The answer is that the metal fingers on the clutch plates are slowly wearing grooves into the slots on the outer basket and inner hub. So when you are engaging the clutch, the plates are being pressed together as designed, but catching just slightly so that the engagement is not completely smooth. This manifests as a judder or noise as the plates vibrate against each other just before they're pressed together hard enough to quiet down.
BMW's answer is to use a 5w-40 oil. Specifically, they recommend:
Motor Oil Power 1 Racing 4T 5W-40 4L BMW Part# 83 12 2 153 837
They have also redesigned the clutch assembly on the newer K13 bikes, which parts can be retrofitted into a K12. But sometimes, the K13 bikes still get that judder . . .
If all you're getting is a slight judder/noise, then you probably have a lot of miles left before there's a serious problem. But if you keep the bike long enough, you will be putting a clutch into it.
Originally Posted by kbmwrs
So the consensus is, its an acceptable sound?
It is an expected sound. Whether it is acceptable to you or not is your call.
'13 Dark Graphite Metallic K16GTLD, 24K miles and counting...
'09 Magnesium Beige Metallic K13GT, 60K miles miles and counting...
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All lower 48 states plus Alaska on the K13GT in two weeks . . .
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