Still working to replace my 1926 radiator. Got the shell brackets installed, but cannot get the new petcock to screw into the lower tube. Tried the old petcock and it won't screw in either. Is there a trick here I'm missing? I don't want to bung up the threads.
Chase threads with a 1/8 NPT tap.
But do not run the tap all the way through. Pipe threads are tapered. Just run the tap in until it starts to cut.
Paul, I may be wrong here, again! I thought the female thread, the hole in the casting, was tapped parallel. The only way to have that thread tapered was to leave the hole with an incomplete thread, as you suggest. The seal comes with the tapered male thread on the petcock. as it is wound in, the threads begin to bind to make a tight seal.
Can anybody set my thinking straight for me?
Allan from down under.
Wayne, just a thought ,but did you remove the plastic plug ?
Both male and female pipe threads are tapered. Look carefully at this picture of a 1/4 pipe tap and nipple and you can see it.
Well.... I said 1/4 but you can clearly see in my picture that my example and Uncle Jack had it right. The pipe size for the petcock is 1/8 NPT.
(Message edited by paulmikeska on November 15, 2015)
Off to find a 1/8 NPT tap. Yes, I did check for the plastic plug, I can see the threads in the hole.
Are you working on a new Brassworks radiator or a used one ? I've installed several new Brassworks rads and never had to touch the petcock threads !
I had a honey-comb once that had a straight thread petcock tap...drove me nuts until I figured it out but that turned out OK too as I threaded a pipe with straight threads on one end, pipe thread on the other, added a coupling, and the petcock then it sat low enough you could actually see it rather than just go feel for it...
I just installed a new brassworks rad in my 26. It seemed when I put the petcock in that it was tightening with only a short amount of the nipple in. They may be stopping their thread cutting a little shallow. Running a tap in and cutting a little more should fix the problem.
Its a new Brassworks radiator bought from Langs. Apparently they had a major piece of equipment go down resulting in a significant backlog of orders, I waited over 2 mos for mine. Neither the old nor new petcocks would even begin to grab threads. I wonder if in their haste to address the backlog things got short changed.
Finding a 1/8 NPT tap proved difficult. None of my usual sources locally had one (NAPA, Autozone, Home Depot, Lowes), everybody knew what it was but nobody stocked them, so I ended up ordering it from Amazon. That proved easier said then done since the Vermont tap was listed as an "add-on" item. I still don't know what that is, but it wouldn't let me add it to the cart. Ended up finding a different manufacturer that wasn't listed as "Add on". Never thought putting on a new radiator would be such a pain.
Actually not all pipe threads are tapered. NPSM are National Pipe Straight Mechanical. Normally used for adapters and such. NPTF IS National Pipe Taper Fitted and is very close on the thread crown tolerances between the male and female threads. The tops of the threads are truncated in order for the threads to crush and make a dry seal. NPTF threads are normally used in a high pressure application such as high pressure (10,000 psi) application.
PTF work on the same principal as NPTF only are one thread shorter in order to seal where the material is thinner and still needs a dry seal.
NPT is National Pipe Tapered and is designed to be used with dope or Teflon tape. A lot of people all
So people erroneously put tape on NPTF threads and actually weaken the seal. And compromises the the strength necessary to withstand high pressure applications.
I am not aware of any applications where a Model T radiator needs to withstand 10,000 psi. Most of them I worked on were vented and working at about 0 PSI. I could be wrong. All petcocks I have run in to in about 40 + years of working on Model T's have been 1/8 NPT. YMMV
Michael, I was interested in your response. On our galvanised water piping, the male threads are indeed tapered. However, the female threads in the joining sockets are not. The seal is made when the male thread tightens in the socket. That was how I saw the threads in the radiator bottom outlet, the NH carb elbow socket and the fuel tank petcock hole. Each brass item which screws into those orifices has a tapered thread entering into a non-tapered threaded hole. If the carb hole was indeed tapered, it would make aligning the elbow with the fuel line easier, as the hole could be tapped a little deeper to allow the elbow to be turned further.
Allan from down under.
The Model T radiators are made to USA specs, so the hole is threaded tapered.
Go to Harbor Freight, last time I checked their cheapie tap & die set included a 1/8" NPT tap. Set will probably cost you less than one good tap & for one-time use, will be more than adequate.
Tap arrived today, so tried it out on the radiator. Couple twists until it seated, then tried the petcock. Screwed in fine, but bottomed after only a couple turns, same as Dale. Ran the tap in a little deeper to actually cut some new threads and tried again. Petcock screwed in nicely and to what seemed like a correct depth, 10 min. tops.
Mounted the radiator, which took the usual amount of futzing, but will position and clamp the hoses tomorrow, getting dark out.
Light at the end of the tunnel. Was starting to despair I would have this done before it got too cold to work in the trailer. We want it for our usual sojourn to Florida for the Winter Tour.
You have "metric" pipe threads, where indeed the female threads are straight and the male are tapered. The sizes and thread pitches however are not metric, hence the "metric" in quotes.
If you need odd or hard to find taps and dies, try Drills and Cutters.com, I recently purchased the dies to chase the front axle threads, right and left hand, not expensive. I also have the #14X24 taps for the magnets and Bendix cover.