[bmwpower603]

I want to change my exhaust hardware, and the gasket in between the downpipe, and midpipe.

As you can see it’s pretty rusty. Is it worth changing? Is there a chance that I’ll make this even worse, and more leak prone?

[nsjames]

it's been a minute since I looed under mine.

through bolts or studs?
studs are gona suck.
through bolts, cut them off and replace the bolt hardware. The faces of the flanges are gonna be fine.

clean that whole mess up with a wire wheel before you start.

[CTinline-six]

If you don't need to replace it, I would leave it alone.

[DieselOG]

Originally Posted by CTinline-six

If you don't need to replace it, I would leave it alone.

Agreed, I would not touch this unless you absolutely have to

[bmwpower603]

I was looking to get this done at a bmw shop. Incase I had to drop the exhaust, for rear drive shaft service, or if I wanted to get a cat back exhaust.. (And for piece of mind that it won’t leak in the future. I have already purchased all of the hardware, and new exhaust gaskets.)

I really didn’t want to wait for it to rust more before having this issue fixed.

[Needbmwpartzz]

if its not leaking i wouldnt touch it.

[coolmac]

What is holding it together and it is leaking. How should a remove these bolts.

[e90yyc]

If you’re doing it yourself, be prepared to angle grind or drill out the bolts.

[6ixSpd]

Yeah that's exactly how mine looked when getting headers installed with a friend. The bolts were a huge pain. They all snapped and were corroded so badly, no socket would fit on to them. Eventually the best solution was to cut the end of the stock headers just so we could drop the exhaust...

I would NOT mess with those unless you're prepared to cut some stuff off and deal with a headache that was unnecessary in the first place.

[PhaseP]

Originally Posted by coolmac

Attachment 1991788 What is holding it together and it is leaking. How should a remove these bolts.

Had to deal with that myself this fall. New England car 2006 make. Mine was actually worse than that, yours at least have the flanges intact still.
And I have an N52 NA engine. No turbos and related piping that side of the engine, you have a 335 from your signature, things maybe different.

What is holding them together? Rust corrosion.

First thing, those are not bolts, they are studs and press fit; unless have been replaced since factory build. Which they don't look like they have been replaced.

The nuts all corroded away looks like from the picture. If they did completely corrode away then you don't need to worry about them. Otherwise you need to cut or grind the nuts along with the sticking out remaining part of the studs first, since it doesn't look like you can put and hold anything on whatever is remaining on the nuts.

I had ended up cutting pipes close to those flanges, removing the exhaust manifolds from the engine and then taking them apart easily on the bench by one or two blows with a rubber mallet.

Then first I drilled out two of the studs, which took too long and was not easy to make sure I had dead center and straight drilling out them.

Then I decided to try torch next. Heated up both ends of the stud red hot. Then hammered the end of it driving the red hot stud out. Worked out much better and with shorter time.

After that put the manifolds up back on engine. Replaced the studs with bolts and put copper nuts and new gaskets. Those are replacement parts for them and you can find the part numbers at realoem.com or similar. (My flange stud/bolt holes also corroded away, I had to build up on them with a simple welder I have.)

Tied the rest of the pipes temporarily with some exhaust clamps. Someday will get them welded.

Now after all that experience and what I learned, if I were to do it today, I wouldn't cut any pipes and definitely wouldn't touch the exhaust manifold and remove the manifolds from the engine. Instead I would grind away, cut any remainder of nuts while under the car. Knock the pipes separate still under the car hitting with a mallet. (Need to undo any tie downs up to let the pipes move free as much as they can)
Then heat the studs red hot with torch still under the car, and hammer them out. When I say hammer out, you really need to hammer hard, but it takes two three very good hits to get them out if they are red hot.

This way I wouldn't had to cut any pipes, plus I wouldn't be dealing with removing and putting back the exhaust manifolds which was not small amount of work. The nuts and studs on the engine block also were corroded, plus O2 sensors, and had to drop the frame to get them out. Better avoid doing all that.

[Efthreeoh]

Originally Posted by 6ixSpd

Yeah that's exactly how mine looked when getting headers installed with a friend. The bolts were a huge pain. They all snapped and were corroded so badly, no socket would fit on to them. Eventually the best solution was to cut the end of the stock headers just so we could drop the exhaust...

I would NOT mess with those unless you're prepared to cut some stuff off and deal with a headache that was unnecessary in the first place.

I had to deal with this problem the last time I removed the exhaust to replace the driveshaft. I had taken the exhaust off a few times prior, using penetrating oil (Kroil - the BEST stuff on Earth) long with air impact tools (and on my lift - so it was easy to get good purchase on the nuts) and was able to reuse the hardware. I also re-installed everything with high-temp copper anti-seize.

However, during the driveshaft removal, the nuts finally gave up the ghost. I've had other cars do this, and the solution is to simply cut the studs flat to the flange, then hammer them out with a pneumatic air hammer. No go with the E90. The studs get welded in place (at least mine did). I tried mapp gas for a bit, but I was afraid of cooking the O2 sensors. So I took to drilling the studs out. THAT is a complete pain in the ass. The stainless steel gets very hard from heat cycling. I could drill no larger than a 3/8th hole (off center of course ). Keep in mind all this was under a lift, standing on my feet and at a good angle to drill, pressing hard on the drill, and using industrial twist drills (not the shit the hardware store sells for mild steel).

So I ended up using Grade-8 3/8th hardware. Don't try using stainless steel hardware thinking it will not corrode. Stainless steel hardware from the hardware store is very soft and can easily snap off.

Leave it alone until you have to actually remove the exhaust. It's not leaking; it's just RIP (rusted in place).

[coolmac]

Thanks for all the help but, my exhaust is leaking. I don't have a left or a air hammer. The 335i is a 2009 with 70K miles, very poor choice of stud and or bolt metal from BMW. To the shop it goes. Thanks

[coolmac]

Originally Posted by coolmac

Attachment 1991788 What is holding it together and it is leaking. How should a remove these bolts.

I bought the gasket and bolts from Ebay ($36), i had a Muffler Shop install, that was for $50. What's next.

[freakystyly]

Mr. big shot over here that still has flanges.

Winter road salt seems to eat those things like crazy once it starts, they just go quicker and quicker.

I had done the same thing with mine a couple years ago and was able to put in new bolts. This year the leak reappeared and there was nothing left of the flanges, just nubs where they should be. I had a mechanic throw on some weird cup shaped flange clamps for lack of a better term. They seem to fit over top of the existing ends. Unfortunately I think that is just a temporary fix. I think they're leaking again 2 months later.

Is the exhaust material just thick walled steel? Would stainless pipes / flanges last longer? I heard that oftentimes welds would create weak points that will fail with rusty conditions too.

Thinking of an excuse to throw on some supersprint or AA pipes / headers.

[PhaseP]

Originally Posted by coolmac

I bought the gasket and bolts from Ebay ($36), i had a Muffler Shop install, that was for $50. What's next.

Good call and move.

[PhaseP]

Originally Posted by freakystyly

Is the exhaust material just thick walled steel? Would stainless pipes / flanges last longer? I heard that oftentimes welds would create weak points that will fail with rusty conditions too.

Pipes are stainless steel, welds too. If they weren't mine would have been already in pieces after 13 years of New England salty roads. I am not sure about the flange material.
If they leak again an exhaust shop could be your solution. They could weld up the flanges, which would be good but not good for serviceability if you need to take out the exhaust manifolds every. They can also weld new replacement flanges. And if you have enough flange left for the gasket surface but only where the bolts/studs go have corroded away, they could build up those areas with weld, redrill holes and bolt it up again.