Recently bought a fixer upper and there is a crack running through most of the 5 foot section of the main stack. It is 4" cast iron. I am planning on using snap cutters to remove the pipe, but I don't have a way to properly secure the stack above the cut.

The area is too small for riser clamps. I bought some but could not fit them around the pipe. The only way to use them would be to completely change the way the walls are in the bathroom. There is maybe 5 feet of cast iron pipe above the section I am cutting out.

Any help on how to do this without damaging the stack above the cut would be appreciated. If photos help, I can go take some.

Thank you.

If it is only 5 ft. you can have someone hold the upper pipe, at least until you can get a piece of PVC in. If it is a vent line also, and you have an attic, you might be able to clamp it there. Good luck. Make sure you put the Fernco fittings, or whatever you are using, on the pipe before replacing.

Vent stacks can weight hundreds, thousand of pounds so please tell us how much pipe is above the cracked section. Safest, best mthod is to remove old stach from above the roof working down to the cracker section. Replace with PVC from there on up through the roof. PVC is cheap and not hard to install.

There is many ways to support it. See the pic below for one of those ideas...

If you don't want to cut ceiling to support Riser Clamp as shown in the picture than attach Riser Clamp below the ceiling and onto the pipe, support both ends of the clamp with 2" x 4"s and cut...

I put that about 5 feet of CI is above the section I need to cut out.