Exhaust Port inner threads bad

[rockinhorse 45]

I have a 12hp kohler with bad exhaust port threads. I can start a 1 inch pipe but the threads are bad. Has anybody every rethreaded the threads in the exhaust ? I have done some checking threads are NPS 11- 1/2 Is there a certain type of tap i should use?. There are several different styles and want to get the right one.

thanks for your help Karl

[Indy w h 4]

Karl There just standard pipe thread

[gwest_ca-(File Mod) 10,499]

I think you will find they are a tapered pipe thread. There is a pipe thread that is not tapered so what is classified as standard? Get more opinions.

Garry

[Trouty56 565]

Garry is right... What makes you think they are bad. The pipe only screws in a couple turns before you need a pipe wrench.

[Martin 2,130]

i bought a 1"- 11 1/2 NPT tap to clean up any suspect thread issues in exhaust ports. you probably have some threads down in the port a little that have eroded over time and now it looks like they are damaged. its amazing how just running a tap in there can clean them up good enough to get a better bite for the exhaust pipe......

for the k301 the size is 1" there are 11 1/2 threads per inch and it is tapered (NPT)

[MarkPalmer 80]

I'm a bit confused here. Are the threads bad because a lot of resistance is encountered? If so that is normal as mentioned its a tapered thread. Or are the block threads stripped when attempt is made to thread past the starting point?

-Mark-

[rockinhorse 45]

The threads in exhaust are bad. Threads are half full of carbon deposits ,rust , wear. When i start a new pipe it cuts the edge off of the threads on pipe . Will get some pics to show that will help explain. Martin where did you get your pipe tap?

[Anglo Traction 759]

As already mentioned , you need a 1" NPT (National Pipe Thread Taper). NPS is a Straight (parrallel) Thread pattern.

You definately need to clean out all the Theads that are clogged. I do this by hand, but Martin's Tap use is the best way.

This thread pattern should when cleaned, allow you to screw the pipe in by hand to a depth of about 4 threads (0.4 ")BY HAND. You then tighten it a further 3/4 of a turn with a wrench IF it can. You must also use a Sealant on the threads.

Hope this helps.

[pfrederi 17,147]

Pipe taps that big are not cheap...McMaster has them $31 for carbon steel ove $100 for HS. First I would go to the hardware store and by a pipe brush (steel bristle brushes in the plumbing section...they come in sizes. Make sure the exhaust valve is closed and use your shop vac to suck out teh trash you loosen up.

[Martin 2,130]

The threads in exhaust are bad. Threads are half full of carbon deposits ,rust , wear. When i start a new pipe it cuts the edge off of the threads on pipe . Will get some pics to show that will help explain. Martin where did you get your pipe tap?

As already mentioned , you need a 1" NPT (National Pipe Thread Taper). NPS is a Straight (parrallel) Thread pattern.

You definately need to clean out all the Theads that are clogged. I do this by hand, but Martin's Tap use is the best way.

This thread pattern should when cleaned, allow you to screw the pipe in by hand to a depth of about 4 threads (0.4 ")BY HAND. You then tighten it a further 3/4 of a turn with a wrench IF it can. You must also use a Sealant on the threads.

Hope this helps.

Pipe taps that big are not cheap...McMaster has them $31 for carbon steel ove $100 for HS. First I would go to the hardware store and by a pipe brush (steel bristle brushes in the plumbing section...they come in sizes. Make sure the exhaust valve is closed and use your shop vac to suck out teh trash you loosen up.

if you dont need it right away, ebay have them from time to time. mine is hs and i picked it up for $15. one other method i used for quite a while was to get a stainless steel 1" pipe nipple about 3" long and cut relief grooves with a grinder with a cut off wheel around the circumference like a tap. not perfect, but great for getting out carbon and 'straightening' the threads that have been damaged over time.......

[Martin 2,130]

search ebay right now, just came up with a bunch of them, some used ones on there reasonably priced......

search......

1" 11 1/2 pipe tap npt

[Kelly 1,028]

I've used the method Martin said above by cutting groves in a piece of pipe.

[oldredrider 2,547]

Go ahead and open up your wallet...the tap is not THAT expensive as Martin said. It should last a life time and

it's there whenever you need it.

And that's all I've got to say about that.

[rockinhorse 45]

OK Guys i got some pics. The p/o had a flange with about 1/2" inside exhaust port . It was 4" pipe 2 pipe fittings another4" pipe and then a tractor muffler (full size tractor muffler) then rain cap all this was held up by a angle iron bracket bolted to frame. No flange bolts no gasket nothing. Flange was beating on threads plus all the carbon deposits in threads. Hope the pics show how bad the threads are. You guys are right i will get a pipe tap, Does'nt hurt to extra tools around. thanks again for all your help!!! Karl

[rmaynard 14,898]

Just my 2 cents worth, but your threads don't look all that bad from here. I would just chase them with a piece of 1" threaded pipe and some PB Blaster, turning it in a little, out, in a little more, out, etc., until the threads are clean. Remember, because the threads are tapered, you won't get the pipe to turn all the way in.

Then put a little anti-seize on your new pipe, screw it in, and call it a day. :icecream:

[Martin 2,130]

believe it or not those threads arent really that bad. im pretty happy if they look that good to begin with.

yours are very savable, a tap or the method i described with a pipe nipple grooved should clean that up nicely.

sometimes the pipe male thread on nipples arent cut into the end deep enough and it makes it real hard to get a few threads in the port before it goes tight. if you have access to a 1" pipe die that you can cut the thread on the end of the pipe a little deeper that will help also. because the thread is a taper if you reduce the male end and increase the female (exhaust port in this case) it will help you to get more pipe in the hole......

[infernus 8]

Looks good to me, but it still probably wouldn't hurt to chase them out... I agree with the pipe with reliefs cut in it. You might want to hit the pipe with a torch till it glows bright red and throw it in a bucket of water right away to harden it up a bit.