Helicoil or other ideas for 1/4" pipe threads?

[trader4]

I have a gas pool heater that has a 1/4"-18 NPT brass plug that goes into a cast iron manifold. Over time the threads in the cast iron have deteriorated and now I can't get the plug in. I tried a new plug and one of the other plugs from another location.

I checked to see if there is a helicoil for npt and they have it. I'm not sure how the helicoil works for a pipe fitting so that it doesn't leak, but I guess it must work. Problem is that so far, I can only find the insert in packs of 12 for $25, the tap is $45. Then I think you need an insertion tool?

So, any other ideas? It doesn't have to be the most 100% reliable solution, ie if it drips a bit or fails, it's not the end of the world. Also, I'm not even using the pool heater, but I'm not keen on ripping it out either. The area of the plug just has warm water going through it, not super hot. So, I'm thinking to just epoxy it closed. In the Fall to winterize it I can just knock it out. Any other ideas?

[RBM]

can you get a tap and just try chasing the threads?

[trader4]

Yes, that is a good idea. I had thought of doing that, but I didn't have all my tools available here. And then I guess I got so excited by A - finding out they they do make a helicoil for npt B - finding out how much it costs! that I forgot about just trying a tap.

I'm going to see if I have a 1/4" tap tomorrow.

Thanks Even if I don't I can probably get a standard one cheap enough.

[RBM]

I do repairs on cast iron underground fixture mounting boxes. (Kim J-2) They have a cast iron thick cover with 1/2" NPT threads for the fixture stems. Over time they get all coroded and the stems break off. I put the cover in a vise and beat what's left of the stem out of the threads, then chase the threads with a tap and they're practically good as new. If anything maybe a little sloppy, so use more teflon.

[Dean Hoffman]

Would drilling the hole out to 3/8" be an option? A former drinkin' buddy told me the best way to start a tap. Put the tap in a battery powered drill set to the slow speed. I've tried it several times and it does work well.

[gfretwell]

Since this is really just a plug, why not one of those rubber plugs with a bolt in the middle that spreads when you tighten the bolt. They have them at the auto parts store for stripped oil drain plugs.

[nestork]

I'd clean the theads with a 1/4 inch NPT tap and then screw a 1/4 inch NPT nipple (with plenty of teflon tape on it) and a 1/4 inch NPT ball valve into what you have.

From then on, you can simply connect to the brand new brass treads on the 1/4 inch ball valve. And, if those threads eventually wear out in time, just replace the 1/4 inch ball valve with a new one.

You should not have any problem finding 1/4 inch ball valves. I installed 1/8 inch ball valves on the NPT threads in my upstairs laundry room radiators. I purchased those 1/8 inch ball valves from my local Fairview Fittings distributor. If you look under "Hoses and Fittings" in your local yellow pages phone directory, at least one of the companies listed there will stock and sell you a 1/4 inch ball valve. Every plumbing wholesaler in our city or town will sell you a 1/4 inch ball valve if you pay cash too.

[trader4]

I was thinking along similar lines, ie using a nipple and a cap, so that if I get this straightened out, I won't have to screw with the cast iron part again. You would think by now they would have a pool heater design where you could drain it through one brass valve they could put at the low spot. Failing that, doing something like what you suggest on each drain, so that instead of screwing around with anything that is cast iron, it would be only brass to brass. The way it exists now, there are three 1/4" brass/bronze plugs going into cast iron.

[clare]

And if the threads are too far gone, drill it out and tap to 3/8 npt and install a reducer bushing.

[gfretwell]

I suppose if you don't want to invest in any taps, you could epoxy a

1/4" pipe nipple in there and put a cap on it.

[trader4]

I checked and I don't have a tap. But buying a regular tap isn't a problem. So, that's the plan of record right now, try using a 1/4" tap to restore the threads. If it works, I'll put in a nipple so I won;t have to screw around with that connection again.

[Pete C.]

A helicoil relies on re-drilling and re-tapping to a larger size. Can you simply re-drill and re-tap to 3/8" NPT and use a 3/8" NPT plug? That would require only ordinary drills and taps that are cheap and available singly, and of course a new plug.

[dennisgauge]

The cost of the helicoil certainly has to exceed the cost of a new manifold.

I know you're "not keen" on fixing it right, but this might be a good time to reconsider that solution as a possibility.

[jamesgang]

Chasing with a tap has almost always fixed my problems with corroded female pipe thread. That and a little extra teflon tape. The yellow tape for gas is a lot thicker.

[Larry W]

A few ideas in no particular order:

• If the cast iron manifold is thick enough, you may be able to just run a 1/4 inch NPT tap into it and cut new threads. The plug will just set a littledeeper than originally before getting tight.

• Again, if the CI manifold design allows, drill out the hole and tap for

3/8 inch NPT. You could use a 3/8 to 1/4 pipe bushing instead of a 3/8 plug, so the same problem doesn't develop again later.

• There are some other thread choices you could also make here, with a plug sealed by a gasket or O ring, similar to an engine oil drain plug.

• For that matter, there are rubber oil drain plug replacements available pretty cheaply that might be worth trying. The plugs I'm thinking of do not thread into the hole, but expand into it after being released by the installation tool that they are sold together with. Not sure what kind of pressure they can take, though.

• Clean up the threads as best you can and instead of epoxying in a 1/4 inch plug, epoxy in a 1/4" to 1/8" pipe bushing. That way you'll still be able to remove the plug for maintenance if desired.

[trader4]

That's a good point too. You're right. If you have to drill it for a helicoil, might as well just re-tap it to 3/8". I've never tapped cast iron, but I guess it can be done, as the threads got there somehow to begin with.

So, first plan is to try running a 1/4" tap through it to clean up the threads. I found a tap yesterday, that wasn't easy. HD had some tap, but no NPT. Lowes had no taps at all. Tried Autozone parts store, I figured they probably would not have NPT either. Not only didn't they have any NPT, they hardly had any taps at all!

But the Autozone guy suggested trying a old hardware store just up the street. I didn't even know that store existed. It looked like it was out of the 60's. But the guy was sitting there, waiting for me. Told him what I wanted, he walked behind the counter and in 30 secs I had it for $8.

So, I'll let you know how I make out....

[trader4]

Oh, and forgot to mention. I also got a short brass nipple and a valve, per nestork's suggestion. Assuming I get it back together, I won't have to take it apart again.

[trader4]

Update. I ran the 1/4" tap and then installed a short brass nipple with a lot of Teflon tape, followed by a valve. It sent in easier than it should, didn't want to make it up tight, so I didn't push it. But it's not leaking and with the valve, no need to screw with it again. IF anything, I would expect as the cast iron rusts some more, it may tighten itself up a bit.

Thanks to all for the suggestions!

[imnew2nm]

Helicoil NPT inserts work GREAT and are very easy. Cast iron has so much c arbon in it that it drills and taps like butter. There is nothing simpler to work with. Try MSC, ENCO, Grainger, or any real industrial supplier to get the Helicoli kits, They are expensive for a reason, they work. I am a machinist and tool and die maker in plastics. Do this daily

[Matt]

replying to imnew2nm, Matt wrote: Doubt I'll get a reply since this is an old thread.... I'm using an 1/8 NPT helicoil thread repair kit (from grainger). How can I determine how far to tap the hole (since the it's a pitched thread) to get the correct dept of the insert so it's tight enough to seal? I'm taping an aluminum intake manifold for injector nozzles that need to be set to the correct depth. They can't be too loose and be are limited to how far you can tighten them. I can't find info anywhere to set the proper depth! I don't want to run the STI tap in too far and have the threads be too loose to seal the injector when bottomed out.