MIG welding exhaust question

[mopowers]

I've been piecing together the exhaust in my 68 by joining the existing pipes with the newly installed headers using some mandrel U-bends I bought. The joints that I need to weld up are all butt joints with 16g pipe.

My question is when you guys weld up butt jointed exhaust tubing with a MIG, do you use a continuous bead /weave pattern, or is it best to stitch weld the joint by using short overlapping tacks??? Just curious what technique you folks use.

 

[pishta]

Ive only welded rusty thin old stuff, but can tell you a continuous bead always burned through on me. little overlaping stitch welds would keep it cooler. good luck.

 

[Treblig]

You can use almost any method but if they don't butt together perfectly it's a little more tedious. Especially if the pipes are coming from different directions (not perfectly aligned). I usually get a very short piece of exhaust pipe that just fits over the both ends that way I get a good solid weld, but that's just me.

Treblig

 

[RustyRatRod]

The proper method is not to butt them together at all, but to leave a very small space and fill that in with weld. Overlapping pipes require a different method.

 

[cudascott]

Rustys right when butt welding two pieces together you leave a gap the size of the wire or stick your welding with

 

[kent spaulding]

PORCUPINE CITY if you try that (GAP) with a wire feed brother! You'll leave all kinds of wire on your I.D. if not proficient in the technique? You could use a gap and some filler wire with wire feed, tacking every so often and coming back into it for just short runs? I love to slam them up TIGHT and run a TIG pass at a low enough amperage as to not key hole the joint. Use some GTAW 1/16" filler wire or grab some .035 GMAW just to get you through your starts and possibly stops. You don't need a Gorilla weld to join exhaust as long as it is not under strain! Meaning hung well with rubber isolators as needed. Nothing takes the beauty away from a nice exhaust system more than some Sheoty and unneccessary Gorilla Beads!

 

[torkflight]

do not leave a gap, that will turn out awful, that is just horrible advice, if I butt weld exhaust I tig it, if not tig welding it I expand the tube so it fits over the other and mig it, that is the cleanest way to do it, like said above, nothing looks worse than shotty welding on nice exhaust.

 

[mopowers]

Thanks for the input, guys. I did one side yesterday after work. Hopefully I can get the other side done tonight. I ended up just butt welding them by stitching together overlapping tacks to keep the heat down. Turned out fine.

Follow-up question. The tubing I'm use is aluminized steel. What paint works best for spraying the welds so they don't rust?

 

[jamesdart]

just but it tight together, run it hot, and run a fast continuous bead. you get full penetration but you have to run fast enough to not blow through. ive built a ton of exhaust from u bends. works great. I have used the vht spray, and some stuff in a can from eastwood, over time they both bleed through and eventually rust but just hit it with a scotchbrite or wire brush and touch it up as needed. it will last a long time. even if you don't paint them, the weld will take forever to rust out.

 

[RustyRatRod]

Leaving a gap is the correct method for butt welding with a mig. If you have trouble doing it that way, you're doing something wrong.

 

[famous bob]

Leaving a gap is the correct method for butt welding with a mig. If you have trouble doing it that way, you're doing something wrong.

I`m no professional welder, but:
I did it the way james said, only had minor burn thru a couple of times. put a good bead w/ good penetration on it, ground the welds a little for looks, painted the whole 31/2" exhaust system w/ high heat flat black. don`t look too bad , even if I do say so myself! did eventually wrap the whole thing since I wrapped the used headers after straightening up some beat up(flattened tubes)-sure cut down on the floor pan heat-------bob

 

[barbee6043]

another thing to consider as you said you were using some of the old pipe. mig likes very clean metal, and that older pipe if has rusted is thinner making this harder too. be sure to clean the old pipe real good. .

 

[69MOPE]

I use short overlapping U tacks, jumping from one side to the other, pulling the weld, upside down U (like an arch), waiting 3 seconds between each, moving the puddle very quick over the joint line, no gap. I do not knock down the bead after, for better looks. I leave it ugly for strength.