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Valve core thread dimensions



 
 
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  #1  
Old September 21st 06, 04:31 PM posted to rec.bicycles.tech
Mike Kennedy
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Posts: 1
Default Valve core thread dimensions

Does anyone know what the thread dimensions are for a value core or the
threaded end of a valve extender? I have a split in the valve stem of a TUFO
tubular-clincher and I thought that I would cut the section off that has the
split, tap the section left and install an valve extender. Anyway I need to
know what threading to tap.

Thank you,

Mike Kennedy


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  #2  
Old September 23rd 06, 05:39 AM posted to rec.bicycles.tech
[email protected]
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Posts: 7,934
Default Valve core thread dimensions

On Thu, 21 Sep 2006 15:31:46 GMT, "Mike Kennedy"
wrote:

Does anyone know what the thread dimensions are for a value core or the
threaded end of a valve extender? I have a split in the valve stem of a TUFO
tubular-clincher and I thought that I would cut the section off that has the
split, tap the section left and install an valve extender. Anyway I need to
know what threading to tap.

Thank you,

Mike Kennedy


Dear Mike,

There are actually two threads on a typical Presta valve stem.

One is the long base, which is wide and threaded for the jam nut that
is tightened down to the rim. "Smooth" Presta valves lack this
threading.

The other threaded section at the end of the valve. It's narrower than
the main body of the valve stem, has only about 3 threads, and is for
the valve cap (or a typical valve extender).

So your scheme may not work too easily, even if you know the thread
pitch and find a die. It sounds as if you want to cut off the end of
the valve stem with the crack, including the short, narrow part that
the valve cap or typical extender just barely threads onto.

If so, you'll have an uncracked stub left, but it will be too thick
for a typical valve extender and will have to be turned down somehow
before threading.

In any case, I'm damned if I can find either thread pitch on the
internet, even in the U.S. Patent Office site. I've emailed a company
that makes extenders and asked if they'll reveal the secret dimension.
A real mechanic would simply measure the threads with a gauge, but
I've seen enough loosely-fitting extenders to wonder just how easy the
measuring of such small threads is. Most of the extenders that I've
seen worked much better with a couple of twists of teflon plumber's
tape around the threads to seal the connection.

You'd also have to cut the very end off a Presta valve to get the
little knurled nut off, slip the valve through the extender, and put
the screw back on.

A new Tufo clincher-tubular is probably a lot less fuss.

Cheers,

Carl Fogel
  #3  
Old September 23rd 06, 11:51 AM posted to rec.bicycles.tech
[email protected]
external usenet poster
 
Posts: 883
Default Valve core thread dimensions

On Fri, 22 Sep 2006 22:39:11 -0600, wrote:

On Thu, 21 Sep 2006 15:31:46 GMT, "Mike Kennedy"
wrote:

Does anyone know what the thread dimensions are for a value core or the
threaded end of a valve extender? I have a split in the valve stem of a TUFO
tubular-clincher and I thought that I would cut the section off that has the
split, tap the section left and install an valve extender. Anyway I need to
know what threading to tap.

Thank you,

Mike Kennedy


Dear Mike,

There are actually two threads on a typical Presta valve stem.

One is the long base, which is wide and threaded for the jam nut that
is tightened down to the rim. "Smooth" Presta valves lack this
threading.

The other threaded section at the end of the valve. It's narrower than
the main body of the valve stem, has only about 3 threads, and is for
the valve cap (or a typical valve extender).

So your scheme may not work too easily, even if you know the thread
pitch and find a die. It sounds as if you want to cut off the end of
the valve stem with the crack, including the short, narrow part that
the valve cap or typical extender just barely threads onto.

If so, you'll have an uncracked stub left, but it will be too thick
for a typical valve extender and will have to be turned down somehow
before threading.

In any case, I'm damned if I can find either thread pitch on the
internet, even in the U.S. Patent Office site.


Shraeder external - 0.305-32 (5/16-32 UNEF will do)
Schraeder internal - 0.206-36 (#12-36 is a bit big)
Presta main - m6-0.75
Presta cap - m5-1.0
  #4  
Old September 23rd 06, 05:49 PM posted to rec.bicycles.tech
Marcus Coles
external usenet poster
 
Posts: 197
Default Valve core thread dimensions

wrote:
On Fri, 22 Sep 2006 22:39:11 -0600,
wrote:

On Thu, 21 Sep 2006 15:31:46 GMT, "Mike Kennedy"
wrote:

Does anyone know what the thread dimensions are for a value core or the
threaded end of a valve extender? I have a split in the valve stem of a TUFO
tubular-clincher and I thought that I would cut the section off that has the
split, tap the section left and install an valve extender. Anyway I need to
know what threading to tap.

