Radiator vents, to tap or not

nicholas bonham-carter

get a tap for that size: 1/8 npt and very LIGHTLY chase down the threads in the rad. you are only cleaning it -not cutting depper threads. it helps when starting anything in old threads to turn the piece BACKWARDS until you feel " the seat"- a sweet-spot for threads]-then you can turn in the correct direction to tighten. actually i do that with new threads as well!--nbc

ChasMan

To clean or tap new vent openings

I bought two Heat Timer Varivalves (1/8 " angle) to replace the old vents on two one pipe steam radiators. The old vents had a tapered stem to go thread into the vent port on the radiators. The Varivalves do not taper and don't quite thread. They feel like they want to cross thread.

I can't tell if the threads for the vent opening on the radiators are gunked up or just worn down at the start of the opening.

If gunked up, what could I use to clean them?
If they are worn down what are my options? If I force the Varivalves into the opening would they "cut" there own threads or would I damage the thread on the Varivalve itself?

Would I have to re-tap the vent openings and then use bushings to screw the Varivalve into? Or do something else?

Would appreciate any ideas?

Thanks