MIG Welding an Exhaust Header - CB400T
Close

MIG Welding an Exhaust Header - CB400T

This is a discussion on MIG Welding an Exhaust Header - CB400T within the Technical forums, part of the Caferacer.net Forums category; Hello All, I'm doing a resto/mod on a 1981 CB400T, which is nearly completed. After some urging by jcw I've decided to make a move ...

Page 1 of 4 123 ... LastLast
Results 1 to 10 of 37
Like Tree15Likes

Thread: MIG Welding an Exhaust Header - CB400T

  1. #1
    Senior Member jakejensen's Avatar
    Join Date
    Sep 2018
    Location
    Berlin
    Posts
    127

    MIG Welding an Exhaust Header - CB400T

    Hello All,

    I'm doing a resto/mod on a 1981 CB400T, which is nearly completed. After some urging by jcw I've decided to make a move an get a welder for this project. I am going to go with a MIG welder. A- cuz they're cheap. B- cuz I have only ever used MIG. C - cuz I want to turn and burn some tools for my shop with steel (cart for tools, rolly chair, cart for welder, stand for project bikes) and doing it with TIG seems like a pain in the ass. If I get into welding components for the bike and it turns out I like it, I'll look at getting a TIG machine later. I can get a MIG welder for $50 here in Deutschland, where a TIG Machine will run me 4x that.

    I've got the standard exhaust set up on the bike currently - twin downpipes, the resonator, and twin mufflers. However, for vanity sake (looks and sound) I want to try my hand at welding a 2-1 exhaust for it. Here is a short list of the considerations I've made so far (correct or not so correct!!)-

    1. Resonator.... Ugh.
    So this one has been a head scratcher. After asking around on this forum the concensus is that they do relatively little in terms of performance. The primary contributor to the vacuum resonance that dictates performance on this bike is the air box ( or so I'm told) by providing constant temperature and pressure for the intake. The resonator's primary contribution to the performance of the bike is to add total overall length to the system. Now, if it was removed, what would be the effect on the engine's performance? I've been told pretty much zero. But I can't say from experience.

    2. Calculating overall length
    This site provides an automatic calculator for length of the system based on 2 criteria - http://www.nightrider.com/biketech/c...austlength.htm

    I. midrange RPMs
    II. cam angle of open on exhaust or BBDC ( Before Bottom Dead Center ).

    Now I'm not building a race engine, but maximizing horse power wouldn't be awful.....

    3. MIG vs. TIG welding

    For me, I'm not really in love with the stainless steel look of custom headers. Could that change? I guess. For now I'd be happy to make an functioning 2-1 header with a new muffler, all painted black. So, has anyone in this thread ever welded an exhaust with a MIG welder? Is there any major drawbacks? Have I missed anything in the above considerations?

    Thanks for the help in advance!
    Name:  bike2.jpg
Views: 180
Size:  2.08 MB

  2. #2
    jcw
    jcw is offline
    Senior Member jcw's Avatar
    Join Date
    Jul 2015
    Location
    chicago burbs
    Posts
    2,076
    I have neither encoraged you to MIG an exhaust or start with an exhaust as your first project.

    Be warned i think this is a BAD idea.


    MIG welding projects around the garage is a good first step. Practice on some thin sheet to simulate tubing will tell you if MIG exhaust is practical or not. I suppose you COULD glue metal together with MIG and grind them to look decent, but thats not real welding. The problem is the lack of heat control a cheap MIG welder can provide.
    Last edited by jcw; 03-01-2019 at 07:09 AM.

  3. #3
    Senior Member jakejensen's Avatar
    Join Date
    Sep 2018
    Location
    Berlin
    Posts
    127
    Quote Originally Posted by jcw View Post
    I have neither encoraged you to MIG an exhaust or start with an exhaust as your first project.

    Be warned i think this is a BAD idea.
    Why is it a bad idea?

  4. Remove Advertisements
    CafeRacer.net
    Advertisements
     

  5. #4
    Senior Member 540nova's Avatar
    Join Date
    Jul 2016
    Posts
    107
    I salute your enthusiasm. Mig welding is pretty easy to learn, and most people will be able to lay down a decent looking run within minutes of their first attempt. The challenge comes when your work is not laying flat horizontal in front of you, or is thin. Welding vertical, out of position (upside down), thin, or tubular is when you realize there's more to it. Not trying to discourage you, but definitely practice on scrap tubing before you commit to the tubes you carefully shaped for your exhaust. I think you'll find it looks much better if you use a pulsing technique on your tubing, rather than steady trigger. Think of it like spot welding. I've been using mig for years, and have sold quite a few custom stainless steel exhausts for various bikes, that were back-purged and Tig welded. I would never use a mig for exhaust unless I had no choice.

