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blakekrone
05-05-2013, 11:18 PM
So the boat I bought in CA probably never had its drain plugs removed and I had to remove them last fall to dry block the engine before having it hauled back to MN. I went to put back in the plugs today and 1 side went in without any trouble, the other side however doesn't seem like it wants to bite at all. The plugs themselves look a little rough around the edges so I picked up a new 3/4" NPT plug and that won't even bite either. It looks like the manifold was so rusted out that the threads have deteriorated to nothing for the first few turns. Is it worth it trying to rethread with a tap or do I just need to get a new manifold?

JimN
05-05-2013, 11:56 PM
So the boat I bought in CA probably never had its drain plugs removed and I had to remove them last fall to dry block the engine before having it hauled back to MN. I went to put back in the plugs today and 1 side went in without any trouble, the other side however doesn't seem like it wants to bite at all. The plugs themselves look a little rough around the edges so I picked up a new 3/4" NPT plug and that won't even bite either. It looks like the manifold was so rusted out that the threads have deteriorated to nothing for the first few turns. Is it worth it trying to rethread with a tap or do I just need to get a new manifold?

Look for a 3/4" tapered plug or fitting. If that won't grab, go one size up, maybe metric. If it won't grab a new plug, re-tapping won't work because the tap is the same size. You could also install a brass barb fitting on both manifolds (use JB Weld on the stripped one), so you can use the hose & coupler they added to the boats in about '98. It makes draining a lot easier and the fittings in the manifolds don't have to come out.

XtwentyNot
05-06-2013, 12:25 AM
94544
94545

And a tap from a local parts store is how I fixed mine five years ago.

Skipper
05-06-2013, 07:30 AM
You might also be able to clean out the threads on the manifold with a wire cone attachment on your drill.

JimN
05-06-2013, 07:47 AM
You might also be able to clean out the threads on the manifold with a wire cone attachment on your drill.

I used to see this, so I bought a 3/4" tap. If it's rusted too badly, the tap will remove rust and leaves the hole too large because removing rust removes metal, too.

mikeg205
05-06-2013, 09:33 AM
Keep them holes oiled up to keep the threads in good shape... the rust creeps outside in and inside out.. a little maintenance goes a long way..

blakekrone
05-06-2013, 10:12 AM
Keep them holes oiled up to keep the threads in good shape... the rust creeps outside in and inside out.. a little maintenance goes a long way..

Exactly why I'm debating buying a new manifold. I plan to keep the boat for awhile so it might be worth it instead of having to deal with it each year.

blakekrone
05-06-2013, 03:53 PM
Quick update, was a nice day for a drive and I haven't towed the boat yet any distance so I decided to run up to midwest mastercraft. They checked it out real quick with their tap and said that should work so I ran around looking for a 3/4" tap, finally found one and now I'm good to go it appears. Should know tomorrow when I start it up.

Hoping to hit the lake for an hour tomorrow night just cruising.

88 PS190
05-06-2013, 04:08 PM
Good result, due to the taper you can usually salvage it, even if you have to thread deeper.

Table Rocker
05-06-2013, 04:22 PM
Good result, due to the taper you can usually salvage it, even if you have to thread deeper.
Yep, it will probably even look better with the plug not sticking out so far.

Cloaked
05-06-2013, 04:24 PM
Quick update, was a nice day for a drive and I haven't towed the boat yet any distance so I decided to run up to midwest mastercraft. They checked it out real quick with their tap and said that should work so I ran around looking for a 3/4" tap, finally found one and now I'm good to go it appears. Should know tomorrow when I start it up.

Hoping to hit the lake for an hour tomorrow night just cruising.Use Never-Seize when you put the new plug(s) in...

88 PS190
05-06-2013, 04:24 PM
Agreed, I've been planning this same project just to get more threads engaged, mine only thread in about 1.5 threads.

Cloaked
05-06-2013, 04:29 PM
Agreed, I've been planning this same project just to get more threads engaged, mine only thread in about 1.5 threads.
I'll say this (as I have many times before)... a few threads of engagement is OK, just whatever it takes.

I put my plugs in expecting them to leak and while watering the engine, I tighten the plugs only to the point that they no longer leak. Stop, not one more turn..nothing... the plugs will be fine and stay there until wrenched back out....

Been down that road and those threads will easily strip. Just tighten enough to stop the leak...

.

Ski-me
05-12-2013, 10:58 AM
OK, I now also have the same problem. I'm trying to determine if the 3/4 NTP is the same thread size/pitch as the 3/4" galvanized plug at Lowes (or the 3/4" gas black pipe). The threads line up with my old plug. I just want to make sure before trying to get these one.

I couldn't find a brass fitting (tee, reducer) to match the same thread pitch. The ones I found were more coarse.....like a hose type thread. I saw a lot of MIP type threads, but no NTP's.

Does Lowes/HD have a 3/4" tap this size? Is it a common one?

j.mccreight@hotmail.com
05-12-2013, 11:04 AM
OK, I now also have the same problem. I'm trying to determine if the 3/4 NTP is the same thread size/pitch as the 3/4" galvanized plug at Lowes (or the 3/4" gas black pipe). The threads line up with my old plug. I just want to make sure before trying to get these one.

I couldn't find a brass fitting (tee, reducer) to match the same thread pitch. The ones I found were more coarse.....like a hose type thread. I saw a lot of MIP type threads, but no NTP's.

