Stainless exhaust bolts and fittings, advice or link pls.

Hi all, I'm off work the week after next so am getting the bits together to swap the exhaust. Last year I fitted Top Gear boxes but as it just scraped through its last mot omissions (diagnosed as failing cats) I'm going to fit new TG cats, manifolds and lambdas. Can anyone share a link to the stainless steel manifold bolts or studs and the stainless clamps please? Thanks

There is a chance of the original manifold bolts snapping when removing and if you are pushed for time it might be worth planning for that event too.

Thanks, yes I'm expecting the worst!

I'm taking a break from my manifold bolt marathon as I type this. I've just finished replacing all my manifold bolts with stainless studs (well, I've got to pop the studs in on the remaining side, but it's raining and I'm doing it on my drive) On the right side only two of the old bolts undid. On the left it was only one. All the rest had to be drilled out. I found the only use for my stud extractor was for snapping off a could of bolt shafts, saving having to cut them short as per the Stomski jig instructions. It's taken three days to do the job. If you have the money, it's well worth paying a specialist to do this for you as it's a total pig even with the right tools. Without the jig you wouldn't stand a chance. I had previously replaced all the other bolts on the exhaust system with stainless and it meant that none of those gave me any trouble whatsoever. Look on Ebay for stainless nuts & bolts, A2 stainless is fine. A lot of internet nerds will spout crap about metallurgy and stainless hardware not being suitable for all sorts of spurious reasons. The fact is, it works, it's strong enough, and it won't be brown dust in five years' time like the Porsche hardware.

I know its been discussed here previously and people will say it isn't an issue, but generally speaking putting a stainless bolt or stud into an aluminium hole (ie the head of a porsche) is a very bad idea, as it will corrode, and if you try to remove it in the future and it snaps (as it will because they arent as strong as plain steel), it will be extremely difficult to drill out... far more difficult than a traditional steel bolt/studs that are currently a massive pain to do... if you do go down this route make sure you used brass nuts which are soft enough to get off the stainless thread without drama, dont use stainless or steel nuts... I'm not sure whether titanium suffers from the same corrosion in aluminium as stainless steel?

I'm by no means knowledgeable on the subject, but I did find these articles which cover the risks of corrosion: https://www.bssa.org.uk/topics.php?article=89 https://www.npl.co.uk/special-pages/guides/bimetallic-guide As you'd expect from the National Physical Laboratory, the latter seems to provide pretty thorough coverage on the topic.

Thanks Martin, I feel you're pain! I'll definitely be using a jig and I have a lift at home plus I'm too tight to pay a £100 a stud so I'm going in with fingers crossed! Thanks for the comments and info re the type of studs, some good points from both sides. I'll read the articles when I get a bit of down time later.

The table in link 1 would appear to indicate that titanium is a worse idea than stainless... I had thought that maybe copper grease would be a good barrier but manifolds get far too hot for it to survive, is there a high temperature alternative that could be used on the threads?

[quote="Hertsdriver"The table in link 1 would appear to indicate that titanium is a worse idea than stainless... I had thought that maybe copper grease would be a good barrier but manifolds get far too hot for it to survive, is there a high temperature alternative that could be used on the threads?[/quote] Sorry, copper grease is no good on ally either, similar corrosion issues. Ally grease is readily available (you should be using it on your wheel nuts!)

