marvel drain plug

[Ron Tron]

as i said in my last post I'm rebuilding another 9n and going after the carb it took me for ever to unfreeze the throttle and it finally broke after heating and cooling repeating and lubing etc etc..then I went after the drain plug and that took for ever because it was stripped or cross threaded and shoved in tight so as not to leak.....after finally getting it out the nut is history and there are no thread left in the bottom of the bowl hole.......question

there isn't much room to tap before bottoming out. the way the carb is designed........and taps have like a quarter inch lead before starting to cut.........any ideas out there how to approach this problem?

 

[old]

In the long run probably try to find some one who has that part laying around that will sell it to you. I may even have one

 

[TheOldHokie]

(quoted from post at 17:12:21 12/05/14) as i said in my last post I'm rebuilding another 9n and going after the carb it took me for ever to unfreeze the throttle and it finally broke after heating and cooling repeating and lubing etc etc..then I went after the drain plug and that took for ever because it was stripped or cross threaded and shoved in tight so as not to leak.....after finally getting it out the nut is history and there are no thread left in the bottom of the bowl hole.......question

there isn't much room to tap before bottoming out. the way the carb is designed........and taps have like a quarter inch lead before starting to cut.........any ideas out there how to approach this problem?

If it as badly boogered as you describe there probably isn't enough meat left to tap new threads. If you are going to try I would suggest a tap of the appropriate series (the original threads were probably PTF short or PTF extra short), a good solid adjustable machine vise, and a solid tap guide - e.g. drill press spindle. Turn the spindle by hand while feeding the tap.

Is it really worth the time and effort ???

TOH

 

[ZANE]

The plug is a common 1/8" pipe plug that can be had
at any hardware store. Same for the tap.

Wrap the plug threads with teflon tape and tighten
it lightly.

Tempest in a teapot!

Zane

 

[Poppy545]

I have a recently rebuilt carb you can get for $75.00 if you want it. I can send you pictures if you're interested.

 

[TheOldHokie]

(quoted from post at 17:12:21 12/05/14) as i said in my last post I'm rebuilding another 9n and going after the carb it took me for ever to unfreeze the throttle and it finally broke after heating and cooling repeating and lubing etc etc..then I went after the drain plug and that took for ever because it was stripped or cross threaded and shoved in tight so as not to leak.....after finally getting it out the nut is history and there are no thread left in the bottom of the bowl hole.......question

there isn't much room to tap before bottoming out. the way the carb is designed........and taps have like a quarter inch lead before starting to cut.........any ideas out there how to approach this problem?

Just to followup. I have actually tried to do this on damaged bowls and if you want to get "real" pipe threads it is not easy - perhaps not even possible with normal hand tools. I know I have yet to succeed. On the carbs I have tried to repair the bottom of the hole was rounded and the tip of a conventional pipe tap starts hitting the high side at about .375" deep. A regular pipe tap has a chamfer followed by several incomplete threads which means it bottoms before you even get to the first complete thread on the tap.

If you are starting with a stripped out hole that is oversize to begin with it simply makes the problem worse. As soon as the tap hits the rounded bottom it forces the tap sideways giving you partial threads on one side and little if any on the other side. What I wound up with is some ugly partial threads that will grip a new plug and seal with tape or sealant but they are far from perfect and nowhere close to what was put there by the factory. Even with the proper short hole tap the oversize hole means you have to get roughly .200 deeper than the factory did to cut 3 new complete threads and frankly I don't think that much room exists.

YMMV,

TOH

 

[7080316]

When cutting threads for bolts they have several styles of tap, blind hole, bottoming, etc. I am not sure if they make a bottoming tap for pipe threads, but I am with TOH. Just doesn't seem worth it to screw with it. Either replace the part or get another carb in my honest opinion.

Jeff

 

[TheOldHokie]

(quoted from post at 19:59:39 12/05/14) When cutting threads for bolts they have several styles of tap, blind hole, bottoming, etc. I am not sure if they make a bottoming tap for pipe threads, but I am with TOH. Just doesn't seem worth it to screw with it. Either replace the part or get another carb in my honest opinion.

