Originally Posted by d_D
It's a long while since I worked on a threaded headset but isn't the point of the washer to make adjustment easier?
There is a grove running the length of the fork and a key on the washer that fits into the grove. This prevents the washer from rotating when you tighten the lock nut. Without the washer the locknut will tighten directly against the race and rotate it during tightening.
With out the washer it is just harder to get the correct ammount of bearing preload.
Washers do more than just make adjustment easier!! A locknut loosen itself from the adjustable cone of the headset over time, due to fretting. From this
brief wikipedia article on washers:
"High quality capscrews require hardened steel washers to prevent the loss of pre-load after the torque is applied (due to Brinelling)."
And from the
article on Brinelling:
"Brinelling refers to surface fatigue caused by repeated impact or overloading. It is a common cause of roller bearing failures, and loss of preload in bolted joints when a hardened washer is not used. "