Hertsdriver, can you suggest a better alternative than stainless based on your experience? Correct me if I'm wrong, but it looks like you're saying that using stainless fixings is a bad idea because of some stuff you found on the internet. The original Porsche fixings are made of plated mild steel. Their dissimilarity to aluminium means that there will always be galvanic corrosion of both materials. If you change one of those materials to one that doesn't corrode (yes, yes, I know stainless does corrode eventually, but for practical purposes it will last 10 years on an exhaust) then you leave yourself with half the corrosion problem that you would have had. Given the mild steel bolt will corrode as well as the aluminium bore it's in, the two will mechanically lock themselves together and at the same time as weakening the bolt. When torque is applied to the bolt it frequently take more torque than the weakened bolt can withstand to undo it. Ping! I heard that ping on nine out of twelve manifold bolts in the last couple of days. :nooo: If you've used a stainless bolt, the corrosion of the bolt won't happen, so the mechanical locking won't happen, and the bolt will be pretty much as strong as the day you put it in. You also say that stainless is softer and therefore is harder to drill into if the fixing snaps. This doesn't make any sense. If softer materials were harder then I would make a hammer out of playdough. Sorry if any of this comes across as confrontational, it's just that having just spent three days skinning my knuckles underneath my car, partly in the pouring rain, it really grips my sh!t when people who haven't done the same (and I'm assuming you haven't, so apologies if you have) give bad advice based on hearsay. The consequence of this is that some poor ***** out there in the real world could read it and choose to either spend a fortune on wonder-bolts unnecessarily, or worse, install the original Porsche hardware, which will corrode to nothing in a few short years. I use stainless in all sorts of applications across my 911, and having done this for six years, every one of the stainless fixings I've used has done its job and not caused the hole it's been screwed into to corrode beyond use. I've lost count of the mild steel fixings that I've had to drill out, hammer out, snap off, etc. I'll continue to use stainless based on my experience with it until someone comes up with a tested equivalent that works better and is reasonably comparable in price. If the stainless fixings I've used come back to bite me in the bum and my helicoil skills can't save me, I promise to come back here and own up.

Hmmm.. Can I advise on something better? No and I'm not sure I said I could. I am learning from what I've read here and elsewhere and trying to participate in the discussion, apologies to you if you think that my participation in this thread warrants your abuse and ridicule. Was it my comment about using brass nuts rather than stainless that 'got your giat' I'm not sure I said stainless was soft did I? Perhaps you can point out where I did? It certainly isn't soft, it's significantly harder than steel but it doesn't have the same torsional strength as steel, because it's far more brittle. That's why I personally don't like to use it in situations that require strength (like wheels, and to some degree, replacing bolts in places that require torque). If I were to proffer an apparently (un)educated opinion, I would suggest that a good grade steel stud, installed with an anti galvanic grease (alloy grease as mentioned by another) installed at a sensible torque and then fitted with brass nuts would probably be more than adequate. It certainly used to work very well on older cars, and despite the increase in technology I am not sure exhausts on a 996/997 get significantly hotter than they do on older performance cars, or perhaps you can put me right on that? My opinion on 'what went wrong' is that Porsche used cheap bolts, both in the fact that it's clearly cheaper to used a bolt than a stud and washer/nut, and the material is obviously substandard. I am interested to hear about how 'the mild steel bolt will corrode as well as the aluminium bore', as that seems to fly against the laws of physics for galvanic corrosion... :thumb:

You mentioned in this passage that stainless bolts 'aren't as strong' but will also be difficult to drill out. In my very recent experience, the weaker something is, the easier it is to drill. In your reply you've moved over to brittleness vs hardness which makes more sense. I'm not sure where to start on how replacing a mild steel stud with a non-specific 'good grade' of steel (though naturally not stainless) isn't exactly a quantumn leap in sensible. I like your brass nuts though. :thumbs:

Just a 'sorry, I read back and you didn't actually say it was soft' would have sufficed. :floor: If Porsche had of used plated steel studs and brass nuts, we wouldn't even be having this conversation, as the brass nuts would have unwound from the stud, and there would be no reason to have to drill anything out (unless the grade of steel used was so poor that it rusted away, which is a distinct possibility...). So what would I use? Probably a stainless stud with a brass nut. There is clearly no need for titanium, I'm sure we can both agree on that, but I maintain that a good quality, possibly galvanised or zinc plated steel stud together with a brass nut would most likely suffice :thumb: In reality this is one of those situations where we are going overboard because of the pain and/or cost of sorting the issue, so the natural want it to replace with something 'better', in reality it's unlikely anyone changing a manifold will do it again, so all the effort is more than likely only if benefit to the next owner.

Mine replaced with Inconel. https://en.wikipedia.org/wiki/Inconel I used to be a welder in a very hash marine and refinery environment and gained considerable respect for its ability to take heat and cooling and not rot or warp... There are plenty of suppliers, not particularly cheap, but i would expect them to outlast the car https://www.ebay.com/itm/INCONEL-TU...294597?hash=item2a831c45c5:g:zq8AAOSwIKZdRHwE maybe as above link? I have some 718 bolts that i used in my bits bin, but the above are studs and copper locking nuts, prob a fairly good choice. Or as mentioned above, go S/S as its unlikely to be needed again in the life of the car.

Didn't Poppopbangbang come up with a solution? http://www.porschetistuds.co.uk/