Jeff

The pipe tap equivalent to a UN type bottoming tap is a PTF short or PTF extra short tap. They have a reduced chamfer and are missing the first 1 or 2 complete threads of a normal pipe tap. They are designed specifically for tapping NPT threads in shallow holes but the hole needs to be sized properly for them to work as designed. Starting with an oversize hole puts them too deep to start with and you are back to square one. Alternatively one could use a cutoff wheel to remove the chamfer and even more threads from a regular pipe tap so that you are strating further up on the taper but you would need something like a drill press spindle to hold it centered and plumb as you fed it into the wallowed out hole. Assuming you accomplished that all you have to worry about is the plug bottoming out before it seals ;-)

TOH

 

[souNdguy]

Braze a female 1/8 pipe coupler over the hole, then add plug and go

 

[lha]

Why not fill the hole with JB weld,Epoxy,or
something of that nature,and drill and tap a 1/4-20
short bolt with a fiber washer? I believe it would
work. Just an idea off the top of my head,and
insomnia.

 

[kylemorley]

I'm with Zane on this. It's awfully rare to find a F NPT thread that can't be made to hold "one more time" given a fresh M fitting and a bit of teflon tape or sealant.

You mention a tap won't work because it won't go deep enough before it hits an obstacle. Taps come in different configurations - taper (Ist operation), intermediate (2nd operation), and plug (3rd) depending on whether they will be used to start a thread in a virgin hole, tap an existing thread deeper in a blind hole or blocked hole, or chase out existing bunged up threads.

If you are trying to rethread a blind or blocked hole as in this case, you can improvise your own by taking a cheap 1st operation/taper tap (which is what most hardware store taps are) threading the old hole as deep as it will go, then grinding off some of the tapered part of the end so it will thread deeper, and repeating this until the threads go deep as you require.

 

[TheOldHokie]

(quoted from post at 11:51:25 12/06/14) I'm with Zane on this. It's awfully rare to find a F NPT thread that can't be made to hold "one more time" given a fresh M fitting and a bit of teflon tape or sealant.

You mention a tap won't work because it won't go deep enough before it hits an obstacle. Taps come in different configurations - taper (Ist operation), intermediate (2nd operation), and plug (3rd) depending on whether they will be used to start a thread in a virgin hole, tap an existing thread deeper in a blind hole or blocked hole, or chase out existing bunged up threads.

If you are trying to rethread a blind or blocked hole as in this case, you can improvise your own by taking a cheap 1st operation/taper tap (which is what most hardware store taps are) threading the old hole as deep as it will go, then grinding off some of the tapered part of the end so it will thread deeper, and repeating this until the threads go deep as you require.

We are talking NPTF taper pipe threads - not straight UN type threads where you have taper, plug, and bottoming style taps. AFAIK there is no such thing as a plug or bottoming NPTF tap. I even tried Google and couldn't find one. The closest NPTF equivalent to a bottoming tap that I know of is a "short projection" pipe tap. It is designated [u:8425d897d3]PTF-SAE short[/u:8425d897d3] and is one thread short on the small end which decreases the depth needed to cut to the proper internal NPTF gage line. There is also a [u:8425d897d3]PTF-SAE special extra short[/u:8425d897d3] form that is two threads short. They are sometimes used on automotive fuel systems where the bottom clearances do not permit the use of a normal pipe tap and they require close control of the hole diameter. Nowadays there are other ways to cut those threads - e.g. CNC thread milling.....

Go get a MS bowl and look at the actual situation. Based on the geometry and my personal experience trying to rethread them I suspect it was originally a PTF-SAE short fitting. Cutting new OVERSIZE NPTF threads in it isn't easy. And if you do succeed the major diameter of the female fitting will be larger than standard and the plug will have to go deeper to seal. That may or may not be a problem - I have never got good enough threads to find out ;-) There are a variety of ways to deal with the boogered drain hole (teflon tape and thread goop being two) but rethreading it for a standard self sealing NPTF pipe plug is certainly a very challenging undertaking....

