Originally Posted 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:
Thanks for the heads up David. I will check tomorrow. I put the valve cover back on to keep the dirt out but there is easy access.
The videos are great.
To the rest of the world.. please note the beautiful backdrop in these videos. This is the area around Vancouver Island. It is beautiful and there is some great riding to be had.