Originally Posted by
cyccommute
Yours is a well known issue to any old mountain biker out there. I've replaced dozens of the damned things and loath them for just this reason. The threads just aren't up to rigors of off-road pounding. In the mid 80s to the mid 90s, loosening headset even sparked a cottage industry of locking mechanism to keep it from happening. Theadless solved the problem completely and elegantly.
You can still find some of the headset locks around.
Cambria has some and there are others around. You could also swap to a threadless set but you'd need a 1" fork, a 1" threadless headset, and a 1" threadless stem. Not all of them...the stem in particular...are easy to find nor would the conversion be cheap. I'd start with the thread locking mechanisms.
I have suspected that it was a design deficiency, since the advent of threadless came after the threaded headset issues became so obvious back in the day.
It really boils down to relegating the bike to road use and picking up a more modern mountain bike. A nearly 30 year old mountain bike (with a nicely dented top tube) isn't worth putting much money into.