I need to place an O2 sensor in my exhaust manifold. My exhaust manifold is cast iron and I cannot weld a bung on to it. I've also looked around and the shops around me aren't able to weld onto cast iron as well.
I noticed there is a flat spot on the manifold near the flange to the y-pipe, that would be an ideal location for a sensor. I'm wondering if it would be possible to drill and tap an 18mm x 1.5 threaded hole this spot. Is it possible to drill & tap a cast iron manifold easily, and are there any special precautions I would need to take to prevent damaging the manifold?
Are there any other options for getting an O2 sensor that I have that I'm overlooking?