Fixing manifold crack and reinforcing
 

Built this manifold last winter. I have something like 15k on it, and 8 track days.

https://www.miataturbo.net/attachmen...ine=1444158225

Just found this crack. Ran it for a whole track day, and an 800 mile trip home with no soot coming out at all. Must not leak much. I believe it is from thermal expansion.

The plan

Drill out both ends of the crack to stop propagation.
Clean the inside very well and try and clean the actual crack (how?)
Backpurge and weld the crack.
Add a gusset between the 2.

Suggestions? What thickness plate should I use as a gusset.

Also thinking about cutting more relief cuts.

Get an air powered die grinder and some carbide burrs to clean out the crack. I'd skip drilling out the ends, and just weld it good once you've ground every bit of the old weld out. Consider welding on the inside as well if you can reach it easily. Clean the metal with acetone before welding, don't use brake cleaner or anything chlorinated unless you really want to die.

Every bit of old weld isn't coming out of that. Its a giant pile of filler. I can easily get to it from the inside. yank should be bringing over his die grinder.

I'll try and find an old picture of the weld.

Try to get through the crack at the very least. Even if your new weld is all filler, you will have a cleaner weld than before.

Ok. Will do.

I just ordered some .125" flat bar to cut as filler also.

Why would you skip the drilling?

I would drill out the ends, grind out some of the crack, and add a gusset. If it is stainless of course you should back purge when welding.

Whole manifold welded without backpurging...oops.

This time I have a second regulator, and will just use my spare bottle to backpurge.

Wired the welder into 220v last night and got the full 200amps. Still waiting on the stainless gusset and time to pull the manifold.

I don't think the drilling would really be necessary if you grind all of the crack out and a good bit beyond it. You can drill it, but you should be grinding really far down in to it anyway. The correct way to repair a cracked weld is to grind it all out until you are down to solid material. If the crack is all the way through, you will have to make many passes to build it up.

Also, preheating and post heating a weld can help stress relieve the material you are working with.

I think that broke from thermal stress on that joint. So solution is to spread the stress out (such as a gusset) or reduce the stress (cut flange between runners to allow them to move thus less stress)
Here's what I would do to fix it.

Clean, grind out, drill to stop crack.

Reweld. Then weld a gusset top and bottom to help spread the load out in that area. Then cut the flange to allow it to stretch a bit.

For gusset thickness, I would use 1/8" or so.

Its like you read my mind Pat. Its not really a load bearing joint. Has to be thermal.

I had a welding engineering class I took while I was in school. I could calculate the stress in the weld at a given temp with enough math. The worst thing about that joint is the tight radius.