C2 Heat Riser Valve Operation

[Dave K.]

I recently tested the operation of the original heat riser valve on my 66 327/300 hp SB. The valve moved freely open and closed manually. I drove the car in 90 F. weather about 10 miles. The engine temp was up to about 180 F. Following the drive, I noticed that the valve opened only about 30 deg. but could easily be pushed open manually. Based upon reading previous posts, I assumed that the valve should open fully on its own by means of the thermostatic spring. It should not have to rely on exhaust pressure to open it.

I replaced the valve with a new service replacement but after a similar 10 mile drive the new valve also only opened about 30 deg.

Is the heat riser to open on its own or does exhaust pressure open it? Why is it not opening fully?

Regards,
Dave K.

[Gerard F.]

Re: C2 Heat Riser Valve Operation

Dave,

I think that's the way heat riser valve is supposed to work. At hot idle, they are only about a third of the way open by means of the thermostat spring.
Exhaust pressure at higher revs opens the valve fully. The baffle in the valve is supported by an eccentric pivot. The higher the exhaust pressure, the further the valve opens.

Just give it the gas when you see it only partially open. If you see it open fully on higher revs, then I think you are OK.

Here's a post from the past on my 67 S/B heat riser valve:

https://www.ncrs.org/forum/archive23.cgi?review=192201

Jerry Fuccillo
#42179

[Duke W.]

Re: C2 Heat Riser Valve Operation

Heat riser valves have always been problematic. It rotted out my RH muffler after only five years.

The best thing to do if you don't drive the car in sub-freezing weather is to wire it open.

Duke

[Joe C.]

Re: C2 Heat Riser Valve Operation

Dave,

The valve was designed with an eccentric pivot. Why?
1. It allows some exhaust heat to be sent back "upstairs" during no load operation.
2. It allows the valve to rotate partially and continually during operation, thus retarding (but NOT preventing) the inevitable rust/bind that occurs eventually.

If the valve was intended to open by itself, due to the bimetallic spring force alone, then it would not have been designed with an offset shaft.

Joe

[Gerard F.]

Agree , Joe

The bimetallic spring only opens it up part way, exhaust gas pressure does the rest because of the eccentric pivot. The eccentric pivot provides the opening force against the counterbalance weight when the exhaust pressure increases.

Maybe I'm all wet, but it works that way on my 67 S/B.

Regards,

Jerry Fuccillo
#42179

[Joe C.]

The Counterweight's Mass Actually............

.....provides opening force against the hot spring's closing force, in concert with the vertical component of the gravity vector (32 ft/sec/sec)along its approximately 90 degree arc. The vertical component of that vector is largest when the valve is at or near its fully closed position, and decreases as the valve reaches full-open. That is why the exhaust pressure, working against the offset pivot, is necessary to provide the ADDITIONAL force necessary to open the butterfly completely.

Now..... . If you multiply the average speed of rotation (in rev/min) of the closing butterfly valve by the average closing force of the spring (in ft/lbs), and divide by 5252, then you'll come up with the horsepower of the bimetallic spring.

Joe

BTW: Got my judging sheets back from Marlborough. 98.4% (includes 3 pernts for NCRS decal......no stinkin' cutoff switch ......no stinkin' fire extinguisher ) plus 2.6% for DRIVING .

Total: 100% usable ( 101% actual).

[Dave K.]

Re: The Counterweight's Mass Actually............

Joe,

Now you are talking my language since I have a BSME -- and the BS stands for bachelor of science not bullxxx.

Thanks to all for the clarification.

Dave K.

[Joe C.]

Re: The Counterweight's Mass Actually............

Hi Dave,

Geez, and I always thought that BSME stood fer "Bachelor of Science?.....My Esophagus!"

Mine's a "cum laude", cuz I yell every time I ejaculate.

Joe

[Joe C.]

I Looked at Your Profile.........

Damnnnnn, you own a lot of Corvettes!

Joe

[Gerard F.]

Too theorectical, Joe

Sounds like an ME. Now CE's try to make things simple.

Found a sketch from 1966, here it is:


So if you happen to bump into one of columns at the Newark Airport Terminals, like I did a few weeks ago, just look up. You'll see the hyperbolic paraboloid roof structure. You'll be able to say that you know the guy who researched and devised the practical stress analysis formulas for these structures.

Congrats on your score at Boston. Thanks for the opprtunity to go to Boston with you. The Driving Points probably belong to me (about half)

Jerry Fuccillo
#42179

[Joe C.]

Re: Too theorectical, Joe

Looks like my furnace air filter!

You're very welcome, even though I couldn't fully restrain myself from driving. Next time, you'll have to pry my lifeless digits from the helm.
I'll show you how a McLellan Corvette does donuts, burnouts, and 4 wheel drifts with original tires.

Best,
Joe

[Dick W.]

Re: Too theorectical, Joe

BS=Bull S***
MS=More of the Same
PhD=Pilled Higer and Deeper

[Joe C.]

BS Also Means "Baba Smurf" *NM*

[Chuck S.]

"Baba Smurf"...

I've been wondering where ole Pappy was hangin'...He been keepin' a pretty low profile lately; work pressures I reckon'.