I have a hairline crack in the MR2's cast exhaust header. I have a replacement that I am swapping in over the winter, but what to do with the old one? Can cast iron be welded?
I am too lazy to Google it. Nothing I would try to repair, just something to practice on.
In theory, yes, but I think it would be brittle. Of course, the base material is, too
http://www.lincolnelectric.com/en-us/support/welding-how-to/Pages/welding-cast-iron-detail.aspx
Cast iron is difficult, but not impossible, to weld. In most cases, welding on cast iron involves repairs to castings, not joining casting to other members. The repairs may be made in the foundry where the castings are produced, or may be made to repair casting defects that are discovered after the part is machined. Mis-machined cast iron parts may require repair welding, such as when holes are drilled in the wrong location. Frequently, broken cast iron parts are repaired by welding. Broken cast iron parts are not unusual, given the brittle nature of most cast iron.
There's lots of HOW-TO on that page. This is the depressing bit that is relevant to you
Sealing Cracks Because of the nature of cast iron, tiny cracks tend to appear next to the weld even when good procedures are followed. If the casting must be water tight, this can be a problem. However, leaking can usually be eliminated with some sort of sealing compound or they may rust shut very soon after being returned to service.
So, yes, your crack could be fixed....but contraction of the weld site during cooling could cause a crack. Can you fit it in an oven? You might be able to pre-heat/post-heat to slow the cooling process.
Yeah, it's all about slowly heating it up and slowly cooling it back down so it doesn't crack.
weld it with the car running and let it idle before shutting it off!
I know it sounds stupid, but it would probably have your preheat and postheat covered.
JoeyM wrote: ... or they may rust shut very soon after being returned to service.
LOL ,wow. That's classic. "Ehhh, don't worry about it ma'am. It'll just rust itself shut."
Taiden wrote: weld it with the car running and let it idle before shutting it off! I know it sounds stupid, but it would probably have your preheat and postheat covered.
I wouldn't weld on a running car! bad things can happen to the electronics. you should unhook the battery when welding just to be safe.
BUT, running it to hot, dropping the battery leads, welding, then reconnecting and running to cool sounds like a pretty dang good idea.
Taiden wrote: weld it with the car running and let it idle before shutting it off! I know it sounds stupid, but it would probably have your preheat and postheat covered.
Maybe that would work with oxywelding....I would be chicken to do that with any form of electrical welding setup...new ECUs are not cheap.
I have sucessfully welded cast iron includung engine blocks a number of times. As was noted, preheating and slowing the cooling are important. I also have a large vise that I welded 20 years ago and use it on a nearly daily basis. The welding was done with a Linclon 225 welder and nickel rod.
Is this the answer?
JB Weld
Taiden wrote: weld it with the car running and let it idle before shutting it off! I know it sounds stupid, but it would probably have your preheat and postheat covered.
Generally speaking , if you don't fuse the entire crack, it will reappear in time. It'd be hard to get full penetration with the thing attached.
There's a lot of mass in an exhaust manifold. You may want to pre-heat in an oven to 500 or so. It'll hold temperature for a while.
In reply to jrw1621:
That's the antiMiata... J-B Weld, like violence, is almost never the answer.
Short answer is yes it can.
A good friend of mine (now deceased) who used to restore cars and had a rare Bentley in his shop. He was supposed to just get the car running. Seems the car had been in storage in a barn in Evergreen SC for years. When it finally sold, the owner wouldn't let the buyer look under the hood (or so the story was told). When it was finally purchased, you guessed it, cracks in the cylinder head from storing with water/no anitifreeze. Firend paid some high dollar welding shop to repair it. Didn't work. They brought it home and fixed it themselves. I do know they heated it before welding. They also ended up doing a complete restoration on the car that took years. The car looked good when they got it, but they said it was rotten underneath.
Pre heat, as mentioned, wrap it or put it in the oven and slowly cool it down afterwards. Other key is using a Nickle rod in a stick welder. Also peen the weld while hot, a little more than just chipping the slag away.
