Bicycle Mechanics - presta valves

First drop bars road bike here, just looked it up...its a Trek 1200 from 1991.

Went to check it out today and could not get the tires to hold air. Bought it anyway ($100).

Got it home and I can get the rear to hold air because it has this brass colored (presta valve?) spring inside. When I touch it it lets air out. I miss schrader valves already......again, why did they invent the presta?

Anyhow, the front has the fitting coming through the rim, but no brass colored flexible looking spring. Can I just drop by the bike shop and pick one up or do I need a special tool to insert it. Maybe it just screws in by hand, but like a schrader it needs a tool to apply force to seat it.

And another one, there was this part that I pulled out, it was essentially a brass colored nut that was on the valve that I cannot get back on (but I see no reason for it) because the presta valve is slightly bent. But Im sure I can get some pliers on it and thread it on if neccessary.

The bike is in pretty good shape but I wont know until I can get that front tire to hold air.

There are no springs on presta valves. Hard to tell from your description (pics would help) but sounds like you may be better off buying new tubes and reading up on how a presta valve works before installing and inflating the. I was leary of them at first but they are easy to deal with once you understand them.

Sounds like you need a new tube. No removable parts to a presta valve

http://www.sheldonbrown.com/brandt/presta-schrader.html

It's fairly common for the valve portion to blow out of presta valves. All you'll see is a hole...They are not repairable.
They are not hard to use; you need a proper pump head of course. Unscrew the little lock ring all the way, give it a little tap to break the seal, and fit the head carefully over the valve.

.....again, why did they invent the presta?

Because they don't leak air back out when you're pumping them up.

I was leary of them at first but they are easy to deal with once you understand them.

I hate, hate, HATE them. They are far more prone to accidental damage while airing them up than Schraders.

I hate, hate, HATE them. They are far more prone to accidental damage while airing them up than Schraders.

How do you damage a stem when pumping up a tire?

My problem lately is finding tubes locally that don't have stems 2" long!

......again, why did they invent the presta?
Because Presta valves are lighter, simpler, and narrower, so the rim can be very light and narrow and not have its strength compromised as much as it would if it were drilled for a Schrader.

How do you damage a stem when pumping up a tire?

I wish I knew. I only have one bike that has Presta and I'm fixing to sell it so I'm not going to worry about it.

I haven't damaged a presta tube by inflating it. I have, however, damaged a tube trying to pull the pump head from the valve. Most presta tubes are threaded all the way. I like the stems with no threads. It is easier to remove the pump head without damaging the tube. They are also more aerodynamic, but I am not sure if I could notice that difference.

I love presta valves...buy decent quality tubes (I get the cheapest ones from Jensonusa.com or Pricepoint.com, they are heavy but durable) and have had ONE valve rip out, entirely my fault for not being more...gentle;) I have been using them for 9 years now, and only like them more each time. Just push in the valve core first before pumping to break the valve seal so you dont break a pump (I love lifetime warranties on pumps!).

I actually hate schrader valves on bikes now. I have one bike that takes them and it will be given to my dad if he wants it.

Sounds like you need a new tube. No removable parts to a presta valve

http://www.sheldonbrown.com/brandt/presta-schrader.html


It's fairly common for the valve portion to blow out of presta valves. All you'll see is a hole...They are not repairable.
Not true. There are presta valves with replaceable cores, and, they do make the cores for sale.
http://www.biketiresdirect.com/ptuvcr/tufo_presta_valve_core/pp.htm
http://www.ebikestop.com/kenda_presta_valve_cores_bag_of_ten-TU6010.php

I would have gotten you a pic, but I was pumping up the tire and finally got it to work. See I took off the locknut and then it began to pump easier and I got the pressure I wanted. After that I released the pump and I guess it shot out of there because the air rushed out and nothing but a hole there now.

So I thought I just needed two valves, but it seems I need two tubes now.

The spring I was referencing to is I guess the valve core (as it would be on a schrader). I bent it back straight and then the locknut would thread by hand. Now its gone, wonder where it ended up!?

