Maybe. It all depends on how the long-gone manufacturer assembled the radiator. A cast-iron radiator goes together in sections, like a loaf of sliced bread. Each section attaches to the next with round metal fittings called nipples. Nipples looks like very short pieces of pipe, which may or may not have threads on them.
Threaded nipples are unusual in that one side has a left-hand thread, while the other side has a right-hand thread. As the manufacturer turned the nipple one way between the two sections, it pulled both sections tightly together. After a few years of normal use and corrosion, the threaded nipples and radiator sections became one, never to separate again. Because of this, threaded nipples aren’t available anymore. If you’re looking to reduce the size of one of these old beauties, you’re out of luck.
And then there are push nipples, which are still available. A push nipple is a smooth piece of pipe that’s beveled. The bevel makes the push nipple wider in the middle than it is at either end. Rather than screw the radiator sections together, the manufacturers who used push nipples pushed one section into the other, taking advantage of the nipple’s bevel to create a tight seal.
If your radiator has a threaded rod running between its sections, rest assured it has push nipples. Now all you have to do is get the beast apart. Loosen and withdraw the threaded rod. Next, apply equal parts of patience, pry bar, and elbow grease. If you’re careful and persistent you should be successful. Remove the offending section and reassemble the radiator.
If the old push nipples don’t look so good, get new ones. And don’t waste your time shopping around for these because there’s only one place you can go: Oneida County Boiler Works (Phone: 315-732-7914). Give them a call. They’ll want you to send a sample of the old nipple (no matter what condition it’s in) and they’ll take good care of you. They regularly help people from all over the country, and they assure me that Oneida is the only company around that still supplies these fittings. “If people could get ‘em any closer to home, they wouldn’t be calling us!” they say. I believe them.
Once you get the new push nipple in place, tighten the push rods, and pull the radiator sections back together. (Gosh, I make that sound so easy.)