I recently got an older road bike and picked up an old pair of 3t bars for it to fit me better. As tight as I can get the 3t stem (without breaking my wrench - VERY tight), the bars still slide downwards with a bit of pressure.

The bars seem to fit the stem fine. They don't have a sleeve, and are do not have grooves around the clamping area, they're smooth and round. Is there any sort of compatibility issue between the bars and the stem that I can check for? Might I need to use bars that are grooved for my stem?

Thanks