Toilet flange replacement

Two issues in basement bathrm (on concrete floor) of newly purchased 6-yr old home:
1. Toilet rocking back & forth.
2. Ceramic tile to be laid.

Tightening the bolts did nothing to fix the rocking problem. Since we were going to lay new tile in the bathroom anyway, we removed the toilet to try to isolate the cause of the rocking. We've found that the floor is uneven & the flange badly cracked. We've removed the bolts fastening the flange to the concrete floor & discovered the flange cannot be removed from the PVC drain pipe it's attached to (we tried). Is the only option to cut the old flange off? If so, what type of saw should be used? Also, what's the best way to attach a new flange? (For example, can we glue a 4x3 PVC flange into the old 4" drain pipe?) Your help is greatly appreciated.

Partial answer...if your floor is not flat, shim the toilet so it does not rock. They sell special plastic shims for this in most hardware and plumbing stores. Since when you tile the floor, you will raise it, that is a good opportunity to replace the flange. Tile under the rim of the new flange (it is easier to notch the tile so you don't have to drill through the tile). The new flange should be flat on the finished floor and anchored to it. If it is a 4" pipe and the existing flange is on the outside of the pipe, you could probably break off the rim, put down the new floor, then insert a new flange inside of the drain pipe. If it is mounted inside the pipe, you might need to drill it out first. One of the pros will offer their insights and experience. My unprofessional opinion.

replace 3" closet flange

thanks for the reply.

so we'll cut the existing flange off at the current concrete floor level then tile around the existing drain pipe. its is actually a 3" drain pipe. the flange was glued to the outside of the drain pipe.

we'll notch the tile in order to install the tapcon screws into the concrete floor below the tile.

i see that there are flanges that can go inside a 3" drain and they are legal. just have to make sure that the neck on the new flange is long enough to sit on top of the tile and reach inside the drain pipe.

i don't forsee any sealing problems.

Flange

Not being able to eyeball the conditions, consider leaving the glued flange where it is and get (I normally don't like them) a wax ring with a horn. Work the wax with your hands under the flange of the horn. If you are only adding about a 1/2" to the floor thickness, this seems better than reducing the o.d. of the closet stub.......

wax ring with horn

thanks for the tip.

we need to replaced the flange as it was broken and it was fastened to the concrete with only one screw. the other had stripped out. i would think it should have been held to the floor with three screws. i appreciate the concern regarding narrowing the orifice. may result in more clogging.