Ah, do you have the owner's manual?
Originally Posted by KTM Owner's Manual (2003 640a)
Checking and adjusting steering head bearing *
Check steering head bearing for play periodicaly. To check this put
motorcycle on a stand so that the front wheel is off the ground. Now try to
move the fork forward and backward. To adjust, loosen the five clamp screws
1 of the top triple clamp and turn steering stem bolt clockwise 2 until
there is no more play. Donít tighten the steering stem bolt all the way,
otherwise the bearings will be damaged. With a plastic hammer, lightly rap
on the triple clamp to avoid tension. Re-tighten the five clamp screws with
15 Nm (11 ft.lb).
IF THE STEERING HEAD BEARING IS NOT ADJUSTED TO BE FREE OF PLAY, THE MOTORCYCLE WILL SHOW AN UNSTEADY DRIVING PERFORMANCE AND CAN GET OUT OF CONTROL.
! CAUTION !
IF YOU DRIVE WITH PLAY IN THE STEERING HEAD BEARING FOR LONGER PERIODS, FIRST THE BEARINGS AND THEN THE BEARING SEATS IN THE FRAME WILL BE DESTROYED.
At least once a year, the steering head bearings should be greased
(Motorex Long Therm 2000).