On Jun 10, 3:22*pm, "Pete C." wrote:
RBM wrote:

On 6/9/2013 8:43 PM, wrote:
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?
can you get a tap and just try chasing the threads?

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.- Hide quoted text -

- Show quoted text -

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....