I currently have a Shimano 600 headset 1" threaded prolly from about 1986. I put it on my new road bike and i know i did it correctly cuz I had 3 other technicians oversee my work when i was doing it. The problem i am having is it keeps coming loose after every 30km and I have to retighten it. My boss took a look at my fork and he suspects that the fork I got was cut about 1-2mm too short for the bike. The result being the headset cant keep its grip to the fork as the fork is too short for the frame. The previous owner had a 105 headset on the bike and it worked no problems tho. I measured his headset and the height of the upper bearing cup (is that the right term) is about 1-2mm shorter than the one on my 600. Would this be the reason why it always stayed tight. I tried removing the spacers from the upper headset but no luck. Any suggestions. If i cant make this headset work, is there a shorter headset that I can purchase. If not and there is no solution I will just purchase another SL fork. I got about 50 of them in the shop.