I need a little advice. I'm making the back half of the dutra exhaust from my stock manifold. I have access to a MIG welder, and possibly an arc welder, but I've no exp. with an arc welder.

Would the MIG welder work to weld the plate onto the cast iron? This is the easiest welder for me to use and I've had a little experience with one. The other alternative would be to screw it on and braze it on with the mig welder (this is what I've done most in the past, brazing with bicycle frame lugs and tubes)

Thanks in advance!

MJ

Welding cast iron is very tricky. You will probably have to heat it in an oven to dull red, otherwise it will crack.

_________________
I've been calling it as i see it for my entire life and that's not about to change. Take it or leave it.

ok, so you think I should try the screw&braze method instead? I figured it would be easier to weld than try and tap those guys in real accurately.

Would the MIG do the trick or not get it hot enough?

MJ

well, yeah, that's another problem I forgot to mention, the manifold will suck all the welding heat away from the point of contact like a fart in the breeze, while the patch plate will retain it all, so youll probably find when you strike an arc that it will only stick to the patch. Heating the manifold will help out a lot with that, but of course the contraction once everything's cooled down might crack the welds since you are welding a steel plate on there. Yeah, doing that patch will be a PITA, Ive never done it, but many people I work with have tried welding castings and have shared their stories with me over the years. You might find a commercial welding shop that can do it for you successfully; theyre pretty industrious.

_________________
I've been calling it as i see it for my entire life and that's not about to change. Take it or leave it.

I don't now if you can use steel MIG wire welding process on cast iron. Those are completely different materials!!!!!!!

Do a websearch for "cast iron welding". You will get lots of results.

This website is pretty good... http://www.locknstitch.com/CastIronWelding.htm

Read and understand each page, then click the link at the bottom to go to the next page. When you are finished, read it through a few more times.

Here's a good site I came across a while back:

http://www.esabna.com/EUWeb/OXY_handbook/589oxy8_1.htm

D/W

_________________

If it ain't broke, fix it!

Heat it next time you have a barbeque! just put it in there...
I saw a picture from D D with that way to heat it up.
I have had good luck with mig welding cast, as long as the parts don´t see much load.
I just heat it up real good and crank up the welder as high as it goes.
(But my welder is small)
It is probably not the best way, but works.
After I finish welding, I wrap the part in insulation stuff left over from the house, to cool it slooow.

Ah the BBQ! That's an idea. If you can find that link rust let me know. I've spent some time looking and had no success.

What do you think about having the the manifold transfered from the BBQ to sand vs. home insulation. I don't have any spare fiberglass sitting around but a bag of play sand is easily had

I dont mind giving the 4 screw/braze or even hi-temp sealant approach. I appreciate all of the input and tricks. This will be an adventure, I just dont want to mess it up and have the manifold or welds crack.

MJ

I thought I read once that you need to use rods very high in nickel content for welding cast iron. It was also suggested to bury the item in sand so it cools slowly (the sand helps retain the heat).

Jerry

_________________
There's a difference between ignorance and stupidity.
Ignorance is not knowing any better.
Stupidity is knowing, yet doing it anyway.

If you can, heat the entire part up in an oven first. The problem is that the cast iron shrinks back up at a different rate than the weld, thus stessing the original metal near the weld. IF it cracks again, and it might, it cracks away from, but near the weld.

_________________
69 Dart Swinger, 230 ci slant, t-5 five speed, intercooled turbo, 4 wheel disk brakes, tubular upper control arms.

i'm no expert, but i weld a fair bit...
If the weld isn't structural, so it's only sealing the exhaust gasses, wouldn't your best bet be to bolt it for srtength, and braze the join just so it seals...

Brazing doesn't produce as much heat as actually welding (with an oxy, don't know about mig).
And yeah, cast iron is very brittle, and even moreso after you weld it... the best thing to do is heat up the entire thing while you weld it, but that may not be possible.
Second best option is probably just to make sure it cools very, very slowly.

Dunking the freshly welded material in warm oil would probably do this.

_________________
www.illwillpress.com
Foamy the Squirrell rules!

I know "nothink nothink" about welding, but I can add that my rear Dutra modified exhaust has a block off plate attached with 4 screws and no welding. I bought it from a fellow list member so its on its second car right now and shows no signs of leakage. So it is possible to take the easy road on this!

_________________
65 Dart GT Convertible
http://www.displacedkiwi.com (click on /other then the dart icon, then whatever you want!)