Try our new info resource - "Aladdin's Cave" (Main menu)Just added a separate link to Ash's Dropbox thread (shortcut)
DON'T whatever you do risk drilling it, you will always end up with some swarf loose in the engine, it's really not worth the risk. Take the rocker cover off and do it from underneath, it's very easy on a 500/550 four, on a standard 750 the engine has to come out! So get a rocker gasket and the tappet you need, couple of hours tops even if you've never done it before
i have a nice 3/4 drive britool torque bar that does the job. Try not to be so heavy handed.
Slacken off all the tappets so they are not compressing the valves. Not sure where you live, but if it's anywere near me i have a nice 3/4 drive britool torque bar that does the job. Try not to be so heavy handed.