I just bought a Mongoose Tirage bike and I'm having trouble assembling the (headtube,stem, stem bolt). I know I'm supposed to align the handlebars and the stem and than tighten the stem bolt, but when I drop the stem bolt into the stem, it doesnt reach the headtube and therefore nothing gets screwed in.

I would really appreciate any insight anyone can provide.
Thanks.

From the pix of the bike it has the slant nut type stem with the bolt screwed into a cylinder of iron that has a slant top that cams against the slant bottom of the stem and jams into place. The stem has to insert far enough into the head tube for this camming action to occur. The pix suggest 1.5-2.5cm between the bottom of the angled part of the stem that goes to the bar and the top of the headset. An alternative type is the wedge, where the bolt threads into a cylinder with a conical section that jams into the bottom of the stem which is split and has a female conical section contour. Tightening the bolt spreads the split ends and jams the stem into place. Both mechanisms require sufficient depth of insertion for the wedge/cam action to occur. The stem should be reasonably tight friction fit into the headtube for these mechanisms to work and minimum depth of insertion will be 5-7cm. Steve