Welding exhaust crack while motor running??

[shackwrrr]

I work at an exhaust shop and we have never seen a fried module from welding on a car. If you ground it right there are no issues. I will say that I have seen cars with bad ECU's from an exhaust shop using the O2 sensor as a ground clamp location, but where I work we are smart enough not to do that. Also we have tried welding with the car running but if you are trying to close a hole it starts making molten metal bubbles and you end up with a pile of permeable slag that is impossible to seal.

[black86glhs]

2 words....... tig glue.

[moparman76_69]

stop being a cheapass, get some loonies and some toonies and a few of those funny monopoly bills and pay someone to do it right.

[RoadWarrior222]

I've played that game of roulette before... it tends to make me determined to do it myself, even if the tools to do so cost more than paying a random wrench monkey to screw it up.

---------- Post added at 03:47 PM ---------- Previous post was at 03:39 PM ----------

I'm probably not gonna try it with the motor running, can't see an angle where my knuckles won't be brushing plug wires. Another daft question though, if I screw a spark plug or dead O2 sensor in the bung hole, do you think I'll weld it in, if I connect the ground clip to it... just there's not a whole lot to grab onto on the header, can't grab the flange now, it's against the motor, had to use short studs to get fully threaded ones, (Flange slightly thinner than blank part on reg studs) so there's not a lot sticking out there. The further away I go, the more chance of the current going somewhere it shouldn't. So best place to ground seems the O2 boss itself, so could screw something in to get a nut to hold onto, but haven't got any M18x1.5 regular bolts.

[3.0 van gogh]

yeah slime up an old spark plug with some grease or anti seize. Find a flux core mig machine either at harbor freight or a pawn shop. (they done cost too much) practice on the same thickness metal til you get the heat right. A little preheat wouldn't hurt (run the engine). the good thing about the flux core mig is that it doesn't have a shielding cup to get in the way and is not affected by wind and it doesn't mind a bit of dirt/grease/rust. Now, stitch the crack up. (short weld "bursts"). You will find that you can get into some fairly cramped spaces with the flux core mig gun because of the lack of the gas cup. I weld up exhaust all the time AND actually fill up holes with the flux core but I have too much experience at welding. the short bursts prevent the "weld through" or the "hole through" . remember to clean out the thread holes of the anti seize or grease with some brake clean.

[moparman76_69]

Is it cast iron? If so you need a high nickel rod, preheat, and slow cool.

[Force Fed Mopar]

I believe he mentioned in another thread that it is a factory 1st Gen Escort GT header modded to fit his 2nd Gen. If so, it should be mild steel I think.

[RoadWarrior222]

Yah, good memory, should be mild steel, can't tell what that boss is though, since it was all lightly scaled from age, so can't tell from finish if it was machined from bar or cast and machined. Think I was seeing forked sparks when I was trying to clean it up with the grinder last time, but that could have been off the previous weld rather than the boss itself.


Dunno if a MIG purchase is doable right now, well fairly certain it isn't for a month, but I do have a lot of bodywork to do...

[Force Fed Mopar]

It will all be steel, they didn't mix and match cast and steel.

[moparman76_69]

FWIW I've brazed exhaust manifolds several times and never had an issue. They were all cast though.

[RoadWarrior222]

Yeah, probably not, though it does make me wonder why it blows loud when I first start it and "seals up" as it gets hot, that's why I missed the crack at first glance a week back, looked when it was hot.

---------- Post added at 10:11 PM ---------- Previous post was at 10:08 PM ----------

BTW what's surprising me, is that this header, with a coat of "ceramic" rattlecan exhaust paint on, seems to be running cooler externally than the cast mani did with a heatshield over it. At least it's not trying to melt the cheapy wiring loom I tried to protect plug wires with, which the cast mani did.

[black86glhs]

Cast iron is a heat sink so that is probably why it did that. That is why radiators were made from it(house ones).

[wallace]

FWIW I've brazed exhaust manifolds several times and never had an issue. They were all cast though.

I've had good results with brazing thin material for exhaust. I had a 400cc 2 stroke dirt bike back in the day and the expansion chamber cracked all over. I brazed it up and when I finally got all of the cracks done I think there was more braze than metal but I had no issues with it and that bike was one "buzzy" machine everything on it had to be loctited.

[RoadWarrior222]

Hmmmkay, well I've wimped out for now...

