On Sat, 07 Sep 2019 07:49:15 -0700, Joerg
wrote:

On 2019-09-06 18:14, Jeff Liebermann wrote:
On Fri, 06 Sep 2019 16:59:03 -0700, Jeff Liebermann
wrote:

On Fri, 06 Sep 2019 15:30:48 -0700, Joerg
wrote:

What should I use? Piece of plastic? Aluminum? Glue it in place?
Anything needed on the outside except maybe a washer?

Image search for "Presta to Schrader rim adapter":
https://www.google.com/search?q=presta+to+schrader+rim+adapter&tbm=isch
Plenty of styles to choose from.

I saw those but wanted to avoid having to wait for yet another shipment.
The LBS doesn't have any such specialty stuff.

Sigh.

If I feel like it and have time I might make one of these with a Dremel
and a file, then glue it in place so it won't fly off when replacing the
ti
https://www.dutchbikebits.com/image/...76-500x500.JPG

Well, if you're going to make your own, the outside thread on the
Presta stem is M6x0.80. Unfortunately, the standard size tape is
M6x0.75. However, a little brute force will probably make it fit with
the added bonus of not needing any thread lock. To center the stem in
the hole, a small o-ring, aluminum wire bent in a circle, or some
solder for a compression fit, should work.

Or, just make a suitable shoulder washer in a lathe (or drill press).

One of my bicycles uses these:
https://i.stack.imgur.com/m5vqB.jpg
https://www.ebay.com/itm/362302505553
The thread fit was rather loose so I applied some Loctite blue to the
threads. I also wanted to keep water out of the rim, so I installed
small rubber o-rings from the plumbing bins at the local hardware
store.

I am not concerned about the outside as I can simply use a washer and a
homemade rubber gasket. More concerned about the inside being squeezed
into the hole when at the usual 110psi of my road bike.

The washer takes care of centering the stem. If the washer is
sufficiently hard and the same thickness as the rim, it should prevent
the stem base from extruding itself through the hole. Extra credit
for calculating the surface area in sq-in of the washer and multiply
by 110PSI to estimate the force applied to the base. I would do this
for you, but the battery in my digital calipers is dead. Might as
well use a ruler. Schrader hole is 0.32 diameter. Presta stem, about
0.24. Area of washer is:
(Pi * 0.32/2 ^2) - (Pi * 0.24/2 ^2)
= 0.080 - 0.045 = 0.035 sq-in
Pressure is:
0.035 sq-in * 110 lbs/sq-in = 3.9 lbs
That's hardly any pressure and will barely bend the stem base, much
less extrude it through a Schrader size hole.

However, Andy
wrote not to worry so I won't worry. If there is a loud bang and the
valve rockets towards outer space I just tell the other guys that Andy
had blessed it :-)

The only time I really worry about something is when the experts tell
me not to worry. For example, not warning you to deburr or chamfer
the Schrader hole in the rim because the previous owner may have used
a dull drill bit.

There are currently 500,000 pieces of space debris being tracked by
various government agencies. None of these appear to be Presta
bicycle valves, so I suspect launching one into orbit is unlikely.
https://www.nasa.gov/mission_pages/station/news/orbital_debris.html

Valve stem adapters are not rocket science.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558