Thank you,

Mike Kennedy

Dear Mike,

There are actually two threads on a typical Presta valve stem.

One is the long base, which is wide and threaded for the jam nut that
is tightened down to the rim. "Smooth" Presta valves lack this
threading.

The other threaded section at the end of the valve. It's narrower than
the main body of the valve stem, has only about 3 threads, and is for
the valve cap (or a typical valve extender).

So your scheme may not work too easily, even if you know the thread
pitch and find a die. It sounds as if you want to cut off the end of
the valve stem with the crack, including the short, narrow part that
the valve cap or typical extender just barely threads onto.

If so, you'll have an uncracked stub left, but it will be too thick
for a typical valve extender and will have to be turned down somehow
before threading.

In any case, I'm damned if I can find either thread pitch on the
internet, even in the U.S. Patent Office site.


Shraeder external - 0.305-32 (5/16-32 UNEF will do)
Schraeder internal - 0.206-36 (#12-36 is a bit big)
Presta main - m6-0.75
Presta cap - m5-1.0


The other approach is to thread the stub internally and use a removable
presta valve used on some brands of tubulars and at least some
Continental inner tubes.

I have no clue as to the thread for this.

Marcus
  #5  
Old September 24th 06, 03:18 PM posted to rec.bicycles.tech
Mike Kennedy
external usenet poster
 
Posts: 1
Default Valve core thread dimensions

Outstanding! I will give this a try. At worst I will need to buy a new tire.
Thanks for everyones reply!

Mike

wrote in message
...
On Fri, 22 Sep 2006 22:39:11 -0600, wrote:

On Thu, 21 Sep 2006 15:31:46 GMT, "Mike Kennedy"
wrote:

Does anyone know what the thread dimensions are for a value core or the
threaded end of a valve extender? I have a split in the valve stem of a
TUFO
tubular-clincher and I thought that I would cut the section off that has
the
split, tap the section left and install an valve extender. Anyway I need
to
know what threading to tap.

Thank you,

Mike Kennedy


Dear Mike,

There are actually two threads on a typical Presta valve stem.

One is the long base, which is wide and threaded for the jam nut that
is tightened down to the rim. "Smooth" Presta valves lack this
threading.

The other threaded section at the end of the valve. It's narrower than
the main body of the valve stem, has only about 3 threads, and is for
the valve cap (or a typical valve extender).

So your scheme may not work too easily, even if you know the thread
pitch and find a die. It sounds as if you want to cut off the end of
the valve stem with the crack, including the short, narrow part that
the valve cap or typical extender just barely threads onto.

If so, you'll have an uncracked stub left, but it will be too thick
for a typical valve extender and will have to be turned down somehow
before threading.

In any case, I'm damned if I can find either thread pitch on the
internet, even in the U.S. Patent Office site.


Shraeder external - 0.305-32 (5/16-32 UNEF will do)
Schraeder internal - 0.206-36 (#12-36 is a bit big)
Presta main - m6-0.75
Presta cap - m5-1.0



  #10  
Old September 26th 06, 08:35 AM posted to rec.bicycles.tech
Werehatrack
external usenet poster
 
Posts: 1,416
Default Valve core thread dimensions

On Tue, 26 Sep 2006 00:31:05 +0000 (UTC),
(Luns Tee) wrote:

In article ,
Werehatrack wrote:
On Sat, 23 Sep 2006 10:51:51 GMT,
wrote:

Presta main - m6-0.75
Presta cap - m5-1.0


Both of those are remarkably uncommon sizes. Good luck finding a tap
or die in those thread and diameter combinations outside of a
specialty tool supplier.


I don't believe these threads are correct. The presta valves
I've measured have inch-based thread pitches - 32 and 24 tpi
respectively.
But in this case, I think the OP was looking for neither of
these, but rather the internal thread in a removable-core valve stem.
That, I haven't measured.

However, I think it's a moot point: there's more going on inside
the valve stem than just that thread - the seating area that the valve
core seals against needs to be shaped appropriately too, and it seems
like more trouble than its worth to try to reproduce it all.

Were it me, I'd probably just slather some epoxy in the stem
where the crack is, and permanently glue an extension in place, letting
the epoxy seal whatever crack is there.


I rechecked the dimensions; 6x.75 and 5x1.0 are correct for Presta
externals on all of mine. 1.0 is very close to 24tpi, and .75 is
close to 32tpi, but the thread guage for the metrics was clearly a
better fit than the US guage. While mixed metric/inch thread choices
have been seen elsewhere on bikes (notably on some Raleigh bits as I
recall), the Presta stem apparently isn't one of them.
--
Typoes are a feature, not a bug.
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