[docnabimmer]

so my exhaust flange gasket is leaking bad on drive back from thanksgiving in Durham NC.Replacing the rusted bolts and flange gasket with new ones,BMW M10x40 bolts are like $20 each (need 4) but copper nuts are 0.99 each with the gasket at around 10.
asking because FCP sells a Volvo combo of 3 M8 bolts with 3 copper nuts for less than $4 each set...
so as title states would it be okay to use M8 instead of M10 combo on the downpipe flange.
TIA folks...

 

[kaboom28]

so my exhaust flange gasket is leaking bad on drive back from thanksgiving in Durham NC.Replacing the rusted bolts and flange gasket with new ones,BMW M10x40 bolts are like $20 each (need 4) but copper nuts are 0.99 each with the gasket at around 10.
asking because FCP sells a Volvo combo of 3 M8 bolts with 3 copper nuts for less than $4 each set...
so as title states would it be okay to use M8 instead of M10 combo on the downpipe flange.
TIA folks...

When you say exhaust flange, do you mean where the headers connect to the exhaust? If so, those are special inconel bolts that are pressed into the flange. Have you already removed the pressed-in bolts? If not, be aware that they can be a bear to remove due to their hardness and the fact that they are pressed in.

To answer your question, you can use different size bolts and nuts as long as you can create enough clamping force for the gasket to seal. However, because of the high temperature and where those bolts are located, you want to really make sure you use bolts/nuts that won't rust to hell in 6 months.

 

[docnabimmer]

When you say exhaust flange, do you mean where the headers connect to the exhaust? If so, those are special inconel bolts that are pressed into the flange. Have you already removed the pressed-in bolts? If not, be aware that they can be a bear to remove due to their hardness and the fact that they are pressed in.

To answer your question, you can use different size bolts and nuts as long as you can create enough clamping force for the gasket to seal. However, because of the high temperature and where those bolts are located, you want to really make sure you use bolts/nuts that won't rust to hell in 6 months.

yeah header to exhaust bolts- it was your post that really makes me weary about using non BMW inconel bolts, i may just get the BMW bolts to be on safe side...

 

[///Mark_D]

I replaced the four studs on the flanges with 316 Stainless Steel bolts and lock nuts. They are holding up fine after 3 years / 75k miles. The BMW copper plated nuts would always get extremely rusty and I was having to cut them off each time I removed the exhaust. That is no longer the case w/ the stainless hardware.

Metric hex bolts, Stainless steel 316 (A-4), 10mm x 1.5mm - Bolt Depot

www.boltdepot.com

Metric flange nuts serrated, Stainless steel 316 (A-4) - Bolt Depot

www.boltdepot.com

 

[Inlajnsiksbenzin]

I’ve been running M8 bolts and nuts there for 2 years no problems with leaks whatsoever. They rust badly because I’m using standard zinc plates bolts but whenever I’m under the car I change them. If you use stainless bolt and copper plated nuts I’m certain that it will hold up no problems.

 

[Alex323Ci]

When you say exhaust flange, do you mean where the headers connect to the exhaust? If so, those are special inconel bolts that are pressed into the flange.

you sure about that? i believe the BMW replacements are Inconel but the original studs are not.

 

[kaboom28]

you sure about that? i believe the BMW replacements are Inconel but the original studs are not.

I'm not aware that the original bolts were not Iconel, so if you have better information, then I stand corrected.

 

[Alex323Ci]

I'm not aware that the original bolts were not Iconel, so if you have better information, then I stand corrected.

the fact they rust is pretty evident they’re not.

 

[kd7iwp]

Those studs would be miserable to remove. I had a shop use their MAP torch to remove the studs and have been using stainless hardware for years and it's working great. Well-worth it for any time I need to remove the exhaust.

 

[docnabimmer]

I replaced the four studs on the flanges with 316 Stainless Steel bolts and lock nuts. They are holding up fine after 3 years / 75k miles. The BMW copper plated nuts would always get extremely rusty and I was having to cut them off each time I removed the exhaust. That is no longer the case w/ the stainless hardware.

