Bicycle Mechanics - Stem instal question

Just got a new stem and the clamp part where it attaches to the fork tube is about 1/4 inch taller than my old one. This has lead to a larger gap between the top of the fork tube and the top of the stem clamp. How big can this gap be and still be safe? The fork tube is about even with the upper bolt on the stem clamp.

What is the steerer material; carbon, steel or Aluminum?

For carbon you want the steerer as fully inside the stem as possible and, preferably sticking out above it so a top spacer is required.

For metal steerers you can be a little more adventurous but I'd want the top bolt of the stem completely below the top of the steerer.

Are there any spacers under the stem you can remove to lower it a bit? If not, a different stem is probably a better idea.

I'm going to go a bit against the grain here, and will probably be roundly flamed, but I want you to think about this. The old stem worked fine fox a certain amount of time. The new stem has no less actual engagement on the steerer, regardless of what sticks out.

The key thing to consider is where the pinch bolt (or the upper of a pair) is relative to the steerer. If it's well below the end of the steerer you're no worse off than you used to be, so don't sweat it.

The key thing to consider is where the pinch bolt (or the upper of a pair) is relative to the steerer. If it's well below the end of the steerer you're no worse off than you used to be, so don't sweat it.
No flames and I agree with your premise, However, the OP said the top of the steerer is about even with the bolt so it sounds like the bolt is not fully supported. Particularly if it's a carbon steerer, I'd be concerned.

I didn't notice the sentence about the steerer height with reference to the upper pinch bolt. It's less than ideal, but probably still workable, and the problem isn't one of safety. The issue is that overtightening the upper bolt can distort the stem and steerer within.

To avoid problems, extra care should be taken when tightening the upper bolt, and if it were me, I'd shift the clamping force balance toward the lower one, tightening that slightly more than I might otherwise (only if needed to hold properly), and go easier on the upper.

BTW- many carbon fork makers say that this arrangement voids their warranty because it increases the likelihood of splitting the end of the steerer, so if it's a carbon steerer it's something to consider.

I would not try that.
Perhaps you can use a stem with one pinch bolt, and place the compression plug centered behind the pinch bolt.

Is removing or changing size of spacer(s) below the stem clamp not an option to adjust for the taller clamp? Seems like taking out about 1/2cm spacer ought to do the trick. Rule of thumb for the gap is about 3mm; it can be bigger as long and top gap bolt can thread effectively into the star nut. But I agree with other posters that not having steerer tube above the clamp bolt is not a good situation. On a related note, every stem I have the clamp part is 40mm; I thought that was kind of the standard but I guess not.

On a related note, every stem I have the clamp part is 40mm; I thought that was kind of the standard but I guess not.
Apparently not. I just measured 6 different threadless stems with two-bolt steerer clamps. Five of these have 40 mm clamp heights. The 6th, an FSA, has a clamp height of only 34 mm.

It's a carbon fork but the upper tube is alum. It's an 06 Schwinn SSGS flat bar road bike. New stem is a bontrager that I belive is alum. It's this one. http://bontrager.com/model/00744. I can remove a spacer but the reason for the new stem was that I needed to get more height so I went from the stock which I think was a 7 deg to a 25 deg with the same length. I'd like to keep it as high as I can and still be safe. I've got about 5-6 full turns of the top bolt into the star nut. When I look through the back of the stem the upper bolt blocks the top of the fork tube so the top of the tube about right in the middle of that top bolt. I just don't want to pull the bars off or bend up the top of the fork tube or some such thing. It's an XL frame and I'm 6'4 205 if that would make any difference.

I'm cautious in this type of situation. I would remove enough spacer material so that you can get that upper pinch bolt below the top of the steer tube.

I'd remove 3 to 5 mm of spacer. The reduction in bar height will be slight but it's worth it to have the bolt completely below the top of the steerer.