Heat riser / exhaust leak
Thread Starter
Drifting
Joined: May 2012
Posts: 1,353
Likes: 44
From: Calgary Alberta
Heat riser / exhaust leak
Hello folks. Two questions for the educated:
1. What is the default position of a vacuum controlled heat riser valve on a stock 76?
2. I've got a good sized exhaust leak around my riser valve...used the old garden hose stethoscope trick to find it. How on earth does a guy go about sealing this up?
1. What is the default position of a vacuum controlled heat riser valve on a stock 76?
2. I've got a good sized exhaust leak around my riser valve...used the old garden hose stethoscope trick to find it. How on earth does a guy go about sealing this up?
Team Owner
Joined: Sep 2006
Posts: 31,283
Likes: 4,373
From: Westminster Maryland
Hi B,
I believe the heat riser's valve's weighted lever is up in the cold/closed condition and down in the hot/open condition.
Do you know if the extra internal sleeve is in place and that the sealing donut/gasket is in good shape?
Regards,
Alan
I believe the heat riser's valve's weighted lever is up in the cold/closed condition and down in the hot/open condition.
Do you know if the extra internal sleeve is in place and that the sealing donut/gasket is in good shape?
Regards,
Alan
Drifting
Joined: Apr 2007
Posts: 1,970
Likes: 45
From: Cameron Park CA
Burning Brakes
Joined: Oct 2008
Posts: 1,037
Likes: 14
From: Mobile Alabama
Hello folks. Two questions for the educated:
1. What is the default position of a vacuum controlled heat riser valve on a stock 76?
2. I've got a good sized exhaust leak around my riser valve...used the old garden hose stethoscope trick to find it. How on earth does a guy go about sealing this up?
1. What is the default position of a vacuum controlled heat riser valve on a stock 76?
2. I've got a good sized exhaust leak around my riser valve...used the old garden hose stethoscope trick to find it. How on earth does a guy go about sealing this up?
Team Owner
Joined: Sep 2006
Posts: 31,283
Likes: 4,373
From: Westminster Maryland
Hi,
I believe the heat riser was operated by a bi-metallic coil, (think choke coil), through at least the 72 model year cars.
I've also read that the exhaust flow from high rpm also contributes to opening the 'flapper' in the heat riser.
Regards,
Alan
I believe the heat riser was operated by a bi-metallic coil, (think choke coil), through at least the 72 model year cars.
I've also read that the exhaust flow from high rpm also contributes to opening the 'flapper' in the heat riser.
Regards,
Alan
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Burning Brakes
Joined: Oct 2008
Posts: 1,037
Likes: 14
From: Mobile Alabama
Thread Starter
Drifting
Joined: May 2012
Posts: 1,353
Likes: 44
From: Calgary Alberta
Hi guys...I also have a 70, and it has the "mechanical" coil style valve on it.
My 76 is the vacuum operated fella...and I think you're all correct about the default being open. This is good because I was worried it was stuck closed, but this can't be the case because vacuum would close the valve (rod would move up), etc. I feel good there.
My remaining problem is that I'm sure there's a leak where the intermediate pipe flange meets the bottom of the valve. Not sure how to repair this. Can't comment on the donut and the sleeve...haven't been in there yet. Perhaps these are the issue. It makes a very audible sputter at idle that gets quite loud under load.
My 76 is the vacuum operated fella...and I think you're all correct about the default being open. This is good because I was worried it was stuck closed, but this can't be the case because vacuum would close the valve (rod would move up), etc. I feel good there.
My remaining problem is that I'm sure there's a leak where the intermediate pipe flange meets the bottom of the valve. Not sure how to repair this. Can't comment on the donut and the sleeve...haven't been in there yet. Perhaps these are the issue. It makes a very audible sputter at idle that gets quite loud under load.
Drifting
Joined: Apr 2007
Posts: 1,970
Likes: 45
From: Cameron Park CA
Thread Starter
Drifting
Joined: May 2012
Posts: 1,353
Likes: 44
From: Calgary Alberta
Had this fixed the other day at a muffler shop just like you guys recommended...took them one hour and it was the riser and associated bolts. Sounds like a different car, oddly quiet really. Thanks for the help.