    Sent from my Pixel 3 XL using Tapatalk

  6. #5
    jcw
    jcw is offline
    Senior Member jcw's Avatar
    Join Date
    Jul 2015
    Location
    chicago burbs
    Posts
    2,076
    What he said ^^^^

    Yeah, exhausts on cars are mig welded but like I said, you cant flip a car over on a table and TIG weld it and no one sees the shitty looking welds anyway.
    Last edited by jcw; 03-01-2019 at 07:14 AM.

  7. #6
    Senior Member jakejensen's Avatar
    Join Date
    Sep 2018
    Location
    Berlin
    Posts
    127
    Quote Originally Posted by 540nova View Post
    I salute your enthusiasm. Mig welding is pretty easy to learn, and most people will be able to lay down a decent looking run within minutes of their first attempt. The challenge comes when your work is not laying flat horizontal in front of you, or is thin. Welding vertical, out of position (upside down), thin, or tubular is when you realize there's more to it. Not trying to discourage you, but definitely practice on scrap tubing before you commit to the tubes you carefully shaped for your exhaust. I think you'll find it looks much better if you use a pulsing technique on your tubing, rather than steady trigger. Think of it like spot welding. I've been using mig for years, and have sold quite a few custom stainless steel exhausts for various bikes, that were back-purged and Tig welded. I would never use a mig for exhaust unless I had no choice.

    Sent from my Pixel 3 XL using Tapatalk
    Is that because the MIG machine is hotter and less precise? In reading about the difference between the two, it seems like that's the major difference. Folks say that TIG allows you to dial down the heat so you don't blow out the material. Is that why you wouldn't use it for an exhaust?

  8. #7
    Senior Member 540nova's Avatar
    Join Date
    Jul 2016
    Posts
    107
    Sorta. With mig, one of the challenges is getting your machine set right, and that's not always easy, plus, you have to adjust your settings as you go, to compensate for the heat build up. The end of a run takes less amperage than when you began, because the metal is now heat soaked. And with mig, that wire just keeps coming out, wether you have the metal hot enough, or not. With Tig, YOU decide when, and how much, if any, to add filler, once you establish a puddle. Plus, with Tig, you have full control of heat/amperage with your foot pedal, so you can dial back the heat as you move along.

    Sent from my Pixel 3 XL using Tapatalk
    jakejensen likes this.

  9. #8
    jcw
    jcw is offline
    Senior Member jcw's Avatar
    Join Date
    Jul 2015
    Location
    chicago burbs
    Posts
    2,076
    You can control the heat input at the machine but then also make fine adjustments as you progress with the foot pedal with TIG. More heat when you start, less when you end. You can also control heat input with the speed you travel with both processes.
    The main issue is the cheaper the machine, the less stable at low amps. It is the stability and control at low amps that you need to weld exhaust tubing.
    Structural tubing and flat plate you can weld with any process. Stick, oxy/fuel, mig, tig.

    Again what he said^^^^

  10. #9
    Senior Member TrialsRider's Avatar
    Join Date
    Jan 2011
    Location
    Ontario, Canada
    Posts
    5,423
    Quote Originally Posted by jakejensen View Post
    ... The resonator's primary contribution to the performance of the bike is to add total overall length to the system. Now, if it was removed, what would be the effect on the engine's performance? I've been told pretty much zero. But I can't say from experience. ...
    I thought the job of the exhaust resonator was to reflect the exhaust pulse noise such that the sounds tend to cancel out one another and make the exhaust sound tolerable.

  11. #10
    jcw
    jcw is offline
    Senior Member jcw's Avatar
    Join Date
    Jul 2015
    Location
    chicago burbs
    Posts
    2,076
    The only thing i would agree with is buying a mig to wet your feet and see if welding is something u wish to pursue. I am sure there are a bizillion cheap and expensuve TIG welders out there whose owners never really got into them.
    540nova and jakejensen like this.

Page 1 of 4 123 ... LastLast

Sponsored Links

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  

Similar Threads

  1. welding exhaust ports
    By roccitycafe in forum Technical
    Replies: 21
    Last Post: 11-07-2015, 04:09 AM
  2. Suzuki GS500 powered Drag bike project on mig forums.
    By nic579 in forum Vintage Motorcycle Racing
    Replies: 1
    Last Post: 08-03-2014, 10:58 PM
  3. TIG welding stainles header - filler Question
    By kerosene in forum Technical
    Replies: 8
    Last Post: 04-14-2010, 11:22 PM
  4. mig welding question.
    By pampadori in forum Technical
    Replies: 11
    Last Post: 08-09-2008, 10:24 AM
  5. Replies: 3
    Last Post: 03-11-2008, 12:42 AM