What Does the Exhaust Heat Riser Do ???

[Joe]

I have a heat riser flapper valve on the right exhaust bank of my
mid-sixties Chevy 327 small block (corvette). Right now it always seems to
stay at the open position.

What does it do and how does it work .... or supposed to work?

Is it to speed up the warm-up of the engine when started cold? If so, the
engine seems to always start and run fine when stone cold so I presume I
should leave it alone and let it stay always in the open position .....
Correct? Or am I missing something here more important?

The details are:

Looking down at the engine, the heat riser valve body is sandwiched between
the right exhaust manifold flange and the exhaust pipe flange. It has an
external lever with an attached thermal coil spring that rotates back and
forth on a shaft that runs straight through the valve body. The lever swings
back and forth over the top and defaults to a position to the left (towards
the engine block while still looking down at the engine). The total travel
seems to be about 120 degrees (maybe less).

Right now it always seems to stay at the open position (default to the left
as described above) unless I manually push and hold it's external lever
..... but then it immediately swings back when I stop pushing it with the
long screwdriver's tip. This happens both when the engine is running or not
and also regardless whether it is cold or warmed up.

The way I determined that it always defaults to the open (left) position was
by feeling the exhaust flow with my hand at the right bank tail pipe (I have
dual exhausts with no cross-over pipe) ..... when I have someone move the
external level to the other end of the lever's travel (to the right) by
pushing on it with a long screwdriver, I can feel that exhaust flow is
reduced.

Any help or suggestions would be greatly appreciated ... Thanks, Joe

[Mike Romain]

It is for faster warm-ups when cold as you thought.

It should be controlled by a bi-metal spring thermostat on the side
where that weight is.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail
88 Cherokee 235 BFG AT's
Build and Canadian Off Road Trips Photos:
(Updated Sept. 05 with Aug. 2001 Canadian Bush Run photos)
http://albums.photopoint.com/j/AlbumList?u=1161190

[Edgar Montrose]

It is a device that is designed to block the exhaust flow
from one bank of cylinders and force it back up through the
head, then through a small cross port in the intake
manifold, into the carb base and then out the opposite
head - all in order to warm the carb/fuel for better cold
starts. After warming up or under more throttle, it is
supposed to open up.

It ain't the greatest design feature of GM engines. Usually,
the thing never gets lubricated and freezes up in the open
position. Also the port in the intake was so small, it
usually carbons up solid from the overrich exhaust. Some
performance intake gasket kits in the past provided block
offs for the port. You could also install small plugs in the
carb base plane holes.

If it works, I'd say leave it alone. If it is broken,
replace or remove it. Unless you live north of the 60th
latitude, it's not any use IMHO.

[Robert Hancock]

It draws air from over the exhaust manifold when the engine is cold in order
to heat up the air entering the carburetor. This is to improve the engine
driveability and emissions in colder temperatures.

--
Robert Hancock Saskatoon, SK, Canada
To email, remove "nospam" from hanc...@nospamshaw.ca
Home Page: http://www.roberthancock.com/

"Joe" <J...@excite.com> wrote in message
news:a7Jv7.87095$QK.50...@news1.sttln1.wa.home.com...

[Edgar Montrose]

Robert,

That sounds more like an exhaust stove used in the later
years, rather than a heat riser valve

[ENomura]

In article <a7Jv7.87095$QK.50...@news1.sttln1.wa.home.com>, "Joe"
<J...@excite.com> writes:

The bimettalic spring and counter weight should close the valve with the engine
off. With the engine running, some of the exhaust gasses should be directed
under the carburetor. As the bi metallic spring heats up, the tension on it is
weakened and less exhaust gas is directed toward the carburetor. The exhaust
gas warms the carburetor to decrease the warm up period and to prevent "icing".
The vaporization of the gasoline at the venturis, lowers the air temperature.
It is possible for your carburetor to freeze the water vapor in the air and ice
at the venturis, restricting air to the engine even when the ambient air
temperature is above freezing. Later fuel injected chevys use the engine
coolant to prevent "icing." If you live in an area where the temperature
doesn't get into the 40's, you shouldn't need this valve. The biggest problem
with this valve is if it seizes in the partially open position. This would
hurt the performance of your car.

Aloha,
Ed
Remove "nojunk" from E-mail address

[Robert Hancock]

Think you're right, I was probably thinking of the wrong thing :-) The
purpose is similar, however..

--
Robert Hancock Saskatoon, SK, Canada
To email, remove "nospam" from hanc...@nospamshaw.ca
Home Page: http://www.roberthancock.com/

"Edgar Montrose" <edgarm...@techie.com> wrote in message
news:n1Kv7.412$4g6.14...@newssvr15.news.prodigy.com...

[Joe]

Thanks to everyone for the info and help ...... I live in a warm So.
California climate so it sounds like I'll just leave it alone in the open
position. The car runs fine as is.

Joe

"ENomura" <eno...@aol.comnojunk> wrote in message
news:20011006234117...@nso-df.aol.com...

[Joe]

Just a quick follow-up question about "being sure it's all the way open".
Does anyone know the correct position of the external counter-weight lever
on the full open position. On my 327 small block with a 1965 Corvette L-79
350HP engine, it seems from the exhaust flow at the right side tail pipe,
that full open is when the counter-weight is hanging horizontally towards
the engine block.

Would that be right? I don't have an example that's not installed to look
at right now and my NAPA auto parts store nor the local Chevy dealer have
one in stock to look at.

Thanks.

"ENomura" <eno...@aol.comnojunk> wrote in message
news:20011006234117...@nso-df.aol.com...

[Mike Romain]

It has almost 90 deg movement. At one extreme the butterfly is closed,
at the other end of the 90 deg arc the butterfly is open. I think the
horizontal set on the weight is right for open from what I remember.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail
88 Cherokee 235 BFG AT's
Build and Canadian Off Road Trips Photos:
(Updated Sept. 05 with Aug. 2001 Canadian Bush Run photos)
http://albums.photopoint.com/j/AlbumList?u=1161190

[Joe]

Thanks Mike ...... That's what mine seems to be like.

"Mike Romain" <rom...@sympatico.ca> wrote in message
news:3BC0B9D9...@sympatico.ca...

[ENomura]

In article <lp2w7.89889$QK.52...@news1.sttln1.wa.home.com>, "Joe"
<J...@excite.com> writes:

I found a heat riser valve and my memory was wrong. The counter weight aids in
opening the valve and the valve is wide open when the counter weight is about
30 degrees from the vertical. There's a notch opposite the counter weight that
hits 1/8" diameter pin sticking out of the heat riser that stops the valve from
opening further. This is the same pin that one end of the bi-metallic spring
is anchored to. Eckler's Vette Parts catalog has a phot of it at the
following url:

http://www.ecklers.com/product.asp?pf%5Fid=A8847&dept%5Fid=159

Hope this helps.

[Joe]

Ed,

I am forever grateful for the link to that photo @ Eckler's.

Just saved me a hour or two tearing mine apart to check it ....... Mucho
thanks!

Joe

"ENomura" <eno...@aol.comnojunk> wrote in message

news:20011008142822...@nso-mq.aol.com...