Any suggestions on a leaky radiator drain? I replaced the valve with a new brass plug 1/8" npt. But even with tape, it leaks. It appears the threads have been buggered up over time. What is the best course of action - to try opening it up and tapping the next pipe thread size? Or is there something easier?
I would first 100% verify it is coming from there vs. somewhere else and traveling to that point. We all have been fooled at one time or another with the actual leak not where we see it.
You could try running a 1/8" not tap in the hole to clean it up, but don't take out to much material or you'll never be able to seal the draincock. I don't think there is enough material to go to the next size.
I agree, after verifying that's the place, run in a 1/8 NPT tap just enough to straighten the threads without digging way in. Use pipe thread compound when you install the petcock.
I think Chad meant a 1/8" NTP tap (National Taper Pipe--as apposed to a NSP, National Straight Pipe).
But I could be wrong! As he said, don't go overboard with it, I would even be tempted to do it by hand, with no wrench on the tap. It just takes a little, and the bung is brass. (or should be!)
Ooops, yes David, I did mean NPT...My phone thinks it is smarter than me sometimes.
they also are nps taps national pipe straight. i find many modern fittings are not threaded far enough back you can fix that with a die. philip
Where I have had misfitting threads I have ran a dot of solder on the threads and brushed it until it is even all around (just a film only) This has been successful on several occasions for me.
Thanks for the help. Pulled the radiator, cleaned the threads with the 1/8 npt, put in a new brass plug with a little Teflon tape, and all is good.
When tapping steel as thin as the underside of a radiator, I drill a small hole, then enlarge the hole using increasing sizes of tapered punches until the hole is slightly smaller than the starter tap. Doing it this way, the punch pushes the steel around the hole up into the radiator, so instead of tapping the thin gauge thickness of the steel, which barely has enough thickness for one or two threads, you are threading the walls of the hole that were pushed up into the radiator, which allows enough room for lots of threads to hold and seal the drain cock securely.
Henry, I would enlarge your current hole in this way and tap it to accommodate a brass reducer bushing with the inside smaller female threads the same size as the male threads on your drain cock. If you are unable to find a reducer bushing of this size, use a larger plug to plug the leaking hole and make another hole for your drain cock using the above method. Jim Patrick
PS. The hole should be just barely large enough to fit the tip of your starter tap in. If you enlarge the hole too much using the tapered punches, the threads of the tap will not cut deep enough into the upturned walls of the hole to form a good seal.
Most T radiator drains are on the lower hose casting, not in the thin brass of the bottom tank, otherwise your process does work for thin metal.
The best way, IMHO, to put threads on a thin piece of metal is to solder/braze a thread bung onto the metal.