Headset problems

I have a set of threaded forks and have a real problem with the headset bolts coming loose, I have had the cups out and the bearings and checked the thread on my stem and all seem fine.

However once I tighten the headset up all I need to do is brake slightly and headset comes loose again, I don't want to over tighten the headset and wreck the cups.

Its not something i've come across before.

It's a common problem with threaded headsets. Try a little Loctite on the locknut.

You do have a locknut, right? Tighten the cup by hand, hold the cup steady with spanner, tighten the locknut down onto the cup without rotating it...

Sorry if I'm teaching you to suck eggs, but it's difficult to tell someone's level of mechanical experience on a forum.

Lae thanks for the help, i have tried both of the above and the bugger just wont stay tight, when i over tighten the steering stiffens up. I have tried different tensions with the locknut but to no avail.

Could possibly be one of the cups not square in the frame, but without having a look it is a bit hard to tell.
To the bike shop I think!

slightly overtighten bottom nut then tighten top nut, then bring the bottom on it's own back up a bit.

Could possibly be one of the cups not square in the frame, but without having a look it is a bit hard to tell.
To the bike shop I think!

Or remove/clean/re-grease/re-install for free, see if that does it. While it's out you can check that the headtube faces are flat/level; it could be that the headtube needs facing.

Do you have one of those washers with a little lump that fits into a channel in the steerer? Helps with this sort of thing. Looks a bit like this:

Yep its got a lock washer on thats why im bemused as to how it keeps popping up when braking.