How do you damage a stem when pumping up a tire?
Poor technique. People can break the valves by sloppy, rushed, overly forceful pumping. (I've used presta for years and I don't think I've ever broken a valve.)

I have broken a presta stem when using a mini pump. But then again as far as Im concerned mini pumps suck. Two of them broke when I needed them most. I now carry cartridges with an inflator head. Light and reliable.

I would have gotten you a pic, but I was pumping up the tire and finally got it to work. See I took off the locknut and then it began to pump easier and I got the pressure I wanted. After that I released the pump and I guess it shot out of there because the air rushed out and nothing but a hole there now.

So I thought I just needed two valves, but it seems I need two tubes now.

The spring I was referencing to is I guess the valve core (as it would be on a schrader). I bent it back straight and then the locknut would thread by hand. Now its gone, wonder where it ended up!?

You should never remove the nut at the top of the presta valve. You loosen it until you feel the resistance from it hitting the top of the threads and then fill the tire/tube. When you are done you hand tighten it down, which prevents accidental losing of air. The valve is held closed by air pressure in the tube, no spring involved. It's essentially a plug at the end of the threaded portion. If you remove the locknut the rest may fall into the tube. I would guess that's why you got the rush of air when you released the hose. The pump has it's own check valve that prevents the air coming back out until you release the head.

The spring I was referencing to is I guess the valve core (as it would be on a schrader). I bent it back straight and then the locknut would thread by hand. Now its gone, wonder where it ended up!?

Try not to bend the valve core, while sometimes you can straighten them sometimes they break off where the metal's fatigued. Stick with the prestas, they're superior for bikes in a couple of ways. Just need to be more careful when airing up and do things a little differently than with a schrader. What are you using to pump them up with?

I would have gotten you a pic, but I was pumping up the tire and finally got it to work. See I took off the locknut and then it began to pump easier and I got the pressure I wanted. After that I released the pump and I guess it shot out of there because the air rushed out and nothing but a hole there now.

So I thought I just needed two valves, but it seems I need two tubes now.

The spring I was referencing to is I guess the valve core (as it would be on a schrader). I bent it back straight and then the locknut would thread by hand. Now its gone, wonder where it ended up!?

Bernoulli's principle in action:thumb: It's inside the tube. The air rushing into the tube as you removed the pump head forced the stem back not the tube. Don't remove the knurled nut as someone else mentioned. Here's a handy, step-by-step guide I've put together for you Presta newbies and Presta abusers

1. Remove the cap and unscrew the knurled nut. You already know not to remove it

http://i144.photobucket.com/albums/r181/cyccommute/IMGP1368.jpg

2. Burp the valve...just a little...to get it free in the stem

http://i144.photobucket.com/albums/r181/cyccommute/IMGP1369.jpg

3. Use the small opening on your pump head. If you have a frame pump you may have to make some modifications by turning the grommet around

http://i144.photobucket.com/albums/r181/cyccommute/IMGP1370.jpg

4. Put the pump head onto the stem and lift the thumb-lock

http://i144.photobucket.com/albums/r181/cyccommute/IMGP1371.jpg
http://i144.photobucket.com/albums/r181/cyccommute/IMGP1372.jpg
http://i144.photobucket.com/albums/r181/cyccommute/IMGP1373.jpg

5. Pump.

6. Remove the pump head

http://i144.photobucket.com/albums/r181/cyccommute/IMGP1372.jpg
http://i144.photobucket.com/albums/r181/cyccommute/IMGP1371.jpg

There will be a rush of air but that's just the pump line emptying. You aren't losing air from the tire. The valve closes because the air inside the tube keeps the valve closed. Very simple mechanism.

Presta's are where it's at. they hold high pressure 10x better than schrader valves. You'll learn to love them.

I stopped by Walmart early this morning since I was ready to ride and all the shops are closed today. My tires are 23c and the best I could find there was 25-34c so I got two of them and a lever/patch kit all for <$10. All went pretty well. I tucked the tubes the best I could and they've held for 10 miles so far. Just getting the last section of tire back on the rim has my fingers still hurting.

