Brazing headers
 

I'm trying to use an early set of heat exchangers as headers. The heater boxes have been cut off so that just the pipes remain (I don't need heat). Within, I've got some small rust holes in the pipes of my headers and some of the metal is extremely thin. I'd like to use them but fear they're too thin to have patches welded. Can you braze the headers, or does the temperature of the exhaust get too high?

You can see them below:
http://www.connorguitars.com/car/Pinholes.JPG

I has a welder at my shop here successfully braze a couple of pinholes in a set of early heat exchangers. The patch is holding up very well.

That being said, when he tried to weld a bracket onto the other header, he was not so successful. It appears that the two headers that I acquired were different metal, one was possibly stainless.

In this case it wasn't a matter of the weld holding up, but rather it was a matter of the metal not taking the weld.

Either way I don't see that you have anything to lose since there will be heater boxes and hence no chance to get fumes in the cabin.

good luck!SmileWavy

Brass brazing is about 2800f on the low side. Silver brazing (or more correctly, soldering) would be a problem at about 1200f.

John

About how hot does the pipe get? Has anyone metered it with a pyrometer? Would 2800 deg. brazing hold up for anything larger than a pinhole fix?

I doubt exhaust pipes get anywhere near that - they barely glow orange in the worst case. I've got a infra-red heat gun here at the plant, but my car is cold right now. I'll zap it tomorrow after I get back from lunch.

The bear about brazing a pinhole is the surrounding metal and the fact that most brass brazing rod love a very, very clean area, plus the pinhole edges must be thick enough to not disappear under heat and simply give you a larger hole. The flux you use to do this will protect the metal, perform some low-level cleaning and prepping as it melts to temp., and help flow, but it cannot make up for a dirty area on which the brass will simply not flow without excessive heat.

You ought to cut the area out as much as you need and create a small like-thickness piece to braze over the hole. Run the brass underneath on all sides and you are done.

John

Typically, normally aspirated engines have EGTs of 1200ºF maximum and this is at the exhaust port. The temperature decreases as it exits the system. As a point of reference, I've measured the pipe directly under the valve cover at around 400º with my infrared temp. sensor. This is at idle. It'll probably be higher at speed.

Here's my suggestion. Braze the pinholes. They should be fine. You can also clean and media blast the pipes with something gentle (glass, walnut shells, etc.), then ceramic coat the system, inside and out. The coating should preserve what's left of the material.

Sherwood Lee
http://members.rennlist.org/911pcars

I think your headers have reached the end of there service life. They appear just to far gone to even justify patching (it looks like the center pipe is split its whole length) While you could braze and patch those holes, Im sure you will be revisiting the pipes to repair other areas even if you have a coating applied to the pipes.

You could try and locate some used 3-1 headers from a salvage yard, or you could buy a set of new headers. GT-Racing sells mild steel headers for about $500 (with street adapters), then you could have them coated with a thermal barrier ($200 from Swaintech or Jet Hot) to preserve the headers and gain some performance.

Or you could buy SSI's for about $850 for the pair.

I think trying to patch up the headers you have would be more trouble than just getting some new ones.

BTW, sweet guitars

Yeah you know, I looked at the pictures...those are more than just pinholes.

:eek:

I just looked at your header pic. Geez they're not quite pristine are they? I see a few pinholes and some gaping holes. If you want to save them, you'll have to braze on sheet metal patches to cover the large openings. Ceramic coating is going to cost a couple hundred (I guess) and with patching, repair and prep, you'll have at least $350 in these in no time.

Go with Tim's suggestion and purchase race headers, new or in good shape. Sell these to someone who wants a project or do the minimal patch job and use until you hear something fall on the road behind you.

Sherwood Lee
http://members.rennlist.org/911pcars

Curious about the guitar reference, I looked at your site.

I take back what I said: there is no way I would try to keep those headers: they are SHOT!

John

The headers may be at the end of their life. I'm going to play with patching patching them with sheet metal. It's ok if they don't last too long. Maybe I'll pick up a new set in the next year or so. In the meanwhile I'm curioius to see what difference they make since I've been running the normal 3.0 headers to date.

BTW the guitar reference is my brother's Web site. I use it to post my images. If you're interested in the guitars just go to:
http://www.connorguitars.com there's a great gallery section.