I'm restoring an older puegeot bike, and I want to replace the handle bars. The stem is however seems to be one long piece. I removed the long bolt on the top, but I'm unable to remove the stem post so that I can use my newer handle bars. How do I remove that stem post??
Unscrew the stem bolt a bit and then give it a tap with a rubber mallet. This will help free the wedge that holds the stem in place. If you are unlucky it has seized in the steerer tube. That can be a bit harder to free up.
If you're unfamiliar with French bikes--and their unique dimensions--I recommend looking at this page before attempting to replace anything (specifically the "Some dimensional differences" chart near the top): http://sheldonbrown.com/velos.html
The stem/handlebar clamp diameter may be 25mm (instead of today's standards of 25.4, 26, or 31.8mm). The quill diameter/headset inner diameter may be 22mm (rather than standard 22.2mm for 1" headsets).
Assuming the Peugeot uses the sizes outlined in the chart above: A standard 1" stem will fit new bars but its quill will be too wide for the French headset. A French stem will fit the French headset, but the clamp will be too small for modern bars.
To use modern handlebars/stem, see "Handlebars/stems" just below the chart.
Sorry if the above was more info then needed (it was full of assumptions). In any case, it's a good idea to remove the stem as barba outlined and grease the quill.
I managed to find an SR stem for my '62 that was a perfect fit (probably as ancient as my Peugeot) and fitted some nice randonneur bars which I adore.
You can sand down a modern 22.2 stem to get a good fit and it really is not that hard.
If the wedge is stuck in the steerer you may have to tap it out after the stem is removed... you will have to remove the brake and tap it out from the bottom of the steerer tube...it's not really that difficult.
You need to know the diameter of the bars you want to use and the diameter of the clamp on the stem. If it is the old 25mm French size clamp on the current stem, I doubt you will find bullhorns to match.
There is the ghetto solution of a flip-and-chop of your current bars. To find the right replacement, you really need a caliper to determine clamp size. You also may find you need to change the stem once you get bullhorns on there.