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
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?
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.
Even if I don't I can probably get a standard one cheap enough.
On 6/9/2013 9:03 PM, email@example.com wrote:
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.
On 6/9/13 8:03 PM, firstname.lastname@example.org wrote:
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.
On Jun 10, 11:31 am, email@example.com wrote:
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
have to screw around with that connection again.
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.
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....
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
some more, it may tighten itself up a bit.
Thanks to all for the suggestions!
On Sun, 9 Jun 2013 17:43:05 -0700 (PDT), " firstname.lastname@example.org"
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.
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.
I was thinking along similar lines, ie using a nipple and a cap, so
if I get this straightened out, I won't have to screw with the cast
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
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,
are three 1/4" brass/bronze plugs going into cast iron.
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.
Better to be stuck up in a tree than tied to one.
Larry W. - Baltimore Maryland - lwasserm(a)sdf. lonestar.org
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
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.
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