Track Cycling: Velodrome Racing and Training Area - Cinelli 1A stem constantly coming loose, argggh!!

Hello,
This is my first post on Bike Forums.
I was hoping that somebody could give me some help with the stem on my bike, that is constantly coming loose. I bought the bike (31 year old track bike made by Rapparee, Irish family business that made high quality bikes) a week ago and since then the handle bars have physicaly come out of the steerer tube during use (starting from a stop) twice.
No matter how much I tighten the expander wedge it still works it's self loose after a few miles. I don't want to carry a 6mm allen key with me everywhere I go.
Please help as I can't trust this bike when i'm using it, which spoils the enjoyment of the lovely bike completely.
Thanks,
Jason.

Are you using the correct diameter bar? That seems like it may be the problem...if they are maybe a groove has been worked into the bars that is making them too small for the stem.

If you are inserting the stem into the steerer tube too far, getting it into the lower section of the steerer tube where it is butted, that can cause the stem to come loose in the steerer no matter how much you tighten it. Here's some info from Sheldon's site on the subject:

"Note: Steerers are butted at the bottom, so the hole in the steerer is constant-diameter until near the bottom, then the walls taper inward in the butted section.
It is vitally important that the stem extender (or stem) not be inserted so far that the wedge is installed where the steerer is narrowing, or it could come loose unpredictably.

When this happens, only the edge/corner of the quill or wedge contacts the steerer, and it is trying to "grab" a slanted surface.

This is sometimes a problem on smaller frames if you try to insert the stem or a stem riser too far down into the steerer."

If you are inserting the stem into the steerer tube too far, getting it into the lower section of the steerer tube where it is butted, that can cause the stem to come loose in the steerer no matter how much you tighten it.

BINGO! We have a winner!

Here's a crude drawing that may help.

http://i32.photobucket.com/albums/d7/k4drd/Bicycles/Tubing/QuillSteminSteerer.jpg

Whoops looks like I misread the question

Thank you for the advice but still no joy :( . I even went to the extreme of letting the stem slide down under it's own weight and then tightening it but still it works it's self loose. The steerer tube on this bike is quite short (120mm) and when the stem is above the fork butting the locking nut is about 20mm below the minimum insertion point, if you know what I mean.

Does anybody have any sugesstions becasue I really don't know what to do!
Jason.

Where are you?

Perhaps you should replace the stem. Nitto uses an angled wedge which may be more secure than Cinelli's expander wedge.