A weak area of the XS650 engine is the valve adjuster rockers. The adjuster provides a small area of high pressure to actuate the valve. This combined with limited oiling causes premature wear and pitting of the valve stem and adjuster screw.
One method to mitigate this is to intall Porsche 911 "elephants feet" adjusters. The conseuqence is that the rockers need to be machined down 4mm on the threaded side so that the socket part of the "elephants feet" adjuster fits.
First I disassembled the head.
Then the adjusters were machined off precisely (with an angle grinder), and kept cool by plunging the part in water occassionally.
The result is a quiet running engine, with increased life.