E39 exhaust flange repair

[lufbramatt]

In the process of getting my old e39 back on the road. Noticed that the cast iron flanges on the bottom of the cats are crumbling away to nothing.

Don’t want to pay for new cats for the sake of it. What’s the best way of sorting this? The diameter of the pipes is 47-48mm (need to borrow some callipers and measure properly). Have noticed there are split flange kits for e46 M3 exhausts, anyone know if they would be the same diameter?

Or anyone know of a source of repair flanges that are the right size? Can only seem to find 50mm + ones.

[finlo]

Chop them off and replace with something like this?

[lufbramatt]

Did think that, but the pipes are quite curved and there’s a bracket that attaches using two of the flange bolts which takes a fair bit of weight, so need to keep those bolts in the right place.

[996Keef]

Deffo an advert for not using stainless fasteners in cast iron. Makes them rot away to nothing very quickly

I reckon you'll be OK with the m3 ones, just measure to be sure. Are they the aftermarket ones that split in two and are held together by bolts ? Clever solution

[lufbramatt]

Yep these ones

https://x8r.co.uk/over/M3E46Flangekit.html

Just need to know what the diameter of the m3 pipes is.

ETA- pretty sure the m3 pipes are bigger than the 3 litre pipes

Edited by lufbramatt on Saturday 26th March 19:38

[finlo]

Looking at the state of the clamps there may be little or no flange left to clamp!

[lufbramatt]

The pipes inside are fine, I've had them apart before. It's a stainless exhaust on these. The flanges were ropey then, about 5 years ago. Seems to be a common issue, hence the existence of the m3 repair kit but no one posts how they resolved it.

[E-bmw]

lufbramatt said:

It's a stainless exhaust on these.

That is not a stainless exhaust, the bolts are, the support brackets are, but the exhaust that is shown in that pic is not stainless, that much is clear to see.

[lufbramatt]

A magnet won't stick to it. It's not a very high grade stainless, but it's certainly not mild steel. That exhaust is 20 years old. Stainless doesn't stay perfect and shiny forever.

[DVandrews]

Maybe I’m dumb, but can you replace the flanges that easily, the flare on the pipe usually constrains their removal and replacement.

[steveo3002]

id have that into a custom exhaust place , good chance they have something to repair it ...imagine the last inch or so needs cutting off and a new flared pipe + flange needs welding on