On the 4V K bikes, in order the change the valve "bukcets" you need to remove the bung in the center of the timing cover and use a BMW special tool to keep the cam chain tensioner depressed when you remove the cam(s) to swap buckets. The part number for this $50 special tool is 112640 and it looks like this:
Using a bit driver and a piece of rope over the lower fork tree you can keep the cam chain tensioner depressed without the need for that special tool:
