Heat Riser Does Not Open on 72'
Thread Starter
Intermediate
Joined: Dec 2012
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From: Greer SC
Heat Riser Does Not Open on 72'
I confirmed the heat riser on my 72' never opens. All the components (i.e. spring) appear to be there, but there is no exhaust out the passenger side even after the car is warm. The counterweight is always in the up or horizontal position (riser butterfly closed).
When I hold the counterweight down (riser butterfly open), exhaust comes out the passenger side, equal to the drivers side like it should.
Why/how in the world did GM design the riser to fail closed!?!
Also, I know I can wire the valve open, but do any of you have an idea what might be wrong with it? Like I said, all of the parts appear to be there and hooked up.
When I hold the counterweight down (riser butterfly open), exhaust comes out the passenger side, equal to the drivers side like it should.
Why/how in the world did GM design the riser to fail closed!?!
Also, I know I can wire the valve open, but do any of you have an idea what might be wrong with it? Like I said, all of the parts appear to be there and hooked up.
Team Owner
Joined: Sep 2006
Posts: 31,274
Likes: 4,366
From: Westminster Maryland
Hi zz,
One thing you can try is to determine if the bi-metallic coil is there and that one end (the outer) is attached to the peg with the spring, and the other end of the coil is inserted in the slot of the rod that the flappers that control exhaust flow are attached to.
Regards,
Alan
One thing you can try is to determine if the bi-metallic coil is there and that one end (the outer) is attached to the peg with the spring, and the other end of the coil is inserted in the slot of the rod that the flappers that control exhaust flow are attached to.
Regards,
Alan
Team Owner
Joined: Jul 1999
Posts: 65,492
Likes: 230
From: Orange Park Florida
Alan above is correct, but how many of our beloved sharks are driven in sub freezing weather??? so to just wire the thing open, or twist it that way, and release the spring, carb/induction will warm up almost as fast, talking maybe a minit here now....
for that matter, I have filled the up/over passage in many a intake mani to block it off with Plaster of Paris.....maybe leaving the intake open enough on the pass side to ensure heat flow to the choke apparatus.....
BUT to keep the carb from frying when the temps outside are ~100f.....
for that matter, I have filled the up/over passage in many a intake mani to block it off with Plaster of Paris.....maybe leaving the intake open enough on the pass side to ensure heat flow to the choke apparatus.....
BUT to keep the carb from frying when the temps outside are ~100f.....
Thread Starter
Intermediate
Joined: Dec 2012
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From: Greer SC
Hi zz,
One thing you can try is to determine if the bi-metallic coil is there and that one end (the outer) is attached to the peg with the spring, and the other end of the coil is inserted in the slot of the rod that the flappers that control exhaust flow are attached to.
Regards,
Alan
One thing you can try is to determine if the bi-metallic coil is there and that one end (the outer) is attached to the peg with the spring, and the other end of the coil is inserted in the slot of the rod that the flappers that control exhaust flow are attached to.
Regards,
Alan
I still can't believe it is designed to fail closed...perhaps something is installed wrong...
Last edited by ZZtop2; Jan 19, 2014 at 05:44 PM.
Burning Brakes
Joined: Jan 2006
Posts: 1,073
Likes: 331
From: Clear Lake Shores Texas
2016 C3 of Year Finalist
I agree with Mike Ward. The heat riser on my 72 is closed at idle even when the engine is at normal operating temperature. The increased exhaust flow when engine RPM's increase allow it to open.
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Thread Starter
Intermediate
Joined: Dec 2012
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From: Greer SC
Interesting. I rev'd it pretty good and didn't see it move. I also have the classic symptoms of it staying closed: paint burning off the intake manifold at the cross-over tube. I will take another look and then try pulling the coil spring like Alan suggested and see what happens. Thanks guys.
Race Director
Joined: Jul 2001
Posts: 15,892
Likes: 42
Interesting. I rev'd it pretty good and didn't see it move. I also have the classic symptoms of it staying closed: paint burning off the intake manifold at the cross-over tube. I will take another look and then try pulling the coil spring like Alan suggested and see what happens. Thanks guys.
Drifting
Joined: Mar 2011
Posts: 1,886
Likes: 9
I messed with mine for years. I drilled and tapped the counterweight and bolted on extra weight in an attempt to get it to be open more often.
Finally, I changed over to an aluminum manifold and swapped out the heat riser for an open spacer.
Finally, I changed over to an aluminum manifold and swapped out the heat riser for an open spacer.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
If you don't NEED the heat riser (car seldom used in very cold weather), just drop the exhaust pipe from the heat riser and cut the butterfly valve off the shaft. That way, it can NEVER be closed on you!! And, you don't have any bailing wire showing.... 
Burning Brakes
Joined: Sep 2005
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From: Lewes Delaware
Thread Starter
Intermediate
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From: Greer SC
Update: I unhooked the bi-metallic coil spring to drop the counterweight down (open the butterfly valve) as suggested and then just wired the counterweight in position so it does not bounce around over bumps in the road. It worked great and the car still starts fine on cold mornings. Thanks for the help guys.
Thread Starter
Intermediate
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From: Greer SC
Tom, I still have the new Rev100 Classic wheels on it and it is running and driving great. I have done a lot to improve the driving experience without altering the originality of the car (i.e. only bolt on changes like shocks and composite rear spring with 10" lowering bolts, no cutting/grinding/welding except for relocating the rear parking brake bracket on the trailing arm for wheel clearance).