Does Lowes/HD have a 3/4" tap this size? Is it a common one?

NPT (national pipe thread) is what you need, yes any big box store should have the plugs and taps.

Footin
05-12-2013, 11:08 AM
I had the same problen a few years back, I chased the threads with a 3/4 NPT tap then installed 1/4 turn ball valves on each side. Now when I winterize I just turn the valves to drain, no more removing the plugs.

blakekrone
05-12-2013, 11:08 AM
NPT (national pipe thread) is what you need, yes any big box store should have the plugs and taps.

On the contrary none of the big box stores here in my area had NPT plugs nor taps. I ended up getting plugs from the local MC dealer and Northern Tool had a tap set that included the 3/4" I needed.

j.mccreight@hotmail.com
05-12-2013, 11:13 AM
Find a sears hardware, they should have them...

JimN
05-12-2013, 11:37 AM
OK, I now also have the same problem. I'm trying to determine if the 3/4 NTP is the same thread size/pitch as the 3/4" galvanized plug at Lowes (or the 3/4" gas black pipe). The threads line up with my old plug. I just want to make sure before trying to get these one.

I couldn't find a brass fitting (tee, reducer) to match the same thread pitch. The ones I found were more coarse.....like a hose type thread. I saw a lot of MIP type threads, but no NTP's.

Does Lowes/HD have a 3/4" tap this size? Is it a common one?

Look at a piece of threaded black pipe- the thread is tapered, to ensure a good seal when it goes into a fitting.

Go to an ACE hardware store- they have a set of sliding panels with bins, filled with brass fittings.

Ski-me
05-12-2013, 11:59 AM
Look at a piece of threaded black pipe- the thread is tapered, to ensure a good seal when it goes into a fitting.

Go to an ACE hardware store- they have a set of sliding panels with bins, filled with brass fittings.

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.

mikeg205
05-12-2013, 12:07 PM
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.. :)

Table Rocker
05-12-2013, 01:01 PM
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 (http://www.amazon.com/High-Speed-Steel-Straight-Pipe/dp/B00268D0EC), 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/B0046A88OK/ref=oh_details_o04_s01_i04?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.

JimN
05-12-2013, 09:14 PM
The hole isn't tapered, only the plug or other fitting is tapered.

Table Rocker
05-12-2013, 09:20 PM
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.

JimN
05-12-2013, 09:52 PM
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.

Table Rocker
05-12-2013, 10:16 PM
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/hardware/taper-pipe-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.

Ski-me
05-13-2013, 11:42 AM
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.

Table Rocker
05-13-2013, 04:32 PM
That should have you taken care of for years. Job well done.

psychobilly
05-14-2013, 11:49 AM
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!


Sent from my iPad using Tapatalk HD

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

Snipe
05-14-2013, 12:40 PM
I had the same problen a few years back, I chased the threads with a 3/4 NPT tap then installed 1/4 turn ball valves on each side. Now when I winterize I just turn the valves to drain, no more removing the plugs.
Pictures??

Ski-me
05-14-2013, 07:57 PM
OK, got them uploaded finally!

I did find the tap at Ace but it was in a different packaging than the smaller one. We initially missed it but I went back and found it sitting on the bottom shelf rather than with all the others in a pretty display.

http://img.photobucket.com/albums/v69/nielson2020/Mastercraft%20205%201994/DSC_0353_zpsacb9d480.jpg (http://smg.photobucket.com/user/nielson2020/media/Mastercraft%20205%201994/DSC_0353_zpsacb9d480.jpg.html)

http://img.photobucket.com/albums/v69/nielson2020/Mastercraft%20205%201994/DSC_0354_zps1619d567.jpg (http://smg.photobucket.com/user/nielson2020/media/Mastercraft%20205%201994/DSC_0354_zps1619d567.jpg.html)

http://img.photobucket.com/albums/v69/nielson2020/Mastercraft%20205%201994/DSC_0355_zps56a5843d.jpg (http://smg.photobucket.com/user/nielson2020/media/Mastercraft%20205%201994/DSC_0355_zps56a5843d.jpg.html)

http://img.photobucket.com/albums/v69/nielson2020/Mastercraft%20205%201994/DSC_0356_zps23b468a5.jpg (http://smg.photobucket.com/user/nielson2020/media/Mastercraft%20205%201994/DSC_0356_zps23b468a5.jpg.html)

http://img.photobucket.com/albums/v69/nielson2020/Mastercraft%20205%201994/DSC_0358_zpsc114a3e7.jpg (http://smg.photobucket.com/user/nielson2020/media/Mastercraft%20205%201994/DSC_0358_zpsc114a3e7.jpg.html)

http://img.photobucket.com/albums/v69/nielson2020/Mastercraft%20205%201994/DSC_0359_zpsd7f4634f.jpg (http://smg.photobucket.com/user/nielson2020/media/Mastercraft%20205%201994/DSC_0359_zpsd7f4634f.jpg.html)

http://img.photobucket.com/albums/v69/nielson2020/Mastercraft%20205%201994/DSC_0360_zpsde47bada.jpg (http://smg.photobucket.com/user/nielson2020/media/Mastercraft%20205%201994/DSC_0360_zpsde47bada.jpg.html)

XtwentyNot
05-14-2013, 10:37 PM
Nicely done!