Half my problem with this car is I only get to attack it an hour or two at a time. I thought I was gonna get all day on it, but had to wait around for a phone call this morning. Then by the time I could get out of the house, it didn't leave much time for finding supplies... well I thought 3/32 rods are straining my welder to the limit, so was looking for smaller, but could only find 5/64 and 1/16 in big packs, and 6013 instead of 6011, was one place I remember having 5 or 10 rod "try it and see" packs, which I thought was what I was gonna do, but of course they don't have them now... having a tight cash period again, or I might have just bought the 5lbs.

Which might be just as well, either the crack spread since I last looked or I didn't see it had gone right round last time. And there would have been no doing it in situ anyway.

Anyway, came home with a pack of HiTempSteel stuff, which seems the same as ThermoSteel, and glooped that all round and crossed my fingers.... Few people online say it's held on cast manis for months/years. But, I am not hoping too much, think it needs more mechanical strength for where it is. Stuff seems like fancy muffler cement.

Well after getting under the front of the car to glob it well round underneath, I did a , coz it might not have been my weld that gave first... Saw that the mounting bracket at the end of the header broke off, so it's been getting mechanical stresses it shouldn't have. Well/so it's gonna have to come off and get seen to properly, I might put extra straps between the secondaries while I'm at it, try to stop them moving much in relation to each other.

You might be wondering why I'm stalling, well, a lot has to come out, to get the header out.

I'm wondering what's going wrong though, I broke that same bracket on the last stock downpipe and the converter (In the DP) started to get a stress crack. I checked the engine mounts when I put this in and they're all lined up correctly and they're newer than the car, maybe 8-10 years old, not cracked up compressed stock rubber anyway, but seemed in decent shape. There's a decent amount of material in them too, same "bulk" as the TM ones by eyeball. Get enough friggin' vibration too, so they have to be pretty firm. Have to go looking at the good mazda mounts I guess, or immobilise the sucker with a bobble strut or something. (I swear I manage to break/stress parts nobody else does)

[85boostbox]

No my bracket on my exhaust has done the same thing on my 93. I am thinking of installing a longer exhaust pipe.

[BadAssPerformance]

crappy design, seen/heard many cracked

[RoadWarrior222]

Hmmm, got a feeling it's the mazda platform with ford motor cobbled in that must be the engineering disconnect, the mazda motor seems to offset the DP. Guess I'll have to lie there and stare at it for a bit. (i.e. construct 3d model of problem in head and "software" test some solutions, before rejecting all of them as complex and/or expensive and fixing it with duct tape.)

So let the goop set up as directed, and then drove it around gently this evening, sounds a lot quieter, not sure I got 100% of the crack, but didn't wanna stab the pedal and find out, when I thought it might blow it off. After it's done a couple of highway burns, I'll check it again. Think I can "touch it up" still have a small blob left.

I am having a bit of a laugh looking round some welding websites. One guy is saying, "don't learn arc on anything smaller than a 1/8 rod" another is saying "stay below 3/32 rods until you get the hang of it", then there's the welder buying guide, which basically says, "Don't bother with X when Y is just $100 more"... up the entire range...so I guess I'm looking for a 3/4 ton truck to pull a 10kW diesel welder/generator.

[3.0 van gogh]

well, I guess if I had your dilemma I would choose the 6011 rod. This is what I like to call the "junk yard rod." It is somewhat easier to use for the beginner and it doesn't mind a bit of rust/dirt. Ive welded in floor pan patches with the 6011. The 3/32 rod size should be perfect although don't expect to make a "pretty" weld with it. The 6013 rod is just a bit harder to use and it doesn't like dirt as much. Mostly it is used for sheet metal and in the right hands, is a great rod. Like I said earlier, if you are worried about burn through, just make short lengths of weld, this prevents the metal from getting too hot. Yes, have the amps cranked up a bit but don't try to make the entire weld in one shot. Arc welding on thin metal can be done but you will burn through before you know it if not careful. Another option if you do remove the header could be 7014 rod. It is a low penetration rod/high build rod but it doesn't like to be welded in vertical or horizontal positions. Makes a pretty weld and is very easy to use.

---------- Post added 01-28-2013 at 12:03 AM ---------- Previous post was 01-27-2013 at 11:59 PM ----------

109.99 Harbor freight flux core wire feed welder

[RoadWarrior222]

Don't have a HF in range, cheapest around here is about $200

I'm not actually sure that most MIG guns aren't gonna be too fat, I've got about 3/4" between the 2 secondary pipes.