1"npt to 1.250" npt?

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blownzoom440
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1"npt to 1.250" npt?

Post by blownzoom440 » Sat May 28, 2011 7:23 pm

i have screw in plugs in the engine block[aluminum plug/iron block]i need to tap the block to 1.250 size because the hole is not tapped completely around and it leaks even with RTV sealer.my Q is will i have to drill to the new tap size or will the tap alone take it there?thanks for the help.
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Re: 1"npt to 1.250" npt?

Post by crazyman » Sun May 29, 2011 2:46 am

Follow the tap's instructions.. Most taps have the drill size listed. If you are careful about roundness and size, you could probably open it up some with a dremel or die grinder.....

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Re: 1"npt to 1.250" npt?

Post by blownzoom440 » Sun May 29, 2011 6:59 am

thanks! here is what i have.
http://www.yellowbullet.com/forum/showt ... p?t=367566
i wonder if i could epoxy it then tap it,is there an epoxy that would work?
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Re: 1"npt to 1.250" npt?

Post by bill jones » Sun May 29, 2011 2:20 pm

-Personally I would NOT attempt to install a larger plug.

-If there is room back up inside the water jacket to run the same size pipe tap in there without bottoming the tap out on some cast iron somewhere---I would probably run the tap in and clean up the threads---maybe another half a turn---and clean the outside surface of the threaded boss flange back about a quarter inch.

-just use a thin smear of JB Weld epoxy on both the block threads and on the plug threads---screw the plug in and then smear the residual epoxy onto the outside edge of the plug and the boss pad to seal it up on the outside.

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Re: 1"npt to 1.250" npt?

Post by PackardV8 » Sun May 29, 2011 2:53 pm

NO, don't even think about going to 1.250".

NPT threads are tapered. On a shallow blind hole, such as a block where the tap cannot be run in deeper, the answer sometimes is to grind quite a bit of stock off the bottom of the tap to thus allow the larger threads further up to cut the full diameter.

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Re: 1"npt to 1.250" npt?

Post by blownzoom440 » Sun May 29, 2011 3:31 pm

i forgot about the threads getting wider and if i could do that.i am certainly going to try it with the same size tap.i have 1.250 to the cylinder wall inside.the larger plug was a last resort if needed.pachardv8 and ordinary builder from YB.com said i could get a plug that was longer and have more to work with and maybe have to cut the tap to tap the block as needed.
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Re: 1"npt to 1.250" npt?

Post by ALKYAL » Sun May 29, 2011 4:06 pm

you have a pm over on YB. Al
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Re: 1"npt to 1.250" npt?

Post by governor » Mon May 30, 2011 10:04 am

Are you sure that it is pipe thread? In the photo it looks more like an O-ring bose thread that would seal with an O-ring under the head of the plug. I would ck it out more before grinding or trying to change the threads any.

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Re: 1"npt to 1.250" npt?

Post by blownzoom440 » Mon May 30, 2011 3:19 pm

i barrowed a 1" tap and it matches the plug threads putting them togather and it screws in the block.i am measuring the tap depth with the block cylinder wall contact.the tap is 1.700 with 18+ threads[taper at the end]i may have to take some off the end but i get good contact with 8 threads left to go.i think i may have to go 3/4 more threads to have the block have threads of some kind.then JB weld an iron plug i guess.
update:sure enough it hits the cylinder wall when the tap starts to make good contact.now how much to cut off the tap.maybe .500[5 threads]
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Re: 1"npt to 1.250" npt?

Post by bill jones » Mon May 30, 2011 4:41 pm

-sometimes you just have to buy the tool and cut it up to make it fit whatever you are doing.

-If you have a pipe plug that looks like it could be screwed into the block say 4 threads further than what your leaky plugs does--but your tap is bottoming out somewhere inside the water jacket and not allowing you to cut the threads another turn or two---then you need to dedicate that tap to that project and shorten it whatever it takes.

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Re: 1"npt to 1.250" npt?

Post by blownzoom440 » Mon May 30, 2011 5:09 pm

i got the go ahead to cut the tap and will do that.i will look fo some iron plugs at the big plumbing supply store near me.[lakewood supply,cleveland,Ohio]i will seal it with JB weld after cleaning the parts good before.
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Re: 1"npt to 1.250" npt?

Post by blownzoom440 » Fri Jun 03, 2011 6:08 pm

i was able to locate some 1"npt plugs but none taller/wider.i went to M.E.Martin co[13811 west parkway cleveland,o.]i got some replacement plugs made of iron and some of brass with the hex drive.i have to go to lakeside supply yet and i called roush racing who did the block work.i left e message at Roush.1.290 is the plug up to 1.299 2 threads later at the end of the plug.i am just passing along info.i will get some JB weld tomorrow along with some acytone[sp] to clean the parts to put togather.
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Re: 1"npt to 1.250" npt?

Post by blownzoom440 » Sun Jun 05, 2011 3:04 pm

i got it in.it did countersink a couple threads and i sealed it with jb weld on the threads and around the plug after install.i tapped it 4 threads and got some contact all the way around.
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Re: 1"npt to 1.250" npt?

Post by DavidPerez » Sat Jun 11, 2011 12:10 am

this one is very helpful

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Re: 1"npt to 1.250" npt?

Post by blownzoom440 » Sat Jun 11, 2011 12:44 pm

i hope it helps someone.i have not been able to find a bigger plug for future info but am looking into threading round stock it the die is big enough to match the tapped block.
"69"satellite,3900lbs,8-71,edel victor heads,I/C,446cu.in W/gas 1250 carbs

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