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Post Info TOPIC: Exhaust manifold gaskets yes or no?


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Exhaust manifold gaskets yes or no?


from the factory no gaskets but things mating surfaces are not as good as new



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What engine Kevin?



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1966 Strato Chief 2 door, 427 4 speed, 43,000 original miles


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Recently removed exhaust manifolds from a 1985 Pick-up Truck 350 that headers were going on in another application. I was surprised to find well fitting gaskets that were clearly original GM installation. First time I ever encountered this. Three small gaskets each side that fit perfectly around the exhaust ports.

This is what they looked like:

Image result for GM exhaust manifold gasket



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Ray White, Toronto ON

1973 LeMans 454 "Astro-Jet"

Built March 9, 1973 - Oshawa ON

 






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Ray, I have never seen factory small block exhaust manifold gaskets on a 350 in the 80's. GM lists nothing in the parts books and we've never seen any in our shop. Victor, FelPro, many companies make a gasket that looks like that for the small blocks but as far as I've ever seen, GM never offered an exhaust manifold gasket on small blocks until maybe the Vortecs at the earliest.

People often put them in because they have a gasket set for the engine that includes them so they think they are needed. Our experience has been that installing them just promotes manifold gasket leaks and manifold warping as soon as it starts to leak.

I wouldn't bet big tons of money on it but I'll bet those gaskets on that 85 were installed after the truck left the assembly line.

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1966 Strato Chief 2 door, 427 4 speed, 43,000 original miles


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4SPEED427 wrote:

What engine Kevin?


 327, it was suggested to me to use a high heat silicone 



-- Edited by 70 SS ACADIAN on Monday 16th of September 2019 01:30:58 AM

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Yes, good suggestion. No gasket, a nice thin layer of the high heat silicone in there and you should be fine. I assume the surfaces are pitted, that is the problem? You could get them shaved a tiny bit to fix that. I am thinking they are numbers matching pieces, so you want/need to use those exact ones?

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1966 Strato Chief 2 door, 427 4 speed, 43,000 original miles


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The only small block Chev exhaust manifold gaskets I ever seen listed as service parts from GM were the 55-56 265 V8. 



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I am having a very hard time grasping how two flat surfaces mated together with no gasket at all could work in keeping silence. I have always used the high heat special gaskets for stock exhaust manifolds and never had any issues at all. Headers on the other hand are a beast at blowing out header gaskets. 



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1957 Pontiac Pathfinder Deluxe sedan restored 261 six

1974 Chevrolet Caprice Estate wagon low milage original 400 V-8



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I have never run an exhaust manifold gasket on any small or big block I've ever owned and don't ever recall having a leaky manifold. Lots of other manufacturers don't seem to have the knack of sealing them but GM certainly figured it out, whatever they did.

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1966 Strato Chief 2 door, 427 4 speed, 43,000 original miles


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For fun I just checked on the GM parts computer and the first small block I find one listed for is the 96 Vortec. Of course it doesn't go back to the days of the 265 but it does cover the 350's for decades.

And as always, I'll stand corrected if someone comes up with a GM part number for such a part for a small block in the 60's to 90's era pre Vortec.

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1966 Strato Chief 2 door, 427 4 speed, 43,000 original miles


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While I never have used gaskets and prescribe to this way of thinking as did GM, on reflection we assumed the 85 engine was untampered with however the exhaust manifolds had no AIR ports and it was a dual exhaust conversion so perhaps these were added after factory assembly after all, just been on the engine for 30 years or so.



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Ray White, Toronto ON

1973 LeMans 454 "Astro-Jet"

Built March 9, 1973 - Oshawa ON

 






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73SC wrote:

Recently removed exhaust manifolds from a 1985 Pick-up Truck 350 that headers were going on in another application. I was surprised to find well fitting gaskets that were clearly original GM installation. First time I ever encountered this. Three small gaskets each side that fit perfectly around the exhaust ports.

This is what they looked like:

Image result for GM exhaust manifold gasket


 GM Part# 3711675 - Field Fix only as far as I know never factory installed - sold a ton of them back in the day.



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I'm not sure all 350's in that era would have had AIR though Ray. It's quite possible the manifolds had no ports in them on that vehicle from day one.

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1966 Strato Chief 2 door, 427 4 speed, 43,000 original miles


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I do not doubt anyone here but i still can not grasp how there would not be noisy exhaust leaks with no gasket. I am at a total loss how that is possible. I remember back in 1986 taking my 57 283 out of my 57 Chev and seeing those special gaskets there when i pulled the manifolds off. In my many years in the hobby and working on vintage engines, i have never run into exhaust manifolds with no gaskets. 235's, 261's 283,s, 307,s 350,s 400,s, 250,s. All the motors i worked on had exhaust manifold gaskets. Cheers.



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1957 Pontiac Pathfinder Deluxe sedan restored 261 six

1974 Chevrolet Caprice Estate wagon low milage original 400 V-8



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I can't see someone on the line holding three gaskets in place and slamming on the manifold.

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CDN2PLS2 wrote:

I can't see someone on the line holding three gaskets in place and slamming on the manifold.


 Auto manufacturing giants have a way of making the impossible very possible when it comes to getting things done in a very speedy manner. 



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1957 Pontiac Pathfinder Deluxe sedan restored 261 six

1974 Chevrolet Caprice Estate wagon low milage original 400 V-8



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Now that we have that cleared up I guess I just have to figure what side gets gaskets and what side gets no gaskets lol



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A Poncho Legend!

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Has the jury reached a verdict?

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1966 Strato Chief 2 door, 427 4 speed, 43,000 original miles


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For what it's worth Kevin, even though I pretty much guessed the outcome, I just went to the garage and looked at an extremely virgin appearing 1966 283 that I pulled from my Strato Chief. All the stock bolts, washers, locking hardware etc in place on the exhaust manifolds. I seriously doubt those bolts have been touched since 1966.



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1966 Strato Chief 2 door, 427 4 speed, 43,000 original miles


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gona go with out, use the silicone. I can always put gaskets in after if I have trouble. in the past I have to say I did use gaskets



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But did you need to, or did you use them because they were in the kit so you thought you should?

If you have to put them in later, slot the holes and you don't even have to remove the bolts.

Do you not have someone who can shave them for you?

Before I install mine I always take a long rigid sanding block and run it over the face until everything is clean.

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1966 Strato Chief 2 door, 427 4 speed, 43,000 original miles


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buddy`s engine builder does have a belt sander table set up to do that



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That would be perfect as long as it's a long enough true surface.



-- Edited by 4SPEED427 on Monday 16th of September 2019 09:01:57 PM

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1966 Strato Chief 2 door, 427 4 speed, 43,000 original miles


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really think you could go either way so no wrong answers here. Thanx for all the input guys



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