Get a can of PB Blaster penetrating oil. Spray the nuts under the manifold and the cat flange genereously, let it sit, and do it again. DO this several times, even for a few days before starting the project (NOT ON A HOT ENGINE!)

The nuts at the flange are 16mm and gave me an opportunity for using my 16mm deep socket for something other than keeping the 15 and 17mm ones apart in the set. A long extension will make life easier (18 inches or so). Mine have come right apart without ill effects but I could be the exception. Those copper flange nuts from the dealer are a requirement. Also use Never-Seize on the threads when reassembling. Get a new flange gasket from a parts shop ahead of time. Remove a couple of the rubber hangers at the front muffler if you can't get enough movement out of the exhaust to get it apart. I'd recommend breaking the catalytic converter flange nuts before taking the manifold nuts off.


As with any exhaust work, be patient, and don't force anything that doesn't want to come apart. Good luck.
--
Rob Bareiss, New London CT ::: 86 244DL, 87 244DL, 88 744GLE, 91 244: 808K total

If the 1989 is like my 1980, besides a gasket you will need some dedicated copper-plated hex nuts for the stud connection to the manifold. The dealer sells them--don't know whether anyone else does.

You can only tighten these one time, so make sure you have everything lined up and the gasket snug. Each nut has an integral "lock washer" with copper ribs on its face. The ribs flatten out when you tighten the nut. If you try to reuse the nuts or even retighten new ones, the ribs get squished out to where they don't bind when everything gets real hot, and your header pipe keeps coming loose. Happened to me several times.

I suppose you could use the old nuts to test tighten. Hmmmm. The gasket may also be a one-time-use. Don't recall--it's been a long time. (Which is good, in a way--once you get it back together right you won't have to mess with it for another ten years.)

Good luck.

Doug Harvey