The good news is I got the iron flange off okay. I bought an ABS insert flange at Lowe’s – they didn’t have the kind with adjustment screws to expand the gasket, on this one the plastic insert is threaded with a tapered thread and the rubber gasket has matching thread and screws on the flange like a nut. The gasket expands as you rotate the flange & the gasket runs up the tapered threads. I think it will work okay except I ran into another snag.
The top surface of the old iron flange was flush with the top of the pipe and it was about the right height to fasten to the floor. The new flange sits higher because it cannot be flush with the pipe – it will leave about a 1/2 inch gap between the floor/flange mating surfaces. If I shim the gap I think the throne becomes a rocking chair. We’re doing vinyl floor, not tile. As far as a I can figure the most practical solution is to add another 1/2 inch layer of subfloor so as to raise the whole toilet up relative to the pipe. I think that will allow the flange to fasten to floor and not be too high for the toilet. This must be a common issue with these things. Do you see any better solution or any downside to mine?