Welding exhaust manifold

[toadshade]

This is an expansion on a previous thread:

I just removed the exhaust heat shield and discovered a small crack in the manifold. I am a welder so I am not worried about welding the cast iron even though I know it could suck. But I wanted to get an opinion on welding it while still on the engine. The crack does not extend to the edge of the manifold and is so small, there was no noise and just the smallest black spot where it was leaking through. Is this something that is just a bad idea to attempt while still attached, or is it worth a shot? Is there any risk to doing it this way? I guess I have read too many nightmares on removing the rusted manifolds. But at the same time, it would be a peace of mind since I need to install a pyrometer and was the whole reason I took the heat shield off in the first place.

 

[mudgudgeon]

Whats the process for successfully welding cast iron?

 

[toadshade]

10 people will tell you ten ways. But I have done it two ways. TIG weld with Monel or Inconel (high nickel alloy rods) after pre-heating, then insulate with kaowool ceramic blanket until cool. Or stick weld with cast iron welding rod, ball peen to relieve stress and then insulate with kaowool or sand bath. Either way taking it off would be best. But if I can insulate it on the truck, I might be able to pull it off. Biggest problem is that I should drill out both ends of the crack first. That is my biggest concern.

But is this thing guaranteed to get worse? The stress is now relieved in the cast iron. There is no sizeable leak. Like I said, I did not even know it was there until I took the heat shield off. Do I want to fix it, yes. But am I leaving a problem unfixed that will cause a problem later? I do realize in the time it took to write this I could have had the freaking manifold off.

 

[mudgudgeon]

I do realize in the time it took to write this I could hav

You haven't removed many manifolds have you


Sounds like it would be worth the effort to remove it

 

[toadshade]

Ugh. I have not. Never took one off. But I know it is just what needs to be done. BTW, since I have it off, is it better to repair or replace? My experience with all metals is that a welded area creates stress on the welded area. If the cast iron is already this prone to cracking, I would think there would always be tendency to crack at or near the repair. Does anyone have experience that would say that is the case? I know there will always be a chance that the crack opens back up. More than anything due to an improper weld, but what about nearby? For about $300 I could get a new manifold. If it means I might not have to replace/repair it again for another 25 years, is it a worthwhile investment? But if a repair is satisfactory, then I will save the money. Just don't want to take it off just to have it crack again. I will risk my ability to weld it.

 

[tweeek]

I think you are over thinking it. Pull it, it's really not that big of a deal, how corroded are the studs? Usually hdj81 are relatively low milers. Get new studs and nuts.

Weld the crack, and drill it for the pyro while off.

I've pulled mine a couple times to deal with the turbo, it's a bit of a pain, but really not that big of a deal.

Good luck!

 

[toadshade]

I appreciate the confidence. But you are right. I am preparing to take it off. The studs and nuts are rusted, but no way to tell how bad. I will find out soon.

 

[IanB]

It's about a 7 hour job to remove and replace the exhaust manifold if everything goes smoothly. Depending on your exhaust configuration, you may find it works best to pull the front driveshaft to gain some more room to work. Big X2 on having new studs, nuts, and gaskets on hand for this job. I'd also recommend the o-ring, metal rings, and collar to rebuild the slide joint between the 2 sections of manifold as well.

Some large bolts work great to plug the turbo coolant lines with the factory clamps so you don't lose all your coolant. You'll need e-torx bits to get any stuck studs out of the head and tighten the new ones in (and for various studs in the turbo if you were changing over to another turbo). An extra set of hands is key to wrestling the turbo/manifold assembly out/in the engine bay as it's pretty heavy and you need to work around some stuff like the AC compressor and lines.

It's not a job you want to be doing every other weekend, I'd be very tempted to replace the manifold rather than repair for this reason, but I'm not a welder so you would know best if you can properly repair it. Great opportunity to drill and tap it for an EGT probe while it's off as well.

 

[toadshade]

Great advice. And yes, this all came about because I was going to install an EGT. Looks like it will also be a good time to flush the coolant. Needed to be done anyway.

 

[Sungazer]

What about cold weld aka JB weld?

 

[YoYoHo]

This may sound stupid but the way we fix them on the machines is we run the engine up to temp, turn it off , weld them, restart and get back to work, keep them running for the day.
Have always Tig welded them with Silicon bronze starting in the center of the crack and doing two fillets so the max heat is on departure and cold start is not an issue. If possible we will drill both ends but that isn't always an option.

 

[toadshade]

That is exactly what I am about to do. I was just talking with someone about doing it that way. I am going to give it a shot. Easy enough. If it works, great.