Exhaust conection, Manifold to pipe

[Antonnick]

I have had to replace the broken gasket between the manifold and the exhaust pipe flanges with a new one. They are connected using brass nuts ( why brass??) which I have new. However, it still is blowing and I do not seem to be able to do the nuts up tight enough to stop it. Also I am worried that by overtightening the brass, the threads will break.

Is there a trick I am missing?

[glang]

Hi, I believe brass is used to prevent the nuts seizing on the studs as if they were of a ferrous metal the heat plus corrosion would make them very difficult to remove.

The downside is that you cant torque them up nearly so much so its very important the two flanges line up perfectly. Even though the copper gasket is quite thick if there is misalignment, for example from using a poorly made pattern exhaust, then the joint will never seal.

Can you see any misalignment? If so you could try releasing the exhaust mountings and moving it around until the flanges bolt up better then adjusting the mountings as required....

[Antonnick]

Copper? The Gasket looks like Alu to me. Perhaps it is a sandwich construction.

I can check for any misalignment later in the week - I am away for a few days.

[RobPearce]

The original gaskets back in the day were a copper/asbestos sandwich. Those available now are a variety of constructions, but some still have a copper outer skin.

One of the common problems with the downpipe flange gasket is that, when you dismantle it because it's blowing, there is all sorts of crud left behind, and the surfaces aren't that easy to clean up, or even to see. If they're not properly clean, it won't seal.

[Bitumen Boy]

Mine kept on blowing at this point for years, over and over again. Eventually I realised that there was too much movement in the joint as the standard support clamp that mounts to one of the bellhousing bolts wasn't really up to the job. 

 

I cured it in the end by taking a piece of thick steel plate with an angle along one side - ex garage door mechanism - and using it to support a standard U bolt type clamp to the exhaust while solidly mounted to two (or maybe 3, not looked in a while) of the bellhousing bolts. It's never given trouble since, there's nothing more satisfying than sorting out these niggling repetetive faults.

[Jonny-Jimbo]

One issue I've seen in the past with this join is that the old manifolds can fracture quite badly, particularly if they are over-tightened. This can lead to the exhaust blowing through the cracks, and people think it's the join but it's not.

As a result they slather the join in exhaust paste etc, but still miss the cracks.

As has been pointed out too, sometimes the mating faces just aren't cleaned enough.

Brass is used to stop the nuts seizing on, and you can get extra thick brass nuts, giving more thread contact, so you can tighten them up more.