TOH

 

[phil_n]

Hi all. Basically just been lurking while researching for a potential purchase.

Saw this post and thought "What about a Heli-Coil?"

www<dot>stanleyengineeredfastening<dot>com/brands/heli-coil/screw-thread-inserts/types/pipe-thread

(Can't post actual links.)

phil_n

 

[TheOldHokie]

(quoted from post at 15:38:44 12/06/14) Hi all. Basically just been lurking while researching for a potential purchase.

Saw this post and thought "What about a Heli-Coil?"

www<dot>stanleyengineeredfastening<dot>com/brands/heli-coil/screw-thread-inserts/types/pipe-thread

(Can't post actual links.)

phil_n

The link is: [u:e761476ad5]NPT Helicoils[/u:e761476ad5]

I don't think so. The chart says the minimum hole depth for installing a 1/4-18 NPT insert is .578" and that appears to the the length of the insert. I'm also not clear on what the external thread form on the insert is. For a "normal" helicoil it is the same as the internal thread form. If that is the case here the NPT helicoil requires an oversize NPT hole and you are back to square one. If you can tap the hole oversize for the helicoil you don't need the helicoil - just screw the plug in deeper.....

TOH

 

[Bob]

Or, just braze the hole shut, drill an 11/32" pilot hole, and tap back to 1/8" NPT.

 

[Tall T]

I'd try installing a [b:8b90a22278]drain tap[/b:8b90a22278] with Locweld or Devcon Plastic Steel. Quick and easy and you have a convenient bowl drain to boot.

But that's just me and what do I know . . . according to some, nothing.

 

[souNdguy]

Yup

 

[Tall T]

Funnily enough, I think it was you who suggested I put a drain cock in my own carb . . . and I always give credit where credit is due.

 

[Ron Tron]

(quoted from post at 14:12:21 12/05/14) as i said in my last post I'm rebuilding another 9n and going after the carb it took me for ever to unfreeze the throttle and it finally broke after heating and cooling repeating and lubing etc etc..then I went after the drain plug and that took for ever because it was stripped or cross threaded and shoved in tight so as not to leak.....after finally getting it out the nut is history and there are no thread left in the bottom of the bowl hole.......question

there isn't much room to tap before bottoming out. the way the carb is designed........and taps have like a quarter inch lead before starting to cut.........any ideas out there how to approach this problem?

Hey guys ..........thanks for all the helpful suggestions......I tapped it with a 7/16 by 20 tap and put a allen bolt in it and it doesn't leak........had to cut the allen bolt because the shortest I could find was three quarter inch but ran a nut on it and cut it just past the nut and its working fine except its a little crooked (tap apparently went in at an angle) but its all good......thanks again for all the helpful suggestions.........

 

[souNdguy]

I've seen others do it too. Not an original idea, but has its uses.


On another nite, I see you've met Hobo.

 

[TheOldHokie]

(quoted from post at 17:32:19 12/06/14)

(quoted from post at 14:12:21 12/05/14) as i said in my last post I'm rebuilding another 9n and going after the carb it took me for ever to unfreeze the throttle and it finally broke after heating and cooling repeating and lubing etc etc..then I went after the drain plug and that took for ever because it was stripped or cross threaded and shoved in tight so as not to leak.....after finally getting it out the nut is history and there are no thread left in the bottom of the bowl hole.......question

there isn't much room to tap before bottoming out. the way the carb is designed........and taps have like a quarter inch lead before starting to cut.........any ideas out there how to approach this problem?

Hey guys ..........thanks for all the helpful suggestions......I tapped it with a 7/16 by 20 tap and put a allen bolt in it and it doesn't leak........had to cut the allen bolt because the shortest I could find was three quarter inch but ran a nut on it and cut it just past the nut and its working fine except its a little crooked (tap apparently went in at an angle) but its all good......thanks again for all the helpful suggestions.........

That thread is the same as an SAE -4 (1/4") ORB port. and a $.50 socket head port plug would fit and seal nicely.....

TOH