Author Topic: Manifold -> exhaust nuts & bolts - special? (Read 2157 times)

TheDutch · « **on:** June 05, 2008, 10:12:50 AM »

Hi all,

I am going to have to do something about the front section of my exhaust in the near future, but the existing nuts and bolts are significantly rusted and will probably be destroyed upon removal.

I have just ordered a new gasket from BMW in preparation for this, and was going to get the nuts and bolts too but decided not to when I heard that they were about �13 ($26) for the four of them. Is there anything particularly special about these; are they unusually shaped, or high-temp / strength perhaps? I intend to use some standard nuts and bolts unless there is a good reason not to.

Any knowledge / suggestions gratefully recieved,

The Dutch

Wise Old Dog · « **Reply #1 on:** June 05, 2008, 10:29:29 AM »

Are you describing the 4 bolts that attach the forward section to the header? They are not bolts, they are studs that must be welded on. Stainless steel IIRC. You also will have to cut the old ones off. It would be best if you can remove the old nuts without damaging these studs. The nuts used are copper to keep them from seizing up on the studs. You might get lucky and not have to replace the studs, but do replace the copper nuts.

TheDutch · « **Reply #2 on:** June 05, 2008, 10:40:00 AM »

I am referring to the bottom of the mainfold (i.e. not the head!)

The diagrams on Realoem give the impression that these were seperate bolts. Well that sounds like it could be more of a job. I will have to take another look, but I thought the existing threads did not look great, but they may just be covered in dirt - is that optimistic? Stainless steel would be in keeping with the rest of the manifold though.

I take it that replacement involves drilling the old studs out - is this uncommon, and is it possible without complete removal of the manifold? Sounds like a lot of hassle to me (or maybe an opportunity to hone stainless welding skills and fix a crack in the manifold too.)

peerless · « **Reply #3 on:** June 05, 2008, 11:00:10 AM »

We had removed the header during a engine rebuild. We could not remove all 4 nuts as they where simply corroded on.

We simply used a saw and cut the pipe a few inches rearward of the O2 sensor. Then once we had the header/flange assembly was out of the car we where able to get the nuts off an seperate the 2 halves. To remove the studs, we took it to a local muffler shop and paid $20 to have the 4 broken studs removed. The studs are tack welded to the header.

To reassemble we used grade 12.9 machine bolts and copper nuts from a local bolt where house. We considered Stainless, but we choose the machine screws as they are stronger and black oxide coated for corrosion.

Either way, not a fun or easy job. Your best bet is too heat the nuts up with a torch, a real torch and then you should be able to get the nuts off. All we had was a mapp gas torch and it couldn't get enough heat into the stud/nut to get it to work, the studs just snapped.

TheDutch · « **Reply #4 on:** June 05, 2008, 12:13:22 PM »

Peerless, how long have you had the nut & bolt assembly on for? I wonder whether they allow more movement and the possibility of premature gasket failure. Your method is understandable, but I don't really want to take the manifold off the head if I can help it; it just sounds like the risk of more trouble.