Originally Posted by TheMuffinMan
So rocker arm bearing play. What exactly is to be tested? I want to know personally but since this is one of the main known issues with the bike it'd be great to put a blurb up on the wiki about it as well.
Here is a picture from RoninMoto's (Noah) bike:
You can really see the abnormal wear on the roller.
Some comments made on the roller by Gunnerbuck:
It is not common for the valve clearance to loosen and this usually points to other issues... Normal operation and valve wear will drop the valves farther into their seats and thus reducing the clearances to the tappets...
Usually on the 640 and 690 when the clearances open it means that actual cam follower roller needles are on their way out and have developed slop... When it is run closer to the point of failing the cam follower bearing may quit turning altogether and gall up the camshaft lobe... With a keen ear you can usually notice a change to the tappet noise and how it emits a louder klikety klak before it does any damage... The next time you have the rollers exposed try giving them a wiggle to see if there is slop...
A couple of videos: