If your bike has a carbon steerer, they usually use an expander plug (see link below). Sometimes this plug can come loose when you tighten on the top cap and pulls it up the steerer tube. Remove the stem, loosen the expander plug and make sure that is is seated level inside the steerer tube, then tighten this expander plug. Put back the stem and spacers making sure that fork steerer is lower by 2-3 mm from the stem. This gap is needed for the headset to be compressed. Thghten the top cap. Once this is snug, then tighten the stem bolts.


http://www.universalcycles.com/shopp...9&category=100