Radiator Doesn't Quite Fit Valve
Recently a valve on one of our radiators cracked and began leaking steam. So I tracked down a pipe wrench and a 5' length of pipe for leverage and was able to detach the radiator from the valve, and the valve from the pipe. The 1 1/4 replacement valve from the hardware store fits the pipe perfectly, but doesn't quite match up with the radiator. The threading is on the valve side, and there is a threaded collar on the radiator—it is just slightly too big to tighten onto the valve (about halfway through tightening it sort of pops and loosens).
The valve came with a new collar, but I am entirely unable to detach the old collar from the radiator. It doesn't seem to be a part of the radiator, but even with 5' of leverage I'm entirely unable to budge it.
My makeshift solution was to build up enough teflon tape on the valve side and tighten that way. Honestly, it worked alright for about 2 cycles of the radiator and then began leaking a bit.
The radiator is from the 20s and replacing it isn't really an option. Is there an adaptor I can use to step down? Some other type of tape possible? I have a micrometer, so I can measure accurately if necessary.