Manifold to cat studs/ nuts corroded, pointers for removal please?

Morning All, I'm looking to replace the cat sections on my exhaust in the coming weeks. I serviced the car the other day and had a glancing look at the manifold/cat flanges and whatever is holding them together looks rather corroded. From searching, it sounds like these are typically stud/ nut, stud being in the cat section? What I have looks like it may be a nut and bolt but heavily corroded. My engine was rebuilt some 40k/ 10 years ago, going off the history so this may well be the case. So I'll just have to see how it goes trying to remove these fasteners. I was looking to take off the rear bumper/ heat shields for better access. Am I unlikely to get the 02 sensors out of the original cats or does it just take a bit of heat/ perseverance? Any pointers appreciated! Cheers, Scott

Soak them in some PB blaster or equivalent. Hopefully during the rebuild they put some antiseize in the threads to help them break free... I found that 2 of my O2 sensors were ok to remove, one was damaged on removal and one was stuck permanently in

Quotes source post: 2716581

Cheers for the reply, Jay

Before you spray whatever magic release liquid you care to use, might be worth giving the fixings a bit of a scrub with a wire brush, to remove the loose crud that can prevent the spry getting to where it might ease the process a tad...? Best of luck in terms of your planned task.... All sorts of vids on the www to help.

OK so I am somewhat of an expert having recently worked my way through the rusty remains of my exhaust nuts and bolts !!! Don't bother wasting your time and money on penetrative fluids ...you'll waste time,money ,patience and skin...if you can't remove it take it somewhere and get them to cut ,grind and remove each section of the exhaust and then buy some stainless nuts bolts etc and marvel at your ability to remove parts of it at will I removed the complete exhaust as my manifold bolts are stainless so no problem to get off and took it to an independent (sans silencers ) whom spent a few hour's with proprietary tools and heat to remove brackets and flange bolts ...they could not remove the 02 sensors so... I ended up buying from designb911200 cel cats ,4x bosch sensors and all of the exhaust hardware ...came out of the other side £2000 lighter but with a system easily dismantled : including exhaust trims etc so pleased ultimately ...no way I would have wanted to wrestle with this in my garage ... 80% of the 996s around will have stuck manifolds and exhaust sections thus my rationale ,perverted I agree, was should I sell then this expense might be a good selling point ??? And the pleasure in being able to just easily remove bits of the exhaust was unbelievably satisfying ... Oh and at the same time I replaced all the plugs and coil packs ... Bon Courage if you tackle this on your own

I did the same as GMG. The studs were a mess so I cut them off and drilled the remnants out so I could secure them with new stainless nuts and bolts.

It's a ballache but ultimately satisfying ...just don't waste your time on penetrating sprays unless the nuts and bolts look like nuts and bolts if they don't you'll need heat and power tools ...

I did mine in November, spent about 4 weeks in total, just working on one bolt at a time. (Heat/cool, drill, hammer etc) Replaced with Topgear 200cel cross pipes and bought new o2 sensors from ebay (attached).

Thanks for all the replies guys, I just needed a bit of encouragement haha I'd ordered the Top Gear 200cell X pipe whilst on the Christmas beers and an eBay offer came through so I wanted to be sure I could get all of this apart! As I suspected, mine has been a part before and the cat/manifold flanges were secured with a nut and bolt (at least that's what I think they used to be!) A couple of hours in the garage: 20241227_162844 by Scott Osborne , on Flickr Today, this is what success looks like: 20241227_164734 by Scott Osborne , on Flickr 20241227_164740 by Scott Osborne , on Flickr 20241227_172829 by Scott Osborne , on Flickr 20241227_175341 by Scott Osborne , on Flickr Lambda sensors are all well stuck in so used the same eBay link above, 7% off multi-buy discount and also 10% eBay Christmas voucher. I'm looking forward to the parts showing up now! Thanks again for all the encouragement!

Great job! I replaced mine with fancy metal fixings (titanium and brass) because I never wanted to do rusty stud removals again

Quotes source post: 2716696

Cheers Jay, I've gone for the more peasant version of stainless and copper The new X pipe comes with gaskets and hardware but the gaskets look rubbish and hardware is mild steel so I've ordered the above and proper factory type gaskets.

Really and genuinely well done and the gasket set that came with my top gear 200 cel cats look crappie but are better than the oe porsche ones I discarded because they are thicker so I used them instead better ,tighter fit... And the satisfaction you'll now get knowing that it's all easily dismantled is worth the pain.. You did better than me on the sensors ...mine were a 100 quid each!

Quotes source post: 2716808

Thank You! I will reconsider the gaskets once I have them all in my hands, new OE type from Elring were only £11 delivered so it seemed a no brainer. I'm looking forward to getting the X pipe and getting it all back together, that's for sure! I'm really happy with the deal on the sensors, I started off seeing £140ea, then some at £100ea, which I thought I was going to have to deal on! I'll update this thread as I go so it might give future searchers some motivation too haha

I can highly recommend Parts in Motion if you need anything in future. Bosch sensors are £56 or £69 and they usually have some kind of discount available. Switches and Sensors We stock over 250,000 car parts at the lowest prices from the biggest brands. Fast free UK shipping. Our website helps you find the correct part. www.partsinmotion.co.uk

Quotes source post: 2716874

Cheers Barry, that's who I used through eBay, £234 all in for 4, which I was pretty happy with.