Hello Oldsmopeople. I’m finishing a restoration of a 1970 442 convertible. It’s a frame off and everything is new or restored. I’ve installed my Gardner exhaust but I’m getting leaks where the pipes bolt up to the exhaust manifolds. I know there is no donut gasket, and the pipes have a conical flange that has to seat just right. I loosened them, then loosened the back of the pipe at the muffler, then tried to seat the pipes, but I still get leaks. Should I use a high temp sealant? thanks for any advice.

Steve

 

I've used this stuff since working at Midas back in the 80's as a kid.

 

Muffler cement which tends to crack will work. Optimum Grey is a high temp RTV, very thick, durable and nearly invisible.

 

Ok, so it sounds like everyone is recommending a high temp sealant. Should I stop trying to make it seat without sealant? We’re they sealed originally?

 

No. You could try emery cloth first if there is any corrosion or pitting. If still no, choose your sealant.

 

I usually leave the pipe with the flange loose where it connects to the muffler or other pipe, so that it can pivot. The angle that the conical flange sits on the exhaust manifold is critical to the proper sealing. Also another issue can be rust on the threads on the stud in the manifold, preventing the nuts from screwing in far enough to tightening the flange against the front pipe conical flange.

 

^^^THIS. Usually the manifolds need to be cleaned up a little. If that isn't the problem, use Walker Acousti/Seal. This stuff is magic for sealing exhaust leaks. It isn't "muffler cement", it's a black sealant that remains pliable.

 

Thanks, Joe.

 

I have the same issue on my 68 442, 400 engine. Exhaust has been installed for approx 30 yrs. I don't see any perforations on the head pipes, and the rest of the exhaust system is still solid. Aluminized steel pipes, not SS. But I do have developed leaks on both sides, at head pipe to exhaust manifold. The Assembly Manual shows no donut ring flange gasket at this joint on 68's also, can someone please confirm? I haven't pulled the connections open yet, so just wondering.
Assuming the head pipe flares/ends are still in good shape, I should focus attention on the manifold mating surfaces, alignment, new threaded fasteners, and the Acousti Seal compound Joe recommended. Anything else?

Thanks.

 

The stock manifolds have integral metal sealing surfaces. You couldn't use a donut if you wanted to.