What I would do is this, there are a few ways to cut cast iron pipe, I hope you have a sawzall, if so you need to get a diamond grit blade, prefferably an 8%26quot; one, made for cutting cast iron. the pipe that rises up to the toilet flange, find a spot on it that you can access with a sawzall to cut it, it's a slow process but it will get through eventually. cut the pipe off about a foot or so below the old flange.
But make sure that you make a cut at least 6%26quot; away from any hubs. If the pipe is 4%26quot;, get a 4%26quot; x 3%26quot; Fernco (rubber) adaptor. These are used for joining 2 dissimilar types of pipe together. After this you'll need a piece of 3%26quot; pipe and a toilet flange. (If the floor is bad around the toilet this is also a good time to fix that.)
Put the Fernco adaptor on the cast iron and tighten it on with the hose clamp that comes with it. Put a piece of 3%26quot; pipe into the other end of the Fernco, long enough to go through the floor. Don't tighten it into the clamp yet, the top of this pipe should be flush with the top of the floor, if it's not cut it so it is.
Now, glue this pipe into the new toilet flange. (If you have a basement, this should be alot easier.) Put the pipe through the hole in the floor into the fernco. Measure from the back wall to the center of the toilet flange, line up the bolt slots for the flange with this measurement.
Screw the flange to the floor, use large head phillips screws. It is important to do this. Don't forget to tighten the 3%26quot; pipe into the fernco. Put the toilet back on, I assume you already know how to do this. Check for leaks, and that's it.
Good LuckHow to replace toilet flange on cast iron soil pipe?Couple of acceptable ways to just replace the flange.
1. Using a small chisel, cut all the old lead out of the old flange around the pipe. This should allow you to remove the existing flange. Purchase a new flange, caulk with oakum and pour lead and tamp with caulking iron to secure and seal. Secure new flange to floor.
2. Purchase new flange replacement that actually fits over existing cast pipe and seals securely using bolts that compress seal. Securely anchor to floor. This may require removing a little flooring material around the pipe to allow flange to fit.
2a. They also make a PVC replacement that fits inside a 4%26quot; cast iron and tightens the seal using bolts. However, you may still need to cut the cast iron pipe to get the replacement flange to fit tight against the floor. The cast iron pipe can be trimmed easily with a small angle grinder. Just watch the sparks.How to replace toilet flange on cast iron soil pipe?Go to your local plumbing supply store and tell them the problem. They make a PVC replacement for cast iron, the problem is having room to put it on. If it is a concrete floor, you are looking at busting up some concrete. If it is a conventional floor you will have a much easier job. Good luck!How to replace toilet flange on cast iron soil pipe?If you have a busted flange that isn't too badly broken out, they have repair parts for them. It is basically a curved piece of metal that slips beneath the flange and spans the broken area so you can clamp the toilet down. I had a flange break out and I got the repair part at Home Depot for just a few dollars... There ain't no easy way to change one!!! ....Good Luck...