The bike came with a Trek mini/frame pump and even has Trek brand water cages.

Thanks for the tutorial. I finally got most of it figured out ever since it was said that my tubes were crap. I kept expecting something to unscrew in the valve like in a scrader.

Now I have to visit the LBS and get a presta valve air gauge.......or can I use the adapter instead, hmm


thanks guys, Im riding now and feel like a big boy and not some unfortunate soul riding a MTB on the streets. Need to get a computer now to monitor any progress I may make.

Peace


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sorry, cannot resize to get it to fit. And the photobucket link plug [IMG] won't work for me either.

You need to lean that blue bike over a little more. The rear tire is still new on the sides.;)

You need to lean that blue bike over a little more. The rear tire is still new on the sides.;)

Don't worry dvs. I has just started riding then and that was my first set of new tires coupled with too much chain lube. Granted, I dont have the roads here you do in Socal (palomar, mountain passes, canyon roads) I found a nice 4 lane frontage road that allowed me to get a knee down and eliminate the strips. However, it wasn't with the M1s pictured, it was with some Z6s. YZF600R btw

Presta's are where it's at. they hold high pressure 10x better than schrader valves. You'll learn to love them.

This is why they use Presta's on 747 tyres and on high psi compressor tanks...

:rolleyes:

"again, why did they invent the presta?"

It's smaller diameter works on very narrow rims where increased strength is needed and on some very narrow rims a Shraeder stem would interfere with the tyre bead.

This is why they use Presta's on 747 tyres and on high psi compressor tanks...

:rolleyes:

Your compressor tank uses a schrader valve as a normal control? Weird. Doesn't change the fact that presta valves are more useful than schrader on a bicycle tube...even if you fill your tires at the local airport or whether you feel the bernoulli principle helps....old farts accustomed to using a gas station to fill their tires or the same compressor fitting to fill their auto/truck tires seem to feel differently...go figure. After years of using both there's no way I'd ever use a schrader on my bikes again.

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Nice cat!

Poor technique. People can break the valves by sloppy, rushed, overly forceful pumping. (I've used presta for years and I don't think I've ever broken a valve.)

Guilty as charged.


Here's a handy, step-by-step guide I've put together for you Presta newbies and Presta abusers

I come under both categories. I'm not sure exactly what happened, but I wasn't getting a good seal on the pump. I think what I did to compensate was to push it on harder, and in my mind I was thinking Schrader because I remember trying to push the pump head on hard enough to depress the valve pin. (Yeah, I know, STOOPID, but at the time my brain was still thinking in terms of Schrader valves.) I tried it again last night and waddya know? It worked.


Presta's are where it's at. they hold high pressure 10x better than schrader valves. You'll learn to love them.

So far I have not found Presta valve tubes to be any different from Schrader valve tubes in terms of air retention. They both leak to the point where I need to air them up after several days. I think the overriding design consideration is simply the smaller diameter for skinnier rims. I still prefer Schrader.

Another advantage is that for a long time when you pumped up a tire with Shraeder valves you had to screw the hose on and off. That took a lot of time and caused lost pressure during the process. Neither would be good for someone racing.

Don't remove the knurled nut as someone else mentioned.



Been a while since we've had a good knurled nut flame war.

Maybe we could have a combo with smooth vs threaded stems.

It has been a while since we re-hashed the Presta vs Shraeder debate... and where is the love for the Dunlop valves ?

It has been a while since we re-hashed the Presta vs Shraeder debate... and where is the love for the Dunlop valves ?

In Europe.

Been a while since we've had a good knurled nut flame war.

Maybe we could have a combo with smooth vs threaded stems.

Not that knurled nut, dufus:rolleyes: The one on top of the stem (not the cap either:rolleyes:)) mjoekingz28 managed to unscrew the itty bitty nut on the very top of the stem innards.