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cleaning threads on exhaust port.

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Pipe taps are tapered so I don’t think there is a bottoming tap for pipe like there is for straight threads. The measurement for pipe taps is the inside diameter of the pipe. 1” I.D. pipe tap is probably close to 1 1/4” O.D.. The Harbor Freight 1” pipe tap with 11 1/2 tpi is probably what you need. Bottoming taps are usually for straight threads such as bolts in castings with blind holes.
Take a bolt that the same thread and grind in 2 sprial flutes in it and it may work.
 

spndncash

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I
remember it's national NOT british latter has a extra thread
I believe NPT and BSPT are the same thread pitch. the angle of the thread is 60 vs 55 degrees and the thread peaks and valleys are flat vs round. as far as I know US and Canada are the only ones on NPT the rest of the world is BSP/BSPT.
 

Todd

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Me? I'd go to a couple-few pawn shops. Seems every one that I go to has pipe-threading tools in them at a rate.

Of course, generally speaking, yours is not an issue of too much metal that needs removing but, rather, already missing/displaced metal so the entire issue of chasing threads may be academic.
 

mgwin

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Pawn shop sounds like a good possibility. Right much equipment there, pawned by people that have no idea how to use what they have pawned!
Probably no metal removal involved. I would about bet, the main issue would be carbon buildup removal. ;)
 

Greg Riutzel

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For my money I would give this try. 1st thing before I use it on a head I would check it out with a known good female pipe fitting such as an ell or a coupling. If it passes muster, then I would go for the head's threads. One thing I have on my engine's exhaust ell is a locknut to position it tightly to the head to prevent looseness and damage from vibrations. It appears to be nothing more than one of those electrical locknuts as for box connections. It's held on since 1975.

Link: Chaser Tap

Edit: found the same item on Amazon as well
 

jkoenig

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Jim Koenig Halfway between Harvester, MO and Cadet, MO
Greg: One thing I have on my engine's exhaust ell is a locknut to position it tightly to the head to prevent looseness and damage from vibrations.



Be sure to buy the Kohler locknut. Some others on the market are for aluminum blocks that do not hold as much heat as the cast iron K-series. My Kohler guy sold me one that melted. It was my first trip there. I thought it was funny, he refunded my $1.25, we bonded, and he ordered the right one, and we have had a good relationship ever since. He gave me a killer deal on a new crankshaft back when you could still buy a new Kohler crankshaft.
 

charles germer

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I

I believe NPT and BSPT are the same thread pitch. the angle of the thread is 60 vs 55 degrees and the thread peaks and valleys are flat vs round. as far as I know US and Canada are the only ones on NPT the rest of the world is BSP/BSPT.
funny than since the taps i have the BSP shows both the angle and extra thread
 

spndncash

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funny than since the taps i have the BSP shows both the angle and extra thread
first, I am wrong, I broke out the machinery's handbook!
BSPT is 11 threads per inch (1" and larger diameter thread) and NPT is 11.5 threads per inch (on a 1" to 2" diameter threads) I use mostly 1/2-3/4 NPT and BSPT - they have the same pitch 14 (still different thread angles 55 and 60) this was my mistake. BSP is not the same as BSPT. BSP is a parallel thread form similar to NPSM and NPSL. they seal with crush washers, o-rings or other face seals. NPT is a tapered thread as is BSPT they are designed to seal by the thread form, usually with the help of thread sealant, pipe dope, teflon etc.
The thread angle is the angle formed between the peaks of the thread profile.
with all of this said the effective length of thread engagement for a NPT 1"-2" thread is from .68" to .75". our customers have been screwing 1/2" up to 2" NPT into BSPT for over 50 years we have never had any one complaint of blowout or leaks. Air is typically 150-200 psi and water is rarely over 50 psi.
 

rogerdleonard

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i went to harbor freight and bought the set that has a 1” 11.5 tap so i will give that a try. my challenge is going to be getting it started straight. the first threads are the worst.
 

mgwin

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The tap should have a slight taper on the tip to help get it started straight. A dremmel with a wire brush wheel, or similar item should help to clean up the first few threads. This should help to get the tap started straight also. Just remember to back up with the tap about each 1/4 turn forward.
 
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