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Topic: Exhaust Flange Loosens

in Forum: C3 Fuel, Emission Control, and Exhaust Systems

Exhaust Flange Loosens

Posted: 8/5/23 12:42pm Message 1 of 10
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 72 coupe, 4 speed -  My drivers side exhaust flange keeps loosening up from the manifold. I can tighten the nuts, and in 10-15 miles, the leak can be heard again.

 Anybody have a fix for this ? Metal lock nuts, thread sealer, section of flex hose?

Could a bad motor mount be contributing to the issue, via extra vibration ? The mounts seem to be ok, but I have no idea how old they are.

 




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Re: Exhaust Flange Loosens

Posted: 8/5/23 2:19pm Message 2 of 10
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Overland Park, KS - USA
Joined: 7/9/2003
Posts: 914
Vette(s): 1973 Orange Metallic Coupe (orig owner), L82, 4 spd (WR), PS, (A/C & PW (I installed from wrecked 73)), leather, AM/FM Stereo, ran with '65 FI unit earlier & will again some day. 2023 Accelerate Yellow HTC Stingray

Do you have the donut gasket between the exhaust pipe and the exhaust manifold installed?




1973 L-82 4 spd

Re: Exhaust Flange Loosens

Posted: 8/5/23 2:46pm Message 3 of 10
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Yes, gasket is in place. It was fine for several weeks after new exhaust was installed, then gradually started developing a leak.

 After 3 re-tightenings, I think I need to put a new gasket in, because it doesn't go completely away any more. Maybe a new gasket will help. We shall see.

 It could be they didn't get the inside nut tightened all the way and the first leak got all this started. When I first discovered the leak, the inside nut was the loosest.



|UPDATED|8/5/2023 2:46:24 PM (AZT)|/UPDATED|



Re: Exhaust Flange Loosens

Posted: 8/5/23 4:29pm Message 4 of 10
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Overland Park, KS - USA
Joined: 7/9/2003
Posts: 914
Vette(s): 1973 Orange Metallic Coupe (orig owner), L82, 4 spd (WR), PS, (A/C & PW (I installed from wrecked 73)), leather, AM/FM Stereo, ran with '65 FI unit earlier & will again some day. 2023 Accelerate Yellow HTC Stingray

The gaskets I use appear to be made from a highly compressed asbestos or equivalent material with a steel sleeve on the inside of it. I always assumed that the gasket was to seal the gases in and that the steel sleeve was to protect the gasket from the heat. 




1973 L-82 4 spd

Re: Exhaust Flange Loosens

Posted: 8/6/23 4:37am Message 5 of 10
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Rock Hill, SC - USA
Joined: 8/2/2017
Posts: 59
Vette(s): 1977 White/Red

Is there any play in the nuts as they’re threaded on the studs? The diameter of the studs may have shrunk with corrosion over the years.  If so, you will need to replace the studs to get enough friction to keep the nuts tight. Not a fun job.




Re: Exhaust Flange Loosens

Posted: 8/6/23 10:57am Message 6 of 10
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The nuts don't seem to be loose around the stud, but I am going to replace them when I do the new gasket and see if that helps. Yeah, I would hate to have to pull the manifold off and try to get those studs out. That would probably be a winter job with lots of Kroil involved.

 




Re: Exhaust Flange Loosens

Posted: 8/6/23 5:12pm Message 7 of 10
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Grapevine, TX - USA
Joined: 8/26/2006
Posts: 1522
Vette(s): 1972 LT-1 convertible with factory air. 2017 Black Rose Grand Sport convertible.

Are you using metal lock nuts?




   

Re: Exhaust Flange Loosens

Posted: 8/6/23 6:52pm Message 8 of 10
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Equinunk, PA - USA
Joined: 10/31/2007
Posts: 2465
Vette(s): 1972 conv, 4-speed, 350, 200hp, numbers match, rally wheels, war bonnett yellow w/white top. good condition, nice driver.

Just a F.Y.I. on new nuts. Above all else, use BRASS nuts. They will not rust fast to the stud. Much easier to remove. 




Re: Exhaust Flange Loosens

Posted: 8/7/23 4:03pm Message 9 of 10
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F4Gary said:

Are you using metal lock nuts?

Not yet, I was told they could be very hard to get back off ?

  It may come to that, but I am going to try a new gasket and new nuts first.





Re: Exhaust Flange Loosens

Posted: 8/7/23 4:10pm Message 10 of 10
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manchestershark said:

Just a F.Y.I. on new nuts. Above all else, use BRASS nuts. They will not rust fast to the stud. Much easier to remove. 



I couldn't find any fine thread brass nuts locally, so I put a new donut gasket and new grade 8 nuts in today. And I was careful to get the donut centered and torqued consistently all the way around.

We shall see how this holds.

 If nothing else, it might get me to cold weather. Then I can pull the manifold, soak the studs in Kroil for a while, and put new ones in.




in Forum: C3 Fuel, Emission Control, and Exhaust Systems


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