How do I make changes to the actual range to convert it from 3 wire to 4 wire?
Everyone talks about replacing the wiring cord with a 4 wire cord, but I have an old range that grounds the common to the frame. It seems to me that I have to disconnect the ground to frame connection and install a separate ground. Does anyone have suggestions?
Thanks.
Rich

The problem is that the range has only three terminals to connect the 4 wire harness to.
The two hot wires and a third terminal that has a combined common and ground.
The question is: How do I separate the common from the ground.
If I find where the common is grounded and then disconnect it, I can then use the third terminal for the common. I still have to attach the ground. Do I drill a hole in the case and then attach the ground using a self taping screw?
My guess is that most people just attach the common to the third terminal or attach both the common and the ground to the ranges third terminal. Both of which would appear to defeat the purpose of having a separate common and ground. Comments?

You have to pull a neutral from the fuse box, not a ground and this generally means pulling a new cable.

Ground always goes to the case.

If, indeed neutral is connected to ground in the range, it would have to be made separate.
Neutral generally is used to power the 120 portion of the range controls.

What's done in industry (not necessarily for ranges) instead of pulling a neutral is to use a 240 to 120 step down or control transformer for the 120V controls.