Exhaust manifold repair

[Modern Garage]

I'm rebuilding the engine in my wife's '78 MG Midget and found this cracked manifold during disassembly. I see no soot around the crack so I presume it only leaked a little cold and little to none when hot and expanded, but nevertheless it needs repair. These manifolds are NLA new and not common used so I expect it's time to learn something new.
After a career in auto repair I can weld and braze acceptably well so my question is which is the best choice for this application. I'm planning to vee it out with a Dremel, and the owner is away for work for a while so she won't know that I'm going to preheat it in the kitchen oven. I have Oxy-Acetylene, stick, MIG, even TIG in the garage so my options are open. I'm thinking the stick (in my hands) would be too clumsy and I have almost no time with the TIG (I can't stop myself from drawing the TIG gun in and out to control heat like I do with the O/A torch) so either MIG or braze. I'm leaning toward brazing to lessen the heat input and hopefully the chance of future cracking but wanted to ask if someone with more experience in this situation could point me in the right direction.
Joe

 

[whateg01]

Welding cast iron should be done with high nickel rod. It's my understanding that it has roughly the same coefficient of expansion as the cast iron. I've brazed cast iron before but never had much luck welding. left free to move, you might need to remachine to make it flat again.

 

[Ohmthis]

Is matching the cast iron important to you? I would do one of three things based on the physical appearance. 1. Tig weld it with high nickel or stainless filler 2. Braze it with silicon bronze or brass and have it powder coated cast iron. 3. Braze it like above and leave it as is. The brazing can be done with oxy/acetylene or Tig.

 

[corn chip]

sounds like you have one shot to get it right. complete guide for cast iron welding https://www.twi-global.com/technica...lding may be used,melting point of the filler.

 

[jsaw]

Question , would brazing be able to withstand the heat that a manifold is subject to? If I remember correctly, when brazing, you heat the base metal to cherry red? I have seen a lot of exhaust manifolds get to glowing close to cherry red on an engine is run hard. If you run a small engine at night the muffler is dull red hot.

 

[The Cobbler]

Keith Rucker on you tube does a lot of cast brazing. he feels it is better than tig welding because the cast doesn't get as hot
he v's out all of the cast and fills with braze. might watch some of his videos on it.

 

[Jagmandave]

Buy a header?

I'll bet if you ask on the MG forum you'll find someone with one they took off that's been sitting in the garage for ever they would like to get rid of.

www.mgexp.com

 

[kaymccampbell]

80 bucks gets you a 2lb roll of nickel 55 wire on Crapazon. I've never had nickel 55 let me down.

 

[joe_padavano]

There appear to be several on ebay.

 

[dogdog]

Just search for ER-Ni 99 or ER-NI 55 on eBay give you some blue demon or NOS for about $40 to $70 for 1LB this price is just doubled recent months it was 50% less few months ago, not sure why.

 

[Bill T]

All of the Nickel is going towards EV batteries.

 

[Bondo]

and the owner is away for work for a while so she won't know that I'm going to preheat it in the kitchen oven.

Ayuh,..... I once repaired an exhaust manifold, usin' my bbq grill,.....

Put the manifold on the bbq, 'n lit it up,.....
1/2 hour later, opened the hood, stick welded 1/2", with 99% nickle, closed the hood, 'n left it for another 1/2 hour, then repeated til the job was done,.....
Left it on the grill for another 1/2 hour, then turned the grill off, 'n left it alone til cold,.....
The owner said it held til he sold the boat some years later,.....

Rebuilt a potbelly wood stove,..... welded it 1/4" at a time,.... took 2 weeks of very slow weldin',....
1/4", let it cool,... 1/4", let it cool,...
As far as I know, it's still in service,.... again, 99% nickle stick welded,....

 

[dogdog]

I have heard er309 and er312 or ERCUSI also works, but my turbo project never matured so can’t tell you yeah or nay.

 

[Ohmthis]

I have heard er309 and er312 or ERCUSI also works, but my turbo project never matured so can’t tell you yeah or nay.

I used 309 and Tig welded a crack in a vise I was given years ago. I did the same as above. I put it on the grill and heated it up. Got my welder set up and an air hammer to peen it. Once heated, I welded about 1/2”-3/4” and peened it with the air hammer. Then welded and peened until done. I then shut the grill off and let it cool. I still use the vise.

 

[Chilliwack Murray]

Repaired the exhaust manifold (my father-in-law actually) on my 89 ****** that came off in 3 pieces around 300,000km, probably due to the large puddle on the freeway offramp I had to go through for years. It held together with no leaks for at least another 160,000km. It can be done if you can find an old machinist/welder (like my FIL)... It's all about getting it hot, and then getting it cooled back down slowly and evenly.

