Singlespeed & Fixed Gear - Headset clank

My headset keeps clanking when I ride over bumps and what not. I've tightened it but it seems like It won't go away. I ride a Mercier Kilo TT and the headset is stock. My headset was loose for about 2 months but I still rode it loose. Is it because I rode it loose for so long, that I damaged it and need a new one?

Is there a 2-5mm gap between the fork and the top of the stem?

You might have damaged your head tube but more likely it's just still not tightened down properly. Did you check out a tutorial to make sure you're tightening it correctly?

It's also possible your steerer tube is too long and you can't tighten your headset correctly without another spacer or shortening the tube.

Im pretty sure I don't need an extra spacer. Also, I checked the tutorials, I loosened my stem bolts and then tightened the top cap. Doesn't seem to be working. If I overtighten it, It almost goes away.

Is there a 2-5mm gap between the fork and the top of the stem?

+1.

when you've 'overtightened' it and it almost goes away, cinch down the stem (which is what really holds the adjustment, not the top cap) and then completely remove the top cap.

where is the top of the steerer tube in relation to the top edge of the stem. pretty close i'm betting. does the top cap have a step down that drops into the top of the stem 1mm or so? i predict you discover that the steerer is bottoming out on the underside of the top cap, which prevents the preload adjustment from acting on the bearings (ie: you're preloading the steerer).

if so, take 1/8" off the steerer, or add another spacer (on top of the stem is OK if you don't want to change stem position).