I spent today installing a new catalytic converter I bought from FCP Groton for my '86 240 sedan and it was a good fit. I had had a crack in my header/down pipe so I pulled one from a low mileage donor car and installed new OEM Volvo gaskets for both. I started everything up and my car sounded like a rusty old red-neck truck without a muffler. I traced the exhaust leak to where the top of the header/down pipe bolted up to the exhaust manifold. I can feel the air where the two meet. It's like I don't even have a gasket in there at all. The connection between the front of the the cat where it meets the end of the down pipe has a nice quiet and air free seal. What did I do wrong? I removed the header/down pipe to check it for rough surfaces as with the exhaust manifold surface and both were smooth and fine. Any suggestions???
I made sure that my support brackets were not causing any flex or stress on the header/down pipe.

Thanks in advance for your thoughts on my problem.

I have an '86 - 740 with a similar problem. I have had the same leak you're talking about for the past year and a half or so... I can tighten the bolts down so the leak disappears but with the expansion and contraction it loosens right up in a couple of weeks time and I go from smooth sounding to rumbling. Let me know if you find something that works for you.

First, I would follow Aye Roll's suggestions. Maybe you can seal it up or at least reduce the size of the leak. Then you might consider trying Fire Seal 2000. It's designed specifically for manifolds and other exhaust parts. It's a high temperature sealant made by the POR-15 people. Worked great to seal 2 small holes in my header pipe. If you are interested, check it out on the POR-15 website.

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90 244DL about 1/4 million miles - original engine/drivetrain :)

Sometimes I have to use 2 gaskets and lots of RED high temp silicone to not sound like the Spruce Goose looking to land.
buena suerte,
el Raidman

Then why didn't the original gasket have any sealing compound on it? It just fell right off when I seperated the pipe from the manifold contact point.

XrayBob.

You shouldn't need any, and there really isn't any sealer that's sufficient in the face of 1000°F + exhaust temperatures. If you simply cannot get the manifold to bolt to the headpipe flange correctly, then there are a few possibilities-
the headpipe flange is bent, not flat, can't seal. Ought to be obvious looking at the top of it.
The headpipe itself is bent, not formed right. Possibly due to an accident, or being lifted with a forklift in the junkyard. Maybe you can straighten it, or unbolt it from the cat, bolt it onto the manifold and THEN onto the cat.
The headpipe mounting bracket at the bell housing is interfering. I leave this thing off, because it's usually a royal pain.

I also always replace the nuts with the correct copper washer-face nuts from FCP Groton. They're 16mm just for reference.
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Rob Bareiss, New London CT ::: Roterande Fläkt Och Drivremmar!