Hot Rod Forum banner

fillet welding header flange gaps

10772 Views 10 Replies 3 Participants Last post by  001mustang
How do you fillet weld a 3/8" steel header flange to 14 Gauge primary tubes with out warping the flange?

Will oxygen/Acetylene No 2 tip with bronze/flux rod suffice?

Should I stitch weld 1" sections to avoid overheating and warpage?

If I bolt the header to an old head then it takes longer to get enough heat to the flange.

I have seen bronze fillet welds pull loose from a 1/4" flange after welding port on opposite side of flange.

I have heard of Mig braze welding but don't know if it is good for this operation.
1 - 11 of 11 Posts
It's usually better to weld the tube to the inside of the flange , then surface the flange after welding..
But if you are just welding the outside, bolting it to an old head and TIG welding is the way to go.

If I were going to gas weld it, I'd use silicon bronze brazing rod, it has a higher tensile strength compared to straight bronze, doesn't warp the steel as much as steel filler rod and you don't need flux. You can make a nice bead with it too.

After you weld it up, you can build up the inside of the flange by migwelding a bead around each port, then surfacing the flange. It makes for a much better seal.

I understand you use silicon bronze wire in a MIG when you do migbrazing, but it doesn't sound like a good plan to me..I never tried it, but I would think 3/8" has to be a hard one to get any penetration with bronze, unless you preheat it...I could be wrong about that.

I think a guy would not get a good looking MIG weld when welding 3/8" to 14 G.

Later, mikey
See less See more
I like the silicon bronze with no flux idea.

The header is already welded on the head side. I am just trying to fill in the gaps on the outside.

Before... I bolted a header to an old head to try and minimize warpage while fillet braze was hard to braze when the head was sucking all the heat away.

Will a 3/8" flange warp while braze welding it?
001mustang said:
I like the silicon bronze with no flux idea.

Will a 3/8" flange warp while braze welding it?
Probably not.
Later, mikey
fillet weld 3/8 flange warped

I bought a pair of JBA 3/8" flange headers and fillet welded seams with oxyacetylene and bronze rod. I welded by making 1 inch passes then going to next tube. I guess I welded to slow.

The 3/8" flange warped.

Any one know how to fix the warped flange?


See less See more
sawsall time

I have seem cuts maed to only leave 1/4 inch metal remaining to hold the tubes in position. and some guys know where to heat the tubes to get them to shrinkand warp in the right direction to pull back into position.
So you can heat tubes strategically to straighten flange?

Any body know the technique?
heat warp.

when we were making pipes for the harley factory the design engineer had the fixtures aligned, lasered and dead on. the problem was when the welder finished them they would cool and warp. I had a hard time convincing the engineer to adjust for kentucky windage. weld one, them measure after it cools and figure out how to adjust the fixture crooked so when it cooled it would end up straigh.
Interesting post.

I noticed the JBA flange I have not yet heated is warped like a banana but the primary tube ports are machined dead on flat.

I am planning to experiment using the assumption that warpage occurs during cooling. On that basis, I figure if I heat a tube in the middle the result will be shortening of the middle tube I heated?
I'd bolt it to a head so the flange was flat, and heat up a 3/4" wide band around to cherry red on each tube and let it cool bolted on the head. Trying to learn to do the heat and shrink on a set of pipes already welded to a common flange will be an exercise in frustration.

Later, mikey
Figured out how to straighten header flange

What did not work for me:

I tried the the lesson of frustration of strategically heating the tubes which did not go well. May work if you are talented.

I bolted header to head and heated tubes to cherry red which did not work for me. When I finished this operation the flange was still warped about 1/8" max. Maybe this would help if flange is warped badly.

What did work:

I used sheet metal shims for leverage then bolted cold header to a spare head; I suppose bolting to 1/2" plate would net the same result. I can move any tube up or down plus I can twist any tube. If you go through a few iterations you can completely straighten a 3/8" header flange with 14 Ga tubes. Once the flange is straight then draw file the primary tubes to verify straightness.
1 - 11 of 11 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.