Have had scucess on large cast compressor pulley/flywheels with the above method.
pinchvalve wrote: I have a hairline crack in the MR2's cast exhaust header.
You should drill a small hole at each end of the crack to keep it from growing. 1/16" will do it, then fill the hole in when you weld.
Dan
bigdaddylee82 wrote: Pre heat, as mentioned, wrap it or put it in the oven and slowly cool it down afterwards. Other key is using a Nickle rod in a stick welder. Also peen the weld while hot, a little more than just chipping the slag away. Have had scucess on large cast compressor pulley/flywheels with the above method. - Lee
I welded a panhard bracket using this method, use a torch to preheat, when it is glowing go ahead and stick weld it using nickel rods. Then as it cools slow it down by reheating a little with the torch a couple of times around the welded area.
I had no problem with this weld with 500 horsepower.
In our shop, after welding cast iron, they use vermiculite to insulate the piece while it cools.
I did the same on the rear for the MG. Lots of torch fun and a nickel rod. See if you can find out what kind of cast it is, too. Some are easier than others.
And don't be too lazy to Google, for the love of God.
I've welded cast iron numerous times with one of the various rods from Lincoln (sold by Tractor Supply). It's easy to do, and no problems with cracking.
914Driver wrote:pinchvalve wrote: I have a hairline crack in the MR2's cast exhaust header.You should drill a small hole at each end of the crack to keep it from growing. 1/16" will do it, then fill the hole in when you weld. Dan
This little bit of info is absolutely key.
I prefer to gas weld cast iron and have even brazed cast iron successfully. Pre & post heat etc., Yada, Yada, yada.
As others have said, drill holes at each end of the crack, preheat, weld (nickle rod), post heat, cool down slow. I welded up 4 or 5 cracks in my Esprit manifold doing that and they all held. It cracked next to the weld. I should have post heated it more, like with a rose bud torch, then stuck it back in the oven at 500 for a few hours and let it cool. Anyway, I've also welded cast iron with 6011 rod and it worked, but it wasn't a turbo exhaust manifold made in England with a poor design, poor materials and poor manufacturing.
what i've always read...
drill crack ends, cut a V into the crack where you'll be welding (every time we read about welding in GRM its all about prep isn't it? lol)
then preheat... i've read tossing it into the oven at highest temp or tossing it on the gas grill... weld with high NI rod, toss back in oven/grill and allow to cool slowly
If the weld is not stuctual as in holding two pieces together and more of a filling operation you might try brazing with a bronze brazing rod which has a flux. All the other ecomendations apply such as stop drilling the ends of the crack and preheating.
Because the bronze is more ductile then the cast iron braze might last longer with less chance of cracking again in the same place. Brazing with bronze rod is actually more similar to soldering then melting the parent metals together.
If it's not red hot and glowing, it's not preheated. And you can't get that kind of temperature from a household oven. Localized heating like that with a torch just creates new cracks around the area.
This is why I'm far from enthralled with the notion of preheating iron for the home welder. Heck, even for most welding shops. They don't have the ovens either.
Weld cold instead. As in room temperature. It works quite well, especially with something like a ferro rod. Which is what you usually want for an exhaust manifold because of the contamination.
Don't run a long bead, do it in a series of short stitches. Just like you would thin sheet metal. Start the beads at the ends and you capture the crack in the puddle. This negates the need to drill.
No, this isn't 100% perfect at all times under all conditions. Yes, real preheating is better. But, it works quite well almost all of the time when the average welder is fixing cast iron.
I've done some.
Preheat for an hour to 500 degrees in the oven.
Weld quickly allowing it to cool as little as possible.
Put back in 500 degree oven for another hour.
Turn oven off, but leave the part in it and the door closed.
Come back the next day to a cold and welded part.
Also - I have had some success welding one bead down on half of the crack, another parallel bead down the other half of the crack, and then a third bead to connect the first two. The first two get to get a good bite into the base metal without being subjected to the cooling stress, and then the third bead, you're mostly just welding to filler, not to cast iron any more. Finally - a convex weld puts less surface tension into the part than a concave weld, so pile the filler on.
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