Originally Posted by RoninMoto
I was checking the valve clearance today and they were all loose. I noticed the roller on the exhaust lifter looks warn funny. I sent pictures to my friend Martin at Torque Racing in the UK and he said it looks like the hardening is coming off the roller.
Tomorrow I will adjust the valve clearance back within spec. The rocker will need to be replaced but that will wait until Georgia. I have 1700 km to Tbilisi then I will be giving this bike the TLC she deserves. The snow is calling and I would rather wait for parts on the slopes sipping irish coffee with ski bunnies than waiting for them here in Turkey.
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: