence is exhaust manifold, heat riser, donut gasket, exhaust pipe. In Gerard’s picture the inner circumference of the riser is beveled to accommodate the donut, so the face shown faces down and mates with the exhaust pipe.

[Joe R.]

Re: C2:67 Heat Riser Valve

Hi John:

Well, the top side in Gerard's photo does seem to expect a donut gasket. I looked at the AIM (section UPC 6, for the engine) and I can see that the AIM says the counterweight should be on the firewall side and that the gasket to the manifold is a flat gasket.

Assuming that the valve is upside down in Gerard's photo, it appears that the counterweight would have to move *up* to open the valve. I was under the impression that the counterweight was supposed to move down to open the valve.

Can someone clarify the intended direction that the counterweight should move in order to open the valve?

[Gerard F.]

Re: C2:67 Heat Riser Valve

Joe,

Sorry I didn't clarify it earlier, company over tonight. The picture is right side up. The dark area which looks like a bevel is flat and is an exhaust stain.
The top in the picture is the gasket side. The tab which supports the spring retainer shaft says "up" on it.

In the picture, the counterweight would go down with heat on it to open the exhaust. The counterweight rotates down about 70 degrees to full open. If installed upside down where the counterweigh would rotate up, exhaust pressure would tend to hold the valve closed due to the offset shaft on the butterfly.

I was wrong about the counterweight orientation, the Judging Guide is correct.
The counterweight on my original was mounted on the aft side of the exhaust pipe, and was pointed outboard from the engine (to the right) when cold.
The shaft on which the counterweight rotates was pointed to the aft of the car, or to the firewall. Rotation of the counterweight is down when hot.

The shop guy who installed my exhaust system rotated the valve 120 degrees forward or counterclockwise. When I questioned the orientation, he told me that the new valve was larger and that the starter heat shield would interfere with the operation. I'm thinking now, that this was just baloney. I'm going to put it back where it belongs.

Please forgive this engineers attempted explanation, and I hope I've clarified the matter.

Jerry Fuccillo
#42179

[Gerard F.]

Re: Operation of Heat Riser, a Judged Item?

Joe,

On PV, do you guys check the exhaust pressure on the right side muffler. That I think, is the only way to tell if the butterfly has been removed. If the heat riser counterweigh went down with heat, and looked like it had all the parts, wouldn't it pass operations. They run better without the butterfly.

Just seeing how far I can go.

Jerry Fuccillo

[Joe R.]

Re: C2:67 Heat Riser Valve

Thanks Gerard. Your expanded explanation is very clear.

How soon do you expect to try rotating your valve to the position shown in the AIM? I'm interested to know the results because my replacement valve is not presently oriented per the AIM and I am tempted to fix it if I can. However, if your mechanic is correct that the replacement valve will not fit correctly in the AIM orientation, I'd like to save myself the effort of trying to rotate it.

[Gerard F.]

Re: C2:67 Heat Riser Valve

Joe,

Within the next couple of weekends if I can get out of my honey-do's. Shouldn't be too hard as the whole exhaust system is new. I went for one of those deluxe aluminized systems from Corvette Central. Everything fit just right except for the heat riser.

I'll let you know. I guess I'm going to nix the idea about cutting out the baffle.

Jerry Fuccillo

[Joe C.]

Re: Operation of Heat Riser, a Judged Item?

Jerry,

It will fail PV. On a cold start, the judge wants to see the valve in the closed position.
During warmup, the bimetal spring relaxes with heat. When that happens, the valve opens partially, so that idling @ operating temperature, it may be 1/4 to 1/2 open. Increasing exhaust flowrates blow it open. If the valve works properly, one should see that action when the throttle is opened.
If you examine the valve, you will see that the shaft does not pass through the centerline of the plate. It is this offset, that causes the exhaust gases to "blow it open". This is what the judges want to see.

Joe

[Gerard F.]

Re: Operation of Heat Riser, a Judged Item?

We'll Joe,

It looks like I'm going to reburb my original and put it back on in the original orientation. On my 67 small block, the counterweight pointed outboard of the engine (to the right) when cold, with the counterweight shaft pointing to the back of the car. It acted exactly like you describe when hot and would only open fully with increasing exhaust flowrate. I thought something was wrong with it for not fully opening on a hot idle.

Are you sure about that anti-rattle wire spring on the originals?

Thanks,

Jerry Fuccillo

[Joe C.]

Re: Operation of Heat Riser, a Judged Item?

Jerry:

Yes. On the valve "stop" pin, there should be an annular groove cut in, maybe 1/8" from the end. That is where the "anti rattle" spring is fastened. The other end of the spring rides on the valve shaft.
If your original valve is not too buggered up, then soak it in diesel fuel for a few days. Every few hours, keep working the valve back-and-forth to dizzolve the rust and carbon. When you are satisfied, media blast the whole magilla, and bolt 'er up.........correctly oriented, of course.
If the shaft and/or housing is worn excessively, then an unacceptable exhaust leak will result. That's your call to make. There should be minimal clearance at the shaft, maybe .005" maximum. Compare the old against the new.

Joe