cat pipe

Discussion in 'Equipment' started by Rad, Oct 4, 2001.

  1. Rad

    Rad Done riding

    Joined:
    Sep 24, 2001
    Oddometer:
    12,174
    Ok, hold on to your ass boys and girls, the following actually has GS content.


    I have a quick question regarding the installation of the cat replacement pipe. When I installed one on my 99S the strong recommendation on the S site was to use blue high temp sealant on the slip fitting. People who did not use the high temp sealant had far more loud back fires from their systems. I also know you can reset the TPS to reduce the backfires. When I asked the head wrench at the local BMW shop he said use nothing. When I took my cat off each slip fitting was covered with anti seize.

    My question is: Which of the following is recommended, sealant, anti seize or dry? I am not talking about any fasteners just the tubing. On all exhaust fasteners I use anti seize
    #1
  2. Sparky

    Sparky .

    Joined:
    Jul 7, 2001
    Oddometer:
    376
    Location:
    Berkeley
    anti seize

    - S
    #2
  3. Rad

    Rad Done riding

    Joined:
    Sep 24, 2001
    Oddometer:
    12,174
    Another view

    Well, with my cat replacement pipe I have had constant scorch marks on the headers and extremely loud back firing. I have tried it now with a completely dry installation, then with anti seize and now with blue high temp sealant. With the first two there was clearly not a proper seal made. Scorch marks appeared quickly at the header cat pipe connection. Even with careful alignment and proper tightening of the clamps the problem persisted. With anti seize the only change was first the anti seize blew out in a couple of small sections then the scorch marks appeared again. Backfiring was incredible. Extremely loud on major decelerations in the mountains, scaring women and children and making grown men cry. With the sealant all blow by is gone. Almost all back firing is gone and what little remains is very muted. About as loud as a discrete fart.

    On my S I had the same problem with the cat pipe but with the rear slip fitting. The recommendation on the S post was the blue sealant and it worked.

    I checked with a well known and respected BMW guy in Austin, Roger Albert, about using the sealant on the GS. He said that in theory the exhaust should work properly without the sealant but he said we all know that theory and reality are not always the same. He said that it should be fine using the sealant if it is not over done.
    #3
  4. dapolrbear

    dapolrbear Buddah Head Adventurer

    Joined:
    Jul 13, 2001
    Oddometer:
    805
    Location:
    Los Angeles
    I used Hi Temp copper silicone sealant, as recomended by Fish. Stuff looks orange.

    With out the sealant I had a slight puff of air coming out where the header meets the y piece, it was coming out of the slits at the end of the y pipe, I cranked it down properly and all but still had a leak. No more problems after the sealant.

    What kind of mess will the silicone leave if I decide to take it apart and make everything stock again?
    #4
  5. fish

    fish Banned

    Joined:
    Jul 6, 2001
    Oddometer:
    47,727
    Location:
    Gold Country
    DPB has it exactly correct. Hi temp copper spooge. There is no substitute.
    #5