Exhaust Manifold Leaking - A Bit

[Kirk M.]

For those who don't know, I just replaced both heads on my 67 327/300hp vette a few weeks ago. We initially installed exhaust manifold gaskets even though they are not NCRS correct. I took the DS set off two nights ago and now have a small leak that I can hear from the center portion of the manifold. It sounds a little bit like a loose rocker arm, but much softer and only audible from the DS of the car. When I had a loose rocker arm, you could hear the clatter from both sides of the engine. I must say that the manifold leak stops making any sound at all after a minute or two of engine warming. I am assuming the metal heats up and expands sealing the leak. Anyway, now I am torn about whether I should take the other side off (have AC so it is a bit more of a pain), or replace the gaskets (take the deduct) and not having a temporary leakage in my DS exhaust manifold.

What is your vote?

Kirk

[Dick W.]

Re: Exhaust Manifold Leaking - A Bit

Permatex Copper silicone is the trick to seal leaking exhaust manifolds. Just a thin bead around the exhaust port, not enough to squish out, and your leaks are fixed.

[Mike M.]

Re: Exhaust Manifold Leaking - A Bit

when rebuilding an engine, or anytime i have the exhaust manifolds removed, i take them to the local machine shop and have them surfaced to remove the concavity or convexity.mike

[Bill I.]

Re: Exhaust Manifold Leaking - A Bit

Dick, describe a 'thin' bead. Let's use a pencil as a guide, bead the size of pencil lead, maybe 1/8", or size of the pencil little over 1/4". Thanks, Bill.

[Dick W.]

Re: Exhaust Manifold Leaking - A Bit

Dick, describe a 'thin' bead. Let's use a pencil as a guide, bead the size of pencil lead, maybe 1/8", or size of the pencil little over 1/4". Thanks, Bill.

1/8" would be plenty. Let the silicone "skin" over before assembling it and you are good to go.

[Patrick H.]

Re: Exhaust Manifold Leaking - A Bit

when rebuilding an engine, or anytime i have the exhaust manifolds removed, i take them to the local machine shop and have them surfaced to remove the concavity or convexity.mike

Agreed.
I'd only think about the Permatex if you've already had them surfaced and then still have the leak.

I think the leak will go away with surfacing.

[Dick W.]

Re: Exhaust Manifold Leaking - A Bit

Patrick, I have never had one leak after using the Permatex. I even works well with tube headers, which are notorious about leaking gaskets.

[Timothy B.]

Re: Exhaust Manifold Leaking - A Bit

Dick,

I never thought any material would stand up to the exhaust heat and pressure. Sounds like a good idea and cheep insurance if it works..

[Dick W.]

Re: Exhaust Manifold Leaking - A Bit

Dick,

I never thought any material would stand up to the exhaust heat and pressure. Sounds like a good idea and cheep insurance if it works..

I started using it almost 25 years ago. I had a Chevrolet Dually 454 that I pulled my parts trailer with. I got a wild hair and installed a set of headers. About every 4-5k miles I would be replacing the gasket on one side or the other. I was at Bloomington and had blown a gasket. I was in the motel parking lot changing it and someone, who I do not remember the name, came up and suggested that I try the Permatex. I had the truck another 20k miles before it was stolen, and never had to replace a header gasket. I use it on everything exhaust

[Kirk M.]

Re: Exhaust Manifold Leaking - A Bit

Did the copper High Temp Permatex last night to the DS. PS still has gaskets on it. Did it last night. Might give it a shot tonight and see if the leak is gone. Will let you know cause I hate it when people don't follow up on their questions/problems. If all goes well, I will remove the gaskets from the PS and do the same.

Kirk

[Joe C.]

Re: Exhaust Manifold Leaking - A Bit

Patrick, I have never had one leak after using the Permatex. I even works well with tube headers, which are notorious about leaking gaskets.

Dick,

Did you ever try sealing tube headers (assuming everything is flat) with high temp silicone and no gaskets. Torque the bolts to about 25 ft-lbs and forget them. Eliminate problem of gasket creep and constantly re-torquing flange bolts with the thick gaskets.

[Dick W.]

Re: Exhaust Manifold Leaking - A Bit

Dick,

Did you ever try sealing tube headers (assuming everything is flat) with high temp silicone and no gaskets. Torque the bolts to about 25 ft-lbs and forget them. Eliminate problem of gasket creep and constantly re-torquing flange bolts with the thick gaskets.

When I cut the flanges it helped a little, but when I went to the silicone problem solved. Never thought that silicone alone would work. Tube headers are not exactly an example of perfect machining in the port area