Rick Hodgkins

Built a 400 recently and put new manifolds on.
I hear a leak now when its cold.
Are metal exhaust gaskets available and a better option?
Or should I just skip them?
They will get planed when they come off this time.
I don't want to do this twice tho...

Olds64

Did you have the exhaust manifold mating surface on the head machined? If not definitely use gaskets.

joe_padavano

While I'm a fan of doing it the factory way (no gaskets), the reality is that half-century old manifolds can be warped, and even surfacing them doesn't always work. If you do need gaskets, I strongly recommend Remflex. Just pay attention to the bolt torque. If you squash those gaskets, you will damage them.

Run to Rund

An alternative is copper gaskets such as Summit offers. I find it too easy for the Remflex to get squashed when trying to tighten the bolts so they don't vibrate out. Either way, I recommend surfacing the manifolds and the heads.

Rick Hodgkins

Thanks for the info
So the manifolds were new when installed in the spring, used the gaskets in the build set.
The heads were not machined on the port side I believe.
When they come off I will have them cut, good advice on torque and copper.
Been fine all summer, and once hot they are tight and not leaking.
Just scratching my head how these left Lansing and ran for thousands of miles with no issues, yet here I am doing it again.
Gonna wait till winter at this point, not gonna take it down yet.
Just frustrating, but nothing new with this car lol

OLDSter Ralph

When the cars left the factory, they were flat and new. Several thousand heating and cooling cycles will change the shape of machined and cast parts. These heating and cooling cycles from normal driving relieve stresses in parts and cause them to change shape. The parts usually stabilize after the stresses are relieved. Light resurfacing the mating surfaces should last another 50 years.
If you machine the exhaust port side of the head flat, you may want to check and resurface the exhaust manifolds also. Oh, and your exhaust manifolds were new in the spring ? Things are only "new" once.
Using gaskets is not a sin.

1970greensupreme

I think coat of extreme temp gasket maker should do the trick

Rick Hodgkins

Well I guess my quandary is based on not wanting to do this again especially in the short term.
The build kit was Felpro which bothers me to know that quality has failed.
I didn't know they left the factory metal to metal and leaks is why I went with original manifolds vs headers due to nagging leaks headers tend to be famous for.
1970GS: Are you saying high temp sealer metal to metal or coating the new gasket with it.
I suspect heat crush has opened things up for the blow out somewhere and without a gasket never gonna happen again.
Kinda leaning towards cutting the manifolds to true up the mating surface and going without gaskets tbh.
Couple of guys in the know have said chances of the head surface being bad is pretty rare, and even the manifold being new not very common to be warped in this short period.
I am listening to all experiences with this, because I just don't know or know what to do so this is put to bed once and for all.

OLDSter Ralph

1. Have you re-torqued all of the exhaust manifold bolts ?
2. What are you trying to do ? Gaskets ? No gaskets ?
3. I think header leaks are exaggerated. Loose bolts and restrictive exhaust systems are the usual culprits. Re-torqueing headers and gaskets would likely solve leaks.
4. Exhaust manifold surfaces can be warped. Not sure what "couple guys in the know" are calling "bad". More than .002" ? More than .020" ?
I think you might be "over thinking" this. Use gaskets, some sealer and re-torque the bolts in proper sequence after you have run the engine through some heating/cooling cycles. This pertains to common gaskets, NOT Remflex.
.....Just my two cents worth.

Rick Hodgkins

I have retorqued to 30 inside to ends, but its probably too late imho None were loose as it happens
I have no prefs gask or no gask, just don't want to do this again.
Header leaks may be exaggerated, but I have heard them on other cars.
Lead and I will follow, my local guys are a 30 year engine machinist and the son of a pro stock/speed shop owner both of which I trust completely for guidance.
Its hard for me to know when advice here is split on Remflex if you know what I mean.
I just don't want to do this again is all.
Thanks for the assist on this

OLDSter Ralph

I am really not clear what "this" is that you don't want to do again. I purposely excluded Remflex from my suggestion because I have never used it. Joe P. uses it and is impressed with it, and I am sure he has good reasons.

"my local guys are a 30 year engine machinist and the son of a pro stock/speed shop owner both of which I trust completely for guidance." What is the purpose of this opinion poll (thread), if you trust them completely ?

Rick Hodgkins

I don't want to have to take the manifolds off again

matt69olds

Unless the head or manifolds are warped bad enough to “wave” at you, I don’t see how the proper gaskets could leak. You don’t need any sealers for the gaskets, install them dry and torque them.

Make sure the gaskets fit the manifolds, the small block exhaust manifold gaskets look similar but don’t match up to the bigger manifold ports.

I use a bead of high temp exhaust RTV around the header gasket port before sliding them into position. Let the RTV set up a little, then tighten. After s couple heat cycles, retorque the bolts. As long as the header has a decent flange, you don’t overtorque the bolts, and are using decent quality gaskets, you shouldn’t have leaks.

oldsmoboogie

I use Remflex gasket’s. They work very well and are not that expensive. I wont use anything else.

rogue_ryder

Remflex for the win! Seriously the best you can get and they won't leak. High Temp Copper RTV will also work and is cheaper. I've used both and prefer the Remflex as it's faster, easier and cleaner. Both methods are leak free whereas those metal gaskets like the Fel Pro ones I've had leak on me with headers anyway (might work on iron manifolds).