MTFCA Forum

OK, Guys and Gals,
I am having a major brain issue.
The petcock for the radiator needs to be replaced.
After pulling the old petcock out the threads are really messed up.
Is there a helicoil thread repair for this application?
According to Lang's the it is 1/8 pipe thread.
If there is such a helicoil fix for this what size should I get?
Or should I just run a tap thru and hope for the best?

Thank you in advance!

Lots of discussion here: viewtopic.php?f=2&t=45627&p=347143&hili ... ad#p347143

If you run a tap into the hole to clean up the threads, be careful not to go too far. The tapered tap can enlarge the hole such that the petcock threads will now be too small to tighten up before bottoming out.

You can buy the kits;
https://www.threadtoolsupply.com/search ... %22+Length
You can do a search of product out there online. Do a search with " inclosing the item you are looking for. Such as: "1/8" npt Helicoil repair kit"

Is the female thread in the outlet a tapered thread? It is not uncommon for the male thread, the one on the petcock, to be tapered and threaded into a parallel thread. Do you need a tapered tap to clean up the thread in the outlet?

Allan from down under.

Steve, my Tarrant special tourer with the fuel tank hanging under the spare tyre carrier at the rear of the car, has a vacuum tank to draw fuel to the carburetor. If I leave it stand for long, it needs to be primed via small plug hole in the diecast top. Rather than ruin the diecast tank top with repeated fitting of the tapered plug, I have fitted a brass fitting in place of the plug, and the plug then screws into it. Now the plug is removed from the brass fitting if I need to prime it.
You could do the same for your radiator, with perhaps a soldered joint between the fitting and the outlet. Then the petcock will screw into your new brass fitting.

Hope this helps.
Allan from down under.

Never seen a helicoil for pipe threads. There are other options.

It sort of sounds like you’re talking about the petcock threads. Have you tried a better or new petcock? I’ve cleaned up the threads on one of my radiators with a 1/8” pipe tap and it worked OK for me. If yours is still a little loose use some Teflon tape and it should take care of it.

If the radiator is otherwise good and free of leaks and clean and does not cause the car to overheat, then it is worth saving. But remember that if that pet cock comes out, you will lose all your coolant and could severely damage the engine. So If it were mine I would find someone who is an expert welder and braze up that fitting on the radiator then drill and re-tap the threads. Then when you insert the petcock, use a bit of white teflon tape around the threads. After you fill it up with coolant, check for leaks.
Norm

Being somewhat lazy and pragmatic I would probably clean the existing threads immaculately (maybe even retapping a half a thread to expose new metal), wirebrush the male threads, apply enough J B Weld to fill the male thread and reassemble with very light pressure. Wait until tomorrow and then drive until the old radiator finally gives up the ghost. Being a relatively low pressure, no solvent, and low torque application I believe the repair would last a lifetime.

Erik Barrett wrote: ↑

Wed Dec 04, 2024 8:55 pm

Never seen a helicoil for pipe threads. There are other options.

See my post

Cheap option. Get a 1/8" mpt x 1/8" fmpt fitting in brass. clean up the threads as little as you think you can get away with J-B weld that
( if you must) then screw the petcock into that fitting , it will have a hex on it so you can back it up with a wrench.
Craig.