Leaking exhaustmanifolds.

by Hs1973 Tue May 09, 2017 11:38 am

Hi guys.
Here we go again, im running original fast iron manifolds. And one is leaking at the head and where it meets the exhaust under the passenger side feet area, im going to take them both of and resurface them. But has anyone any advise on what to do at the bottom where it meets the exhaust. There is no gasket there, do i keep it that Way, also what is the best gaskets to use between the heads and manifolds? I dont want any more leaks for some time. I hate the sound of it and i rather not drive it until its fixed. Any and all advise is welcome.
Regards Henrik.

by bigredlaguna Tue May 09, 2017 10:14 pm

Normally, the iron head/manifold doesn't need gaskets due to both surfaces being machined and the expansion rate being the same. I guess the only other thing you can do is check the flatness of the mating surface of the exhaust ports. I wouldn't worry about gaskets unless the head is not true.

You might be able to see where the leak was at due to carbon tracking. I would remove any carbon traces from the head, and check those areas first for straightness.

I really only have experience with header gaskets, but I suppose they would work well for cast manifolds also. I have had very good luck with the Mr. Gasket ultra seal gaskets on header applications and would recommend them.

These are what I recommend
https://www.summitracing.com/parts/mrg-5907/overview/make/chevrolet

by S3SS Wed May 10, 2017 6:23 am

Passenger side manifold to pipe, if you find the spacer block (cast also) it requires a donut to seal where pipe meets. Spacer block is used with EFE delete.

by Hs1973 Wed May 10, 2017 10:00 am

I have heard about the manifolds not having a gasket from the start, bit i have never seen a V8 engine without gaskets at the heads. I have read about cobber gaskets, but that is for headders i Think? I was just wondering if there was a better choice in gaskets than the usual silver ones i usually get.
I have always wondered why the driverside has a donut seal and the passenger side is without. Is it because there used to be a heat deal thing with a flap that would be closed when cold. I Think my elcamino had one, and it would rattle like crazy until i yanked it out. Anyways if there is a leak there because its old, can i use a exhaust cement type deal where the manifold meets exhaust. Or has anyone Found a better Way.
Im going to try and resurface the lover joint as the upper part. But i would like some ekstra insurance from leaks, cause i have a hard time understanding that it should not have some sort of gasket there.

by bigredlaguna Wed May 10, 2017 4:02 pm

The theory is that two parts with perfectly flat surfaces, made of the same material, does not need a gasket. The expansion rates are equal as the temperature changes.

by Hs1973 Thu May 11, 2017 9:30 am

I am sure it would work if all parts have fresh machines surfaces, but my old manifolds are not that fresh. Im going to take it apart this weekend and resurface the manifold flange and put fresh gaskets in it. I Might give exhaust cement a try at the bottom joint. It can not be worse than now. Its not that it is a massive leak i have. But it is enough to hear the compression stroke when i ride past a fence or guardrail, at first i thought it was a Stone hat was caught in my tire. But then i realised it was exhaust leak. And now i cant ignore it, it makes my car sound less than healthy more like a old ratrod actually, cant have that.

by crice63 Fri May 12, 2017 12:58 am

After I changed my engine but before I got my headers I was running the old exhaust manifolds with no trouble or leaks. We just welded the valve open on the heat riser, and I'm pretty sure there was a donut on the passenger side just like the driver side. In fact I painted the manifold and put on new donuts for a good seal on the old exhaust.

by rosco77 Tue May 16, 2017 9:26 pm

My Dad told me of a fix he did on a 1969 Cutlass that was leaking where the pipe met the manifold on the passenger side. It had the same type of donut fitting the driver side had, on yours should be on the bottom of the flap. Anyhow, he cut the bottom off of a soda can, cut the center of it out, and it was a perfect fit. Sealed it up good and never leaked again.

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