[V6-12v] Experience changing cats

[Frank Chapchuk]

Tom,

There are studs in the header. When I did mine I was able to remove the cats 
by either taking the nut off or breaking the stud. Breaking the stud is no 
big deal. With the cat out of the way I just drilled out the broken stud and 
replaced it with a stainless steel bolt and nut. No need to tap the header 
to install a new stud. Just use a bolt.

I replaced both cats......after failing emissions. Make sure the O2 sensors 
are working correctly or the new cats may get runied. Mine just died from 
old age.

Frank

----Original Message Follows----
From: "Tom Christiansen" <tomchr at gmail.com>
To: "Audi list" <v6-12v at audifans.com>
Subject: [V6-12v] Experience changing cats
Date: Sun, 4 Mar 2007 14:08:48 -0800

Folks,

As I was crawling around under my 1994 90S (B4) patching the down pipe
for the driver's side cat with Quicksteel, I discovered that the cats
shouldn't be as hard to replace as I had feared. Everything is
reasonably accessible. Most of the bolts downwind of the cat look
pretty pristine, but I wonder about the three nuts on the exhaust
header. On most cars those are notorious for seizing up. But I noticed
that they are lock nuts. So maybe I could be in for a bit of luck...
Does anyone have experience to share in this regard?

Is it three studs in the header? Or three bolts? Will I need to cut
the bolts or do the nuts generally come off without too much fuss? Are
the bolts secured from the top so they won't spin as I turn the nuts?

Would you replace just one cat? Or is it normally encouraged to
replace both at the same time?

Thanks,

Tom
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