By top tube I take it you mean steerer tube. By star nut I take it you mean something that takes the place of a star nut, a compression washer of some sort. Could you supply the brand and model of headset? Type and material of fork and steerer tube?
Personally, if it's steel or aluminum, I'd tap it out from the bottom with a dowel. A new star nut should install no problem, even if the inside of the steerer tube is scarred.
A star nut tool is handy, but not essential. You can use the compression bolt (or a longer one with the same thread) to drive it in. Work it in slow, correcting it if it starts getting crooked, and make sure not to drive it in too far where the bolt threads won't reach. The tool sets it at the right depth and has the leverage to straighten it if crooked, but that's all it does. Our shop charges the minimum $5 for the service.
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Originally Posted by
ahsposo
Ski, bike and wish I was gay.