Originally Posted by Akadis
If the new cones have flat spots cut for a cone spanner, then I think you will be OK to leave out the keyed washers because you can hold the cone with a spanner while tightening the lock nut. I have seen cones with no flats; they need the keyed washer so tightening the lock nut does not move the cone.
But... and here is the rub....
Make very sure there is no grease between the cone and lock nut, you want these items to lock together and not budge on the road due to vibration. Before you fit them clean them with a grease cutting fluid. Mosy washers are ribbed on the flat to make then grip, if you leave out this washer you MUST have a clean surface tightening on a clean surface.