Well done Macflurry. Blue Peter badge and bar for this thread.
I must learn to do my own valves, as I dread the day that Carl Harrison retires. I always entrust this job with him, the only job I don't do myself.
From my observations and not experience... I think when all the measuring is done and it's time to remove the collets or "half rings". You can slip the belts off and keep the piston at TDC to catch the valve. The cam can then be rotated to the best place to get the rockers out of the way.
A magnetic probe (screwdriver or whatever) should be used to pick the collets out.
This is particularly useful if the rings have broken up, which mine seem to do every time!
Not sure if the allen key would stop the little bits that result?
I thought that MBP collets fit the standard shims, I believe that one of the selling points is that they fit them better than the half rings?
I have heard that the MBP collets can embed themselves into the valve stems making them impossible to remove without having the head off and cutting the valve.
Edit... Oops sorry I almost duplicated DD's post!