 

[dogdog]

I used 309 and Tig welded a crack in a vise I was given years ago. I did the same as above. I put it on the grill and heated it up. Got my welder set up and an air hammer to peen it. Once heated, I welded about 1/2”-3/4” and peened it with the air hammer. Then welded and peened until done. I then shut the grill off and let it cool. I still use the vise.

Yes that was what I have read from various posts, and collected a lots of lbs of 309 312 and 320 rods lol ocd. Over 100lbs now I think. Just the project never mature.

As for the op, there are plenty of YouTube well known welder, fabricators that did the example fix with ERCUSI Jody from welding tips and tricks as well as weld com with ni99, and that other machinist guy don’t remember name, just don’t forget to drill the stop gap. And v groove. Preheat and post heat.

 

[OutlawDrifter]

High nickel rod for sure. Pre-heat, post-heat, and peen to relieve stress. Then find some way to insulate it to slow the cooling process.

 

[RPH]

To slowly cool cast iron after the repair heat a container large enough to totally cover the manifold. Use sand that has been heated to 300-400*F. The more the better. Place manifold in the bed of hot sand and cover with more hot sand.
Let the sand cool slowly. It’s better if you can hold the temperature over a period of hours. But it will work to slowly cool it off.

 

[Modern Garage]

Coming back to this finally to close the circle.
The more I thought about it the more it seemed the least heat would be the best option, so I decided to go with brazing rather than arc welding. After heating the manifold and a pan of bricks in the kitchen oven for a couple of hours I used the Oxy-Acetylene torch to braze in the previously vee'd crack with common flux-coated rod, then piled the hot bricks over it and returned the whole mess to the hot oven and turned it off. Five or six hours later I wire brushed the cooled manifold and ran a file over the gasket surfaces to be sure everything was flat.
After 250 miles of random driving (including extended engine overheating due to a series of mis-manufactured head gaskets - another long story) I'm ready to declare success. The engine is quieter than ever and I can see no sign of a crack re-occurring. I didn't know if the low temp brazing rod would be sufficient for exhaust manifold application but (on a simple street engine) it's working just fine.
Hope this helps anyone else looking to do the same repair.
Joe

 

[The Cobbler]

^^^ great news, thanks for the update

 

[Jim greengo]

Welding cast iron should be done with high nickel rod. It's my understanding that it has roughly the same coefficient of expansion as the cast iron. I've brazed cast iron before but never had much luck welding. left free to move, you might need to remachine to make it flat again.

I was always told nickel rod with the Flux knocked off was the hot ticket for welding cast.
I'd drill a hole inthe end of crack to stop it from spreading before welding it.

 

[Modern Garage]

Nickel rod may be a better choice for something more stressed but there was plenty of surface area after grinding out the vee and nothing else to support. No need to drill anywhere, you can see in the photos the crack was all the way around and only stopped at the web rib on the bottom of the runner.
Joe

 

[Hellpig]

A " few years ago" had a cracked exhaust manifold on my 67 Camaro. Old guy told me to Vee it out, heat it up, and braze it with a coat hanger. ( all we had was a OXY-ACET rig and a Lincoln stick)

Worked well.enough, held until I could afford headers, lol. At $3/hr, took a while to save $59.99...


And for the kids out there, DON'T TRY THIS AT HOME: coat hangers used to be metal, lol

ETA
OP, thanks for the update, I always like to get closure!

 

[laser3kw]

Great news!
just plugging a crack / non-structural, braze is just fine. Heat of the manifold won't bother it.

 

[cannuck]

Shucks, I would have used this as an excuse to build a full new system with tubular headers.

If doing braze repair, suggest use of Eutectic 16FC or any equivalent high nickel brazing rod. These alloys used to make motorcycle frames back in Olde Englishe tymes.

 

[Walkers]

I'm rebuilding the engine in my wife's '78 MG Midget and found this cracked manifold during disassembly. I see no soot around the crack so I presume it only leaked a little cold and little to none when hot and expanded, but nevertheless it needs repair. These manifolds are NLA new and not common used so I expect it's time to learn something new.
After a career in auto repair I can weld and braze acceptably well so my question is which is the best choice for this application. I'm planning to vee it out with a Dremel, and the owner is away for work for a while so she won't know that I'm going to preheat it in the kitchen oven. I have Oxy-Acetylene, stick, MIG, even TIG in the garage so my options are open. I'm thinking the stick (in my hands) would be too clumsy and I have almost no time with the TIG (I can't stop myself from drawing the TIG gun in and out to control heat like I do with the O/A torch) so either MIG or braze. I'm leaning toward brazing to lessen the heat input and hopefully the chance of future cracking but wanted to ask if someone with more experience in this situation could point me in the right direction.
Joe

You are likely to do more damage than good if you are not experienced. For one repair just farm it out or buy another one.