seedsbelize 

Hi All,
I bought a '91 Giant Yukon frameset from a bike co-op in Ohio, brought it down here, and assembled it. Not having a 36 mm headset wrench, I had it professionally adjusted, and I watched him do it. 40 km later, it's so loose I'm afraid to ride it home, but have no choice(I was only 15 km out). I fiddled with it myself, this morning, and could only get the slop out if the steering was also way tight. So I set it tight, put loctite on the threads, tightened down the locknut, and then backed it off incrementally. I know this isn't a proper fix, but don't know what is. New fork? New headset? both?
It loosens with the application of the front brakes.
Thanks,
Seeds

cny-bikeman

If yu had it adjusted why not take it back - should not have come out of adjustment that easily. There may be a missing lockwasher between upper race and loknut, as even without the headset wrench you should be able to gently hold the upper race with a protected pair of channelocks and tighten enough to hold. Really hard to tel what it needs remotely.

JohnDThompson 

Threaded or threadless headset?

If it's a threaded headsetand keeps loosening, examine the threads (both on the steer tube and threaded headset parts) for damage.

seedsbelize 

This guy is independent, and makes his money from the full carbon race types. He does my stuff more as a favor, and charges me practically nothing (75 cents to shim and press in the headset races, for example, on my road bike). Mostly I go to him for advice, as I learn to do my own work. So it's channel locks for me. I thought maybe there was an obvious issue. Guess not. Would the wrong size retainers cause this issue?

Edit: Threaded