Exhaust Donut
Thread Starter
Instructor
Joined: Dec 2020
Posts: 126
Likes: 27
From: Mesa, AZ
Exhaust Donut
Got two questions for you guys regarding the exhaust gasket and donut on my 74 L48. I noticed an exhaust leak yesterday on the passenger side where the heat riser meets the pipe. Got the nuts off the studs fine, unbolted everything, and dropped the entire pipe. Found no gasket between the heat riser and manifold. I assume there should be one there? Noticed two different gaskets available too. One is for a 3 1/16" bolt hole center and another is for a 2 11/16" center. The 3 1/16" looks correct but I can take it to parts store to verify.
There is a donut between the pipe and heat riser. The donut is not soft but does not appear to be steel however as it is flaking off a lot. According to the factory AIM, there should be a donut sleeve that goes inside the exhaust pipe and the donut seals between there and the heat riser. I do not have that donut sleeve. I've read around the forums and there are a few posts stating if a steel donut is used, the sleeve isn't necessary. Is this correct or should I be ordering the sleeve? Thanks!
There is a donut between the pipe and heat riser. The donut is not soft but does not appear to be steel however as it is flaking off a lot. According to the factory AIM, there should be a donut sleeve that goes inside the exhaust pipe and the donut seals between there and the heat riser. I do not have that donut sleeve. I've read around the forums and there are a few posts stating if a steel donut is used, the sleeve isn't necessary. Is this correct or should I be ordering the sleeve? Thanks!
Le Mans Master
Joined: Jan 2001
Posts: 6,741
Likes: 1,383
Follow this link. It explains why you want to have the sleeve and has drawings and whatnot. https://www.corvetteforum.com/forums...ust-donut.html
ah... here's the reason per Willcox. You wanna have it: https://www.corvetteforum.com/forums...post1598267224
ah... here's the reason per Willcox. You wanna have it: https://www.corvetteforum.com/forums...post1598267224
Got two questions for you guys regarding the exhaust gasket and donut on my 74 L48. I noticed an exhaust leak yesterday on the passenger side where the heat riser meets the pipe. Got the nuts off the studs fine, unbolted everything, and dropped the entire pipe. Found no gasket between the heat riser and manifold. I assume there should be one there? Noticed two different gaskets available too. One is for a 3 1/16" bolt hole center and another is for a 2 11/16" center. The 3 1/16" looks correct but I can take it to parts store to verify.
There is a donut between the pipe and heat riser. The donut is not soft but does not appear to be steel however as it is flaking off a lot. According to the factory AIM, there should be a donut sleeve that goes inside the exhaust pipe and the donut seals between there and the heat riser. I do not have that donut sleeve. I've read around the forums and there are a few posts stating if a steel donut is used, the sleeve isn't necessary. Is this correct or should I be ordering the sleeve? Thanks!
There is a donut between the pipe and heat riser. The donut is not soft but does not appear to be steel however as it is flaking off a lot. According to the factory AIM, there should be a donut sleeve that goes inside the exhaust pipe and the donut seals between there and the heat riser. I do not have that donut sleeve. I've read around the forums and there are a few posts stating if a steel donut is used, the sleeve isn't necessary. Is this correct or should I be ordering the sleeve? Thanks!
Last edited by carriljc; Mar 4, 2021 at 10:05 PM.
Thread Starter
Instructor
Joined: Dec 2020
Posts: 126
Likes: 27
From: Mesa, AZ
Follow this link. It explains why you want to have the sleeve and has drawings and whatnot. https://www.corvetteforum.com/forums...ust-donut.html
ah... here's the reason per Willcox. You wanna have it: https://www.corvetteforum.com/forums...post1598267224
ah... here's the reason per Willcox. You wanna have it: https://www.corvetteforum.com/forums...post1598267224
If the metal sleeve protects the packing on a 'soft' donut, am I incorrect in thinking I do not need the sleeve when using an all metal donut? Not trying to skimp anywhere, just genuinely curious if it's needed in my application.
1967 Pedal Car Champion
Joined: Mar 2020
Posts: 9,135
Likes: 4,244
From: US-PNW
Use the sleeves no matter the donut material. They help create a seal by aligning everything and channeling exhaust gases. You might be able to find the properly sized pipe connector (sleeve) at OReilly's -- I believe I've seen them there for much less $ than the Corvette parts vendors. By also installing the triangular gasket between the riser and manifold it'll help seal the system. Just make sure the heat-riser valve (if your riser block has it) is functional after everything is buttoned back up.
Le Mans Master
Joined: Aug 2005
Posts: 6,539
Likes: 1,972
From: Temple Terrace Florida
Call your local muffler shop. They have the equipment to make up the sleeve while you wait. You can also get the donut at any well equipped parts shop like NAPA. The muffler shop should have a donut as well. Jerry
Le Mans Master
Joined: May 2007
Posts: 5,025
Likes: 1,120
From: North tonawanda NY
When I bought my 74 the original donuts were also also completely toast and the pipes were very loose as a result. I was not so lucky and snapped frozen bolt when trying to tighten despite the threads not being bottomed out. I ended up swapping to sidepipes in my situation which I wanted to do anyway. I could not believe the PO drove it that way.
Last edited by augiedoggy; Mar 5, 2021 at 10:05 AM.
