Heat riser stuck closed
So, the heat riser is stuck shut in my '67 L79, what damage will be done if I don't wire it open until I get a replacement that works as it should?
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Big Tanks In the High Mountains of New Mexico -
Re: Heat riser stuck closed
When the heat riser was operating correctly the exhaust was routed across the engine to heat the carb, until the riser damper opened, so things are designed to handle the heat. Long term you'll probably experience a hot carb and engine running issues... due to the excessive heat.
If you can move it, I'd wire it open and forget it.... unless you are worried about judging. -
Re: Heat riser stuck closed
Pull it out and soak in EvapoRust for a few days and reinstall or buy the replacement spacer (w/o the butterfly) from one of the vendors.Comment
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Re: Heat riser stuck closed
IT will boil the fuel in the carb...James A Groome
1971 LT1 11130 - https://photos.app.goo.gl/zSoFz24JMPXw5Ffi9 - the black LT1
1971 LT1 21783 - 3 STAR Preservation.- https://photos.app.goo.gl/wMRDJgmyDyAwc9Nh8 - Brandshatch Green LT1
My first gen Camaro research http://www.camaros.org/forum/index.p...owposts;u=4337
Posts on Yenko boards... https://www.yenko.net/forum/search.php?searchid=826453Comment
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Re: Heat riser stuck closed
Happened often "back in the day" - we'd spray 'em with PB-Blaster or Liquid Wrench and work them by hand until they were free and operating correctly - UNLESS the spring or counterweight are messed up - then its best to wire it open. Aircraft safety wire is what I use and I've run with all of mine wired open (in Florida) for 20 years. You do NOT want to operate the car long with one stuck closed - you will percolated your fuel and you'll basically be running with a restricted exhaust system...Comment
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Re: Heat riser stuck closed
Even when fully "closed" there is some space around the butterfly for some exhaust gas to escape into the exhaust system. But, with that HR butterfly in the closed position there is a considerable restriction of normal flow of exhaust. When the engine is up to full normal operating temperature heat that is not flowing through the exhaust system as designed has to go somewhere. In addition to problems already mentioned, there is a risk of burned exhaust valves and a blown head gasket on the cylinder bank that is restricted. The good news is, it is a relatively easy fix even if you have to remove it and replace it with a new one. If you have to remove it - plan ahead regarding the removal of nuts off of the exhaust manifold flange. Chances are, if the HR was left unattended long enough to freeze up, the nuts on the exhaust flange are on there pretty good too and there is a risk of breaking a stud. I would attack it as if it were frozen on - soak in penetrating fluid as much as possible and apply some heat with a torch - assume it is frozen. Good luck.EdComment
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Re: Heat riser stuck closed
While there are risks...
A car I work on had a rattle that the owner could not get diagnosed. He brought it to different mechanics with no success at getting rid of it.
Turns out when his exhaust was replaced about 30 years ago they put the heat riser in upside down, so it effectively remained closed as long as he owned the car. And, it then rattled.
He's much happier with a correctly installed heat riser, and the engine runs just fine. As you may guess, the rattle is gone.
PatrickVice-Chairman (West), Michigan Chapter NCRS
71 "deer modified" coupe
72 5-Star Bowtie / Duntov coupe. https://www.flickr.com/photos/124695...57649252735124
2008 coupe
Available stickers: Engine suffix code, exhaust tips & mufflers, shocks, AIR diverter valve broadcast code.Comment
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Re: Heat riser stuck closed
Thanks all, the lever and counterweight operate freely, it just will not open when it heats up. Think I will wire it open until the replacement unit arrives for me to install.Big Tanks In the High Mountains of New MexicoComment
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Re: Heat riser stuck closed
Time and thermal cycles take a toll. It may not be worth replacing. Sometimes the valve will be closed at idle even with the engine fully warmed up, but giving the throttle a good blip will open it because the shaft is offset, so as long as the shaft is free, high exhaust flow rate will open it.
I'd just wire it open with some aircraft stainless steel safety wire and leave it be. If you have the car judged just remove the wire and rewire it after the event... shouldn't even affect a PV.
DukeComment
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Re: Heat riser stuck closed
You may be right Duke, it is lots of trouble if some nuts are stuck.Big Tanks In the High Mountains of New MexicoComment
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Re: Heat riser stuck closed
Michael------
It's more than just the trouble of replacing it; it's BENEFICIAL to leave it wired open or eliminate it. I HIGHLY recommend leaving it wired open or completely eliminating it with a spacer. You'll notice little or any problem. Among other benefits, your right side muffler will be "immortal". Another benefit: no rattling.In Appreciation of John HinckleyComment
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Re: Heat riser stuck closed
Good point Joe. As it is now, after what looks like many years of the HR in place, the right muffler looks like it has twice the miles and time on it!Big Tanks In the High Mountains of New MexicoComment
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Re: Heat riser stuck closed
If you decide to go to the trouble of removing the heat riser and want an elegant solution: you can remove the butterfly from the shaft then reinsert the shaft and safety wire it with aviation wire from the inside. Appears perfectly stock, and the weight still moves on the shaft. Win-win DanComment
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Re: Heat riser stuck closed
During ops check/PV a judge should be at the back of the car and feel for exhaust pulses immediately after startup. The pulses should be very strong on the LH side and near nil on the RH side. If they are equal...
But it's easy to remove the wire for judging and rewire the valve open afterwards.
DukeComment
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Re: Heat riser stuck closed
A friend of mine had the same issue, he just didn't know it for a long time.
It was impossible to run the motor long without overheating.
He tried everything. Replaced almost everything.
In the end a stuck heat riser was identified when the exhaust manifold cracked.
After the valve replacement the car ran cool and had lots motor power.
RickComment
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