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  #21  
Old 05-12-2013, 12:07 PM
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Quote:
Originally Posted by Ski-me View Post
So, if it's tapered, will a 3/4" -14 tap work to clean out the threads?? I'll check out Ace today if I can break away......

The plug I pulled out matches the black pipe but whose to say the old one is correct. I guess I'll have to assume it is after all these years.
Yes correct... putting never(anti) seize on petcock and knock sensor threads recommended as well.

While I'm at it I always spray my blots with my favorite penetrating oil. no rusty or corroded bolts. At 18 years old I am also cleaning up oxidized connection points with contact cleaner - fwiw.. and then coating with some dielectric grease - contact points and connections look brand new... but that's me..
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  #22  
Old 05-12-2013, 01:01 PM
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Quote:
Originally Posted by Ski-me View Post
So, if it's tapered, will a 3/4" -14 tap work to clean out the threads?? I'll check out Ace today if I can break away.....
A 3/4-14 tap will most likely be NPT, but you need to make sure. NPT is tapered on the male and female so the fitting bottoms out and doesn't go straight through like a bolt through a nut.

The only possible confusion would be if you got your hands on a 3/4-14 NPS tap, which would be a fairly rare tool. NPS is straight and does not taper. The steam vent holes in LT-1 heads are NPS.

As for machine thread taps, a 3/4 tap wouldn't even fill the 3/4 NPT hole, so you can't make that mistake. Machine threads are measured on the outside of the threads and NPT is the inside diameter of the pipe. 3/4 NPT will have about a 1" hole.

As for the plugs, I bought two of these: http://www.amazon.com/gp/product/B00...?ie=UTF8&psc=1 The price was way too high, but I like being able to stick a ratchet directly in there to install or remove them and they are brass. A couple of wraps of teflon tape and run them in. I also like the flush face.
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  #23  
Old 05-12-2013, 09:14 PM
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The hole isn't tapered, only the plug or other fitting is tapered.
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  #24  
Old 05-12-2013, 09:20 PM
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Quote:
Originally Posted by JimN View Post
The hole isn't tapered, only the plug or other fitting is tapered.
So you are saying the threads in the manifolds are NPS? If I was using a tapered plug or fitting, I would tap with a tapered tap.
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  #25  
Old 05-12-2013, 09:52 PM
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Originally Posted by Table Rocker View Post
So you are saying the threads in the manifolds are NPS? If I was using a tapered plug or fitting, I would tap with a tapered tap.
The tapered fittings wedge in place, which is the reason they don't pass through. You can use a straight plug, but you would need to seal it and I haven't seen those in brass.

Think about how far a tapered tap would go into the hole. Once it jams, it won't go any farther.
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  #26  
Old 05-12-2013, 10:16 PM
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Quote:
Originally Posted by JimN View Post
The tapered fittings wedge in place, which is the reason they don't pass through. You can use a straight plug, but you would need to seal it and I haven't seen those in brass.

Think about how far a tapered tap would go into the hole. Once it jams, it won't go any farther.
NPT taps are tapered 3/4" per foot and are by far the most common pipe thread type. They do "jam", but you can continue to cut threads as far as you want to go with the tap. It does require some force since you are cutting more material as you go deeper. Back and forth with plenty of oil is the key when cutting threads.

With a tapered tap and die, the male and female threads seal the entire length of the engaged threads. There is a good illustration here:
http://www.engineersedge.com/hardwar...pe-threads.htm
NPT and NPS use a different pilot drill with the tapered threads requiring a smaller hole.

NPS threads are uncommon and are primarily used with thing like banjo fittings like the steam vents on the LT-1. I had to order a NPS tap to clean up the threads on my heads as nobody carried them locally. The seal there is made by compressing rubber lined washers, so it doesn't rely on the threads to seal. I don't know why they would use NPS on a manifold drain when all the plugs would be NPT.
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  #27  
Old 05-13-2013, 11:42 AM
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Well, I did find a 3/4 NPT tap and went ahead and cleaned everything up. It actually worked out quite well! I used a little bit of wheel bearing grease to catch any metal shavings as I was working the threads. I then used a 3/4" brass reducer with teflon and then a 1/2" brass plug. Started it up and no leaks! Looks great and tidy now.

I did take pics (of course) so I'll get those up when I get a chance.

thanks for all the help. I'm now ready to get it on the water.....hopefully Wednesday after work.
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  #28  
Old 05-13-2013, 04:32 PM
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That should have you taken care of for years. Job well done.
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  #29  
Old 05-14-2013, 11:49 AM
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Table rocker hit the ail on the head and you are on the right track using Teflon on the threads. In this application it's best IMO.

We use a thread in the oil patch which is similar if not same. We call it 8 round. I used to use this a lot years ago and when testing these types of connections with test plugs, even with Teflon we would wear out the threads due to it being an interference type connection. I had one that wouldn't hold an 7k test one day and an old hand taught me a trick hat will stay with me forever. The Teflon just wouldn't seal it cause it was sooooooo wore out. The old hand used electrical tape in place of Teflon. Wen we made it up the friction melted the electrical tape and it held like a jug.

NPT in carbon steel is very forgiving. Now when you get into SS, well that's another animal.

Nice work man!


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  #30  
Old 05-14-2013, 12:34 PM
mayo93prostar mayo93prostar is offline
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I also recommend to use teflon tape on the threads because it makes it so much easier to remove the plugs.
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