Exhaust Manifold Leak
Thread Starter
Instructor
Joined: Mar 2020
Posts: 167
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From: Virginia
Exhaust Manifold Leak
I have a 78 Corvette with a 400 small block. The exhaust manifolds that are on it look like the stock ones for the corvette and I think they are leaking. I wanted to pop them off and put new gaskets on there. As I am reading, I have seen a couple videos where the person says to use "ultra copper max temp RTV" and not to use a gasket. They said that out of the factory they didn't use gaskets on the stock exhaust manifold and if you do use a gasket it will just blow out. So which should I use? My next hurdle is because I don't have the original engine I don't know exactly how to find the right parts. On the back side of the engine it has GM 6951509 stamped onto it, from what I understand most of the parts that would fit my original L48 should fit this engine because the outside of the engines where the same. My exhaust manifolds I believe are the original for the corvette or the truck the engine came from, GM 3932461 RH 17. What do you guys recommend, and if I use a gasket which should I use?
Pro
Joined: Feb 2013
Posts: 572
Likes: 61
The factory didn't use gaskets but the machined surfaces were flat when they were manufactured. With time and the age of these engines the surfaces are not perfect and there tends to be leaks If you install gaskets they are not going to blow out any more than they would on any other engine that has them. .
Thread Starter
Instructor
Joined: Mar 2020
Posts: 167
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From: Virginia
Dr. Detroit
Joined: Mar 2012
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From: New Braunfels Texas
Thread Starter
Instructor
Joined: Mar 2020
Posts: 167
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From: Virginia
Question about my torque specs for the bolts, what should they be? I think my assembly manual says for the outer bolts to be 24-30 n/m and inner bolts to be 34-40 n/m but my cylinder heads are aluminum and think it needs to be lower?
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Well, have no idea what NMeters means in foot pounds
I have never used a torque wrench on exhaust manifolds. Get them good and tight!
I have never used a torque wrench on exhaust manifolds. Get them good and tight!
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Dr. Detroit
Joined: Mar 2012
Posts: 10,097
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From: New Braunfels Texas
I have never used a torque wrench on intake or exhaust bolts......if you think you are tightening them too tight....you probably are.
One thing I do use is a short 3/8" ratchet......will keep you from not knowing your own strength......a great addition to anyone's tool arsenal.
https://www.mcmaster.com/53035A21/
Bottom line is to snug them up.....use lock washers.....the mentioned anti-seize is good practice....it will keep the steel bolts from galling out the aluminum threads.
Don't overthink it......tighten snug....let the lock washers do their job.....you have nothing to gain by overtightening a manifold bolt.
Jebby
One thing I do use is a short 3/8" ratchet......will keep you from not knowing your own strength......a great addition to anyone's tool arsenal.
https://www.mcmaster.com/53035A21/
Bottom line is to snug them up.....use lock washers.....the mentioned anti-seize is good practice....it will keep the steel bolts from galling out the aluminum threads.
Don't overthink it......tighten snug....let the lock washers do their job.....you have nothing to gain by overtightening a manifold bolt.
Jebby
