1969 427/400 Exhaust Manifold Resurfacing

[Ned T.]

How much of a gap does it take before you justify having the exhaust manifolds resurfaced? I set mine on a heavy steel table I have and just have a variance of the thickness of a sheet of paper at most. Is this enough to cause a leak after they're tightened down? Could I get by with Permatex copper high heat sealer or should I get them resurfaced? This is the first time I've ever put exhaust manifolds on without a gasket.....I might have to hide them from myself...it's so tempting! If I put them in that spot where I put everything " so I'll know where it is" I'll be sure to never see them again.

[Dick W.]

Re: 1969 427/400 Exhaust Manifold Resurfacing

Use the copper Permatex and not worry about it. You can run the car at high idle for about 15 minutes, shut the engine down and retorque the manifolds

[Jim R.]

Re: 1969 427/400 Exhaust Manifold Resurfacing

Wondering why copper permatex and not just black rtv silicone ?

[Joe L.]

Re: 1969 427/400 Exhaust Manifold Resurfacing

Wondering why copper permatex and not just black rtv silicone ?

Jim------


UltraCopper has the highest heat resistance of any of the Permatex RTV's. However, it's rated to a maximum of 600 degrees F. I think that's marginal for an exhaust manifold at the interface with the cylinder head.

[Jim R.]

Re: 1969 427/400 Exhaust Manifold Resurfacing

Thanks Joe. Jim

[Dick W.]

Re: 1969 427/400 Exhaust Manifold Resurfacing

Jim------


UltraCopper has the highest heat resistance of any of the Permatex RTV's. However, it's rated to a maximum of 600 degrees F. I think that's marginal for an exhaust manifold at the interface with the cylinder head.

Joe, I used it to seal header gaskets on the 454 dually that I pulled the parts trailer with. Before using it, a set of gaskets would last 1,500 miles, tops. After is used it there was over 10k on the gaskets when it was stolen. Unless he is towing, I think that he would probably not see much more than 600 degrees, if he ever saw that.

[Joe L.]

Re: 1969 427/400 Exhaust Manifold Resurfacing

Another option (but not for those who demand 100% correctness): later GM 8.1L big blocks used an MLS (multi layer steel) gasket between the manifolds and the heads. These gaskets will work on earlier Mark IV big blocks if a few locating tabs are trimmed off. I like these (especially for aluminum head applications). The GM part number is 12558275. Use great caution when installing these; the edges of the layers are as sharp as razor blades.

[Ned T.]

Re: 1969 427/400 Exhaust Manifold Resurfacing

I just bought the Permatex Copper and it now has a 700 degree rating. At least that's what it says on the package. I'll be installing the manifilds today. I will use the 1/8" bead and let it "skin over" before installing like I read in one of Dick Whittington's earlier posts.

Thanks, Ned

[Philip A.]

Re: 1969 427/400 Exhaust Manifold Resurfacing

How much of a gap does it take before you justify having the exhaust manifolds resurfaced? I set mine on a heavy steel table I have and just have a variance of the thickness of a sheet of paper at most. Is this enough to cause a leak after they're tightened down? Could I get by with Permatex copper high heat sealer or should I get them resurfaced? This is the first time I've ever put exhaust manifolds on without a gasket.....I might have to hide them from myself...it's so tempting! If I put them in that spot where I put everything " so I'll know where it is" I'll be sure to never see them again.

Is it possible that the gap will close with heat expansion?

[Ned T.]

Re: 1969 427/400 Exhaust Manifold Resurfacing

Phillip,

I will retorque the bolts after the engine is warmed up. I only have the engine sitting in the chassis so I have great access to the manifold bolts.