Metric hex bolts, Stainless steel 316 (A-4), 10mm x 1.5mm - Bolt Depot

www.boltdepot.com

Metric flange nuts serrated, Stainless steel 316 (A-4) - Bolt Depot

www.boltdepot.com

Thank you for this info Mark and that is awesome considering where you live that these SS bolts last that long....
And I'm paying a muffler shop to swap out the bolts

 

[kaboom28]

the fact they rust is pretty evident they’re not.

I live in an area where rust is not a concern. When I dropped my exhaust to do the CSB and guibo at 200k miles, I only needed a ratchet to remove these nuts. No rust on the bolt or nuts, as a matter of fact the nuts were good enough to reuse even though I purchased new copper nuts . Obviously YMMV when it comes to rust.

 

[kaboom28]

Thank you for this info Mark and that is awesome considering where you live that these SS bolts last that long....
And I'm paying a muffler shop to swap out the bolts

Muffler shop ........

 

[Alex323Ci]

I live in an area where rust is not a concern. When I dropped my exhaust to do the CSB and guibo at 200k miles, I only needed a ratchet to remove these nuts. No rust on the bolt or nuts

the whole thread is about how these down-tube bolts/nuts are rusted and need to be replaced.
there’s other signs besides being rusted. they’re not Inconel from the factory.

 

[kaboom28]

the whole thread is about how these down-tube bolts/nuts are rusted and need to be replaced.
there’s other signs besides being rusted. they’re not Inconel from the factory.

Like I said earlier, I stand corrected.

 

[Alex323Ci]

Like I said earlier, I stand corrected.

haha yeah all good. 🙂👍🏻

 

[TobyB]

I think mine have been held together for the last 5 years with 5/16"
grade 3 bolts from the hardware store.
When they next come off, it'll be easy with a 1/2" drive breaker bar.
And cheap to replace 'em, too.

Yes, the factory studs are made of SOME sort of very high tensile,
low rust material that LOVES to gall whatever nut's put onto them.
But I too have seen them seriously corroded. Even in our
low- corrosion environs.

t

 

[docnabimmer]

Shop will change 4 bolts and nuts with stainless steel bolts nuts like Marks and 2 Elring gaskets.My bolts/studs and nuts are rusted original ...
$175 parts and labor.Go or no?
Tia.

 

[kaboom28]

Shop will change 4 bolts and nuts with stainless steel bolts nuts like Marks and 2 Elring gaskets.My bolts/studs and nuts are rusted original ...
$175 parts and labor.Go or no?
Tia.

That feels like $25 for parts and 1 hour of labor? How much is your time worth? Would you be able to complete the job if the bolts/nuts get mangled? Will you be able to get the pressed-in bolts out of the flanges? Only you can answer these questions.

 

[docnabimmer]

That feels like $25 for parts and 1 hour of labor? How much is your time worth? Would you be able to complete the job if the bolts/nuts get mangled? Will you be able to get the pressed-in bolts out of the flanges? Only you can answer these questions.

True- if it was warmer out if give it a try .but the weather here is jersey had gone "life below zero" I don't think I would be able to tackle this even in the garage..
Parts definitely inexpensive ...labor is the killer but I would do a CCV RR and a front axle RR on an XI than this exhaust bolts.
Thank u for the input.

 

[docnabimmer]

I think mine have been held together for the last 5 years with 5/16"
grade 3 bolts from the hardware store.
When they next come off, it'll be easy with a 1/2" drive breaker bar.
And cheap to replace 'em, too.

Yes, the factory studs are made of SOME sort of very high tensile,
low rust material that LOVES to gall whatever nut's put onto them.
But I too have seen them seriously corroded. Even in our
low- corrosion environs.

t

Thank you Tobyb so it seems 8mm will suffice if the 5/16th in bolts held up for tye last 5 yrs for you.
Ill get some M8 and M10 SS bolts nuts when I try to do this job myself next summer for the sedan.
To close this thread - shop used M10 x40 SS bolt/nuts.They